Abstract:
The invention relates to methods and apparatus for determining a characteristic of an optical element. The apparatus includes a spatial light pattern generator adapted to generate a beam of light at a predetermined spatial position, at least one lenslet disposed in an array of lenslets adapted to receive the beam of light from the spatial light pattern generator, and to direct the beam of light to the optical element. The apparatus further includes a detector positioned to receive the beam of light subsequent to the beam of light encountering the optical element. The detector is adapted to detect a received spatial position at which the detector receives the beam of light. The apparatus also includes a processor adapted to compare the predetermined spatial position with the received spatial position to determine the characteristic of the optical element. The invention further relates to methods and apparatus for generating a diffraction limited image. The apparatus includes a spatial light pattern generator adapted to generate a plurality of beams of light at selected spatial positions to compensate for a characteristic of an optical element and an array of lenslets adapted to receive the plurality of beams of light from the spatial light pattern generator and to direct the plurality of beams of light to the optical element. The apparatus also includes an image plane positioned to receive the plurality of beams of light subsequent to the plurality of beams of light encountering the optical element and adapted to form the diffraction limited image.

Description:
GOVERNMENT SUPPORT 
     This invention was made with government support under Contract Number EYO4395, awarded by the National Eye Institute. The Government may have certain rights in the invention. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to the field of instrumentation for optical measurements and more specifically to methods and devices for measuring and correcting for optical aberrations in an optical system. 
     BACKGROUND OF THE INVENTION 
     A typical optical system operates on an incident optical wavefront to transform it to a different optical wavefront. Generally, different points on the wavefront experience different transformations depending on what portions of the optical system they encounter. For example, when a wavefront is incident on a lens, those portions of the wavefront that traverse the periphery of the lens will experience phase delays which differ from those experienced by portions of the wavefront which traverse the center of the lens. A wavefront can be defined as a plurality of points having a constant phase. The wavefront encountering the lens results in a transmitted wavefront having a different shape. Appropriately shaping and positioning lenses can modify a transmitted wavefront to a desired shape. 
     In some cases, an optical system is known to produce an undesired transformation. One way to correct the transformation is to add a second optical system designed to correct for the deficiencies of the original optical system. For example, in the case of a human eye requiring a corrective lens, the optical components of the human eye perform an optical transformation which is imperfect. In another example, a flawed objective lens installed in a large telescope performs an imperfect transformation. Rather than replacing the objective lens, it may by preferable to install a corrective lens. In both of these cases, it is necessary to know characteristics of the flawed optical transformation in order to correct it. 
     One method for measuring the optical characteristics of a human eye is the technique of placing lenses having various correction factors in front of the eye and asking the patient whether or not the overall image has improved. Using this substitution technique, one can determine an overall correction for the optical characteristics of the eye. An instrument that is generally used to approximate an optical system that corrects for the flawed optical transformation of an eye is referred to as a “refractometer.” In the case of a general lens system, corrections are determined by a variety of tests, each referred to by its owns name, such as the “Foucault test.” Throughout the following description, the term “refractometer” will be used to refer to all of the instruments that perform such tests. 
     A mathematical model of the eye can be expressed in terms of a polynomial equation. One such mathematical model is known as the Siedel model. The substitution technique described above determines the overall correction for the eye, but it is limited to prismatic, cylindrical, and spherical corrections. These corrections provide only the lowest-order terms of the Siedel or polynomial model of the eye&#39;s optical system. The technique does not correct for the errors that are specified by higher-order terms of the polynomial model. Additionally, it is not possible to obtain point-by-point measurements of the wavefront at designated sites on the optical system using the technique. For example, where the optical system is a cornea, this technique cannot determine the optimal wavefront portion at each point on the cornea. 
     A number of refractometers have been developed that are designed to determine the optimal wavefront at designated sites on the optical system. For example, one such optical system includes a reference optical subsystem for projecting a reference pattern on the patient&#39;s retina through a reference area on the cornea and a separate measurement optical subsystem for projecting a measurement pattern on the patient&#39;s retina through a measurement area on the cornea. 
     To determine the shape of the optimal wavefront at a designated site on the cornea using this refractometer, the measurement pattern is moved across the retina until its location coincides with the location of the reference pattern. Based on the difference between the initial and final positions of the measurement pattern, this refractometer can infer the correction of the wavefront required at the selected corneal site. 
     An example of another refractometer consists of two optical subsystems aligned along substantially the same optical axis: a reference optical subsystem and a measurement optical subsystem. The reference optical subsystem projects a reference pattern onto a reference pattern position on a detector plane through a selected reference site on the measurement plane. The measurement optical subsystem projects a measurement pattern onto a measurement pattern position on the detector plane through a selected measurement site on the measurement plane. The two subsystems may have some or all of their elements in common. 
     In operation, the location of the measurement pattern on the detector can be controlled by an observer through the use of an optical aligner coupled to the measurement optical subsystem. Using the optical aligner, the observer can move the measurement pattern on the detector until it is aligned with the reference pattern on the detector. The distance and the direction in which the observer moves the measurement pattern in order to align it with the reference pattern provide a measure of the shape of the optimal wavefront associated with the portion of the wavefront incident on the selected measurement site on the measurement plane. This method is sometimes referred to the “nulling” method. 
     In an alternate operation, a measurement of the displacement of the measurement pattern from the reference pattern is used to characterize the wavefront. This method is sometimes referred to the “non-nulling” method. 
     Although the devices disclosed above can be used to measure the deviation from the shape of an optimal wavefront at a selected measurement site on the optical system, they are complex and they do not provide an observation of the optical system after correction. 
     SUMMARY OF THE INVENTION 
     The invention relates to an apparatus for determining a characteristic of an optical element. In one embodiment, the apparatus includes a spatial light pattern generator adapted to generate at least one beam of light at a predetermined spatial position. The apparatus further includes at least one lenslet disposed in an array of lenslets adapted to receive the at least one beam of light from the spatial light pattern generator, and to direct the at least one beam of light to the optical element. The apparatus further includes a detector positioned to receive the beam of light subsequent to the beam of light encountering the optical element, and adapted to detect a received spatial position at which the detector receives the beam of light. The apparatus further includes a processor adapted to compare the predetermined spatial position with the received spatial position to determine the characteristic of the optical element. In another embodiment, the processor is further adapted to change the predetermined spatial position in response to the received spatial position. 
     In another embodiment, the spatial light pattern generator includes an opaque mask having a movable aperture. In a further embodiment, the spatial light pattern generator includes a spatial light modulator. In yet another embodiment, the spatial light pattern generator includes an array of individually addressable light-modulating elements. In one embodiment, the array of lenslets is arranged in a substantially uniform pattern. In another embodiment, the uniform pattern is chosen from the group comprising substantially a square, a circle, a rectangle, an ellipse, and concentric circles. In yet another embodiment, the detector is chosen from a group of position detectors, including a retina, an array detector, a quadrant detector, a photodetector, a photodiode, a charge coupled device (CCD) detector, and a photosensitive film. In one embodiment, the optical element comprises an eye, a lens, a mirror, a spherical mirror, a segmented mirror, and a flexible mirror. In one embodiment, the processor includes a computer or control electronics. In another embodiment, the apparatus further includes a contact lens fabrication device coupled to the processor. In another embodiment, the apparatus further includes an intraocular lens fabrication device coupled to the processor. In yet another embodiment, the apparatus fiuther includes laser surgical equipment coupled to the processor. In other embodiments, the characteristic includes wavefront aberration, defocus, astigmatism, and curvature. 
     The invention also relates to a method for determining a characteristic of an optical element. The method includes passing at least one beam of light originating from a predetermined spatial position through a lenslet in an array of lenslets to the optical element. Subsequent to said at least one beam of light encountering said optical element, the method further includes detecting the at least one beam of light at a received spatial position, and comparing the predetermined spatial position with the received spatial position to determine the characteristic of the optical element. The method further includes the step of processing the received spatial position to determine the characteristic of the optical element. The method also includes providing a detector. The detector is chosen from the group comprising a retina, a photodetector, a quadrant detector, a charge coupled device, and a photosensitive film. In another embodiment, the step of passing at least one beam of light includes providing a spatial light pattern generator. In yet another embodiment, the step of comparing the predetermined spatial position with the received spatial position includes providing a processor. In another embodiment, the method further includes the step of changing the predetermined spatial position in response to the received spatial position. 
     The invention also relates to an apparatus for generating a diffraction limited image. In one embodiment, the apparatus includes a spatial light pattern generator adapted to generate a plurality of beams of light at selected spatial positions to compensate for a characteristic of an optical element. The apparatus further includes an array of lenslets adapted to receive the plurality of beams of light from the spatial light pattern generator and to direct the plurality of beams of light to the optical element. The apparatus also includes an image plane positioned to receive the plurality of beams of light subsequent to the plurality of beams of light encountering the optical element and adapted to form the diffraction limited image. In one embodiment, each of the plurality of beams of light is coherent with respect to the others of the plurality of beams of light. 
     In another embodiment, the spatial light pattern generator includes an opaque mask having a movable aperture. In a further embodiment, the spatial light pattern generator includes a spatial light modulator. In yet another embodiment, the spatial light pattern generator includes an array of individually addressable light-modulating elements. In one embodiment, the array of lenslets is arranged in a substantially uniform pattern. In another embodiment, the uniform pattern is chosen from the group comprising substantially a square, a circle, a rectangle, a triangle, an ellipse, a pentagon, a hexagon, an octagon and concentric circles. In yet another embodiment, the detector is chosen from the group including a retina, an array detector, a quadrant detector, a photodetector, a photodiode, a charge coupled device (CCD) detector, and a photosensitive film. In one embodiment, the optical element comprises an eye, a lens, a mirror, a spherical mirror, a segmented mirror, and a flexible mirror. In one embodiment, the processor includes a computer or control electronics. In another embodiment, the apparatus further includes a contact lens fabrication device coupled to the processor. In another embodiment, the apparatus further includes an intraocular lens fabrication device coupled to the processor. In yet another embodiment, the apparatus further includes laser surgical equipment coupled to the processor. In other embodiments, the characteristic includes wavefront aberration, defocus, astigmatism, and curvature. 
     The invention also relates to a method for generating a diffraction limited image. The method includes passing a plurality of beams of light through a lenslet array to an optical element, the plurality of beams of light originating from selected spatial positions to compensate for a characteristic of the optical element. Subsequent to said plurality of beams of light encountering the optical element, the method further includes imaging the plurality of beams of light to form a diffraction limited image. In one embodiment, each of the plurality of beams of light is coherent with respect to the others of the plurality of beams of light. 
     In another embodiment, the step of imaging includes providing a detector. The detector is chosen from the group comprising a retina, a photodetector, a quadrant detector, a charge coupled device, and a photosensitive film. In another embodiment, the step of passing a plurality of beams of light comprises providing a spatial light pattern generator. In yet another embodiment, the step of imaging comprises providing a processor. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other objects, features and advantages of the invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which: 
     FIG. 1A is a schematic diagram showing an illustrative ray trace for an ideal optical system; 
     FIG. 1B is a schematic diagram showing an illustrative ray trace for an imperfect optical system; 
     FIG. 1C is a schematic diagram showing an illustrative compensated ray trace for the imperfect optical system of FIG. 1B; 
     FIG. 2A is a conceptual diagram of a spatial light pattern generator according to an illustrative embodiment of the invention; 
     FIG. 2B is a conceptual diagram of a spatial light pattern generator according to another illustrative embodiment of the invention; 
     FIG. 2C is a conceptual diagram of a spatial light pattern generator according to a further embodiment of the invention; 
     FIG. 2D is a conceptual diagram of a spatial light pattern generator according to an additional illustrative embodiment of the invention; 
     FIG. 2E is a conceptual diagram of a spatial light pattern generator according to another illustrative embodiment of the invention; 
     FIG. 2F is a conceptual diagram of a spatial light pattern generator according to a further illustrative embodiment of the invention; 
     FIG. 3A depicts an array of lenslets in optical communication with a spatial light pattern generator according to one embodiment of the invention; 
     FIG. 3B depicts an array of lenslets in optical communication with a spatial light pattern generator according to another embodiment of the invention; 
     FIG. 4 is a schematic block diagram of an illustrative wavefront sensor for measuring characteristics of an eye according to one embodiment of the invention; 
     FIG. 5 is a schematic block diagram of an illustrative wavefront sensor for measuring characteristics of an eye according to another embodiment of the invention; 
     FIG. 6 is a schematic block diagram of an illustrative wavefront sensor for measuring characteristics of a lens according to one embodiment of the invention; 
     FIG. 7 is a schematic block diagram of an illustrative adaptive optics system for projecting a diffraction limited image according to an embodiment of the invention; and 
     FIG. 8 is a schematic block diagram of an illustrative retinal scan system for obtaining a high-resolution image of the retina according to an embodiment of the invention. 
    
    
     DETAILED DESCRIPTION 
     Typical optical imaging systems are designed to focus distant objects on an image plane. For example, a camera images objects through its lens system onto a light sensitive film in the image plane of the lens system. If the imaging system was ideal, then all of the rays of light entering the system from a distant object such as a star, would be imaged onto the same position on the image plane. In that case, only diffraction from the aperture of the imaging system would limit the sharpness or accuracy of the image. FIG. 1A is a conceptual diagram of such an ideal imaging system  100 . A distant object  102  (i.e., a star) is very far away from the imaging system  100 . Since there is a large distance between the object  102  and the lens  106 , the rays  104  arrive at the lens  106  substantially parallel to each other. If the lens  106  is an ideal lens, it focuses the rays  104  down to the point  112  on the image plane  110 . In a non-ideal system, optical aberrations exist that limit the ability of the imaging system in such systems. In these non-ideal systems, rays of light entering the imaging system at different points are imaged onto different locations of the image plane. 
     FIG. 1B is a conceptual diagram of an aberrated imaging system  100 ′. As in the case of FIG. 1A, the distant object  102  is very far away from the imaging system  100 ′. The rays  104  arrive at the lens  106 ′ substantially parallel to each other. Due to the imperfect lens  106 ′, the transmitted rays  108 ′ impinge on the image plane  110  at different locations  112 ′ creating a blurred image on the image plane  110 . Blurring of the image can also result from the improper placement of the lens  106 ′ with respect to the image plane  1   10 . 
     FIG. 1C is a conceptual diagram showing a compensated ray trace for the imperfect optical system of FIG.  1 B. As in FIGS. 1A and 1B, the distant object  102  is very far away from the imaging system  100 ″. The rays  104  arrive at the correction lens  114  substantially parallel to each other. The correction lens  114  is configured to compensate for the imperfect lens  106 ′. The transmitted rays  108 ″ impinge on the image plane  110  at the point  112  on the image plane  110 . Although the following description is in terms of the ray description of light, skilled artisans will also appreciate that aspects of the invention can be understood using a wave analysis. Although the previous figures are described in terms of lenses, skilled artisans will appreciate that other optical elements such as mirrors can be used. 
     FIG. 2A is a conceptual diagram of a spatial light pattern generator  200   a  according to an illustrative embodiment of the invention. A spatial light pattern generator, as used in the specification, refers to any device that changes a property of light, such as brightness, according to a spatially variable pattern and includes, for example, holes in an opaque masking material, electronically addressable transmissive or reflective arrays, and light sources having controllable brightness patterns. In one embodiment, a spatial light pattern generator is referred to as a spatial light modulator (SLM). In the embodiment shown in FIG. 2A, the spatial light pattern generator  200   a  has a moveable site-selecting aperture  204 . The movable aperture  204  is movable within an opaque screen  202 . The movable aperture  204  is implemented by coupling a stepper motor  206  to an aperture controller  208  and the opaque screen  202 . In response to a signal to the aperture controller  208 , the stepper motor  206  translates the opaque screen  202  including the aperture  204  in the site-selection plane  210 . 
     FIG. 2B illustrates another embodiment of a spatial light pattern generator  200   b . In this embodiment, a spatial light modulator  201  having a plurality of light-modulating elements  212  is shown. In one embodiment, the spatial-light modulating elements are coherent with respect to each other. Each light-modulating element  212  can be switched between an “ON” state and an “OFF” state. One or more light-modulating elements  212  form the aperture  204 ′ whose size, shape and location on the opaque mask  202 ′ can be controlled by the distribution of lightz modulating elements  212  forming the mask  202 ′. In one embodiment, controller  208 ′ controls the light-modulating elements  212 . In another embodiment, the light-modulating elements  212  are liquid crystals. In that case, the ON and OFF states correspond to the transmissive and opaque states of the liquid crystal for a particular polarization of light, respectively. In an alternative embodiment, the light-modulating elements  212  are movable micro-mirrors, in which the ON state corresponds to the position in which the micro-mirror reflects light at a suitable angle to the plane of the mask  202 ′ and the OFF state corresponds to the position in which the micro-mirror deflects light away from the plane of the mask  202 ′ corresponding to the ON state. Skilled artisans will appreciate that other types of spatial light modulators can be used without departing from the spirit and scope of the invention. 
     By utilizing a mask  202 ′ having individually addressable light-modulating elements  212 , apertures  204 ′ of different sizes and shapes are formed. Such a mask  202 ′ is not subject to mechanical stresses such as vibration as is the mask  202  of FIG.  2 A. 
     FIG. 2C illustrates another embodiment of a spatial light modulator  200   c  according to the invention. This embodiment includes one or more light-modulating elements  212 . The lightmodulating elements  212  form aperture  204 ″ whose size, shape and location on the opaque mask  202 ″ can be controlled by the distribution of light-modulating elements  212  forming the mask  202 ″. In one embodiment, controller  208 ″ controls the light-modulating elements  212  through the use of a pointing device  214 . The pointing device  214 , in one embodiment, is a computer mouse as shown in FIG.  2 C. Alternatively, ajoystick, trackball, light pen, or other similar device is used to control the light-modulating elements  212 . In an alternative embodiment, a processor  216  is adapted to control the controller  208 ″. In another embodiment, the processor  216  controls the controller  208 ″ through the use of a feedback loop which couples to a detector (not shown). In an alternative embodiment, the processor  216  records the various positions of the light-modulating elements  212 . Alternatively, the processor  216  tracks the movements of the pointing device  214  by the user. 
     FIG. 2D illustrates a spatial light generator  200   d  of the form of a cathode ray tube  226 . In this embodiment, the deflection of an electron beam  224  is under the control of the controller  209 . The controller  209  couples to the elements  220  and  218 . By manipulating the voltage in the elements  220  and  218 , the controller  209  controls the electron beam  224 . In an alternative embodiment, a pointing device  214  couples to the controller  209  for manipulating the electron beam  224 . 
     FIG. 2E illustrates a spatial light pattern generator  200   e  including an array  228  of individually addressable light emitting elements  230 , such as light emitting diodes (LEDs). In this embodiment, the controller  209 ′ controls which light emitting elements  230  in the array  228  are turned on. In an alternative embodiment, the pointing device  214  couples to the controller  209 ′ and manipulates the state of the light emitting elements  230  in the array  228 . 
     FIG. 2F illustrates a spatial light pattern generator  200   f  including an illumination pattern source  232 . The illumination pattern source  232  includes a uniform light source  234  and an array  228 ′ of individually addressable light-modulating elements  230 ′. In this embodiment, the controller  209 ″ controls which light-modulating elements  230 ′ will block light generated by the uniform light source  232 . In another embodiment, the pointing device  214  couples to controller  209 ″ and manipulates the light-modulating elements  230 ′. 
     FIG. 3A illustrates a lenslet array  300  according to one embodiment of the invention. The lenslet array  300 , in some instances, is referred to as a microoptics array. The lenslet array  300  is comprised of a plurality of lenslets  302  or lenslet elements, sometimes referred to as microlenses, and arranged in a substantially uniform pattern. In another embodiment, the pattern is not uniform. In one embodiment, the pattern is substantially square in shape. In another embodiment, the pattern is substantially rectangular. In still another embodiment, the pattern is substantially circular. In yet another embodiment, the pattern is substantially elliptical. In another embodiment, the pattern includes concentric lenslets. In other embodiments, a pentagonal, a hexagonal or an octagonal pattern is used. Skilled artisans will appreciate that any mathematically defined pattern could be used. Illustratively, each of the lenslets  302  is evenly separated from an adjacent lenslet  302 . In operation, a spatial light pattern  310  generated by a spatial pattern generator  200  impinges on each lenslet  302 . The spatial light pattern generator  200  is located at substantially a focal length F from the lenslets  302 . In another embodiment, the distance between the spatial light pattern generator  200  and the lenslets  302  is less than the focal length F of the lenslets  302 . In another embodiment, the distance between the spatial light pattern generator  200  and the lenslets  302  is greater than the focal length F of the lenslets  302 . In one illustrative embodiment, the light-modulating elements  212  corresponding to the location of the optical axis  304  of each lenslet  302  in the lenslet array  300  are switched ON. This arrangement generates collimated light  306  from each lenslet  302  in the lenslet array  300 . The collimated light  306  exhibits a perfectly planar wavefront  308  propagating away from the lenslet array  300 . As the positions of light-modulating elements  212  are changed within the spatial light pattern generator  200 , the wavefront  308  begins to distort. This distortion is shown in FIG.  3 B. 
     FIG. 3B illustrates the lenslet array  300  in optical communication with the spatial light pattern generator  200 . In this embodiment, the positions of light-modulating elements  212 ′ no longer correspond to the optic axis of each lenslet  302  in the lenslet array  300 . In operation, a spatial light pattern  310 ′ generated by a spatial pattern generator  200  impinges on each lenslet  302 . The spatial light pattern generator  200  is substantially located at a focal length F from the lenslets  302 . This arrangement generates substantially collimated light  306  from each lenslet  302  in the lenslet array  300 . However, the collimated light  306  exiting from each lenslet  302  is tilted with respect to the optic axis of the lenslet  302 . The wavefront  308 ′ is no longer planar due to the deviated rays from the collimated beams  306 . Skilled artisans will appreciate that the wavefront  308 ′ is perpendicular to the rays  312  emanating from the lenslets  302 . 
     In one embodiment, a corrective lens  106 ′ (not shown) located to the right of the non-planar wavefront  308 ′, effectively modifies the wavefront  308 ′ to generate a substantially planar wavefront  308 . In another typical embodiment, the corrective lens  106 ′ is not ideal, causing the modified wavefront  308  to be non-planar. One embodiment of the invention as shown in FIG. 4 selectively modifies a wavefront to generate a desired wavefront. 
     FIG. 4 illustrates a highly schematic block diagram of a wavefront sensor  400  for measuring characteristics of an eye  420  according to one embodiment of the invention. The wavefront sensor  400  is also referred to as a refractometer. The front surface  403  of the spatial light pattern generator  402  contains the light modulating elements  404  and  406 . In one embodiment, the surface  403  is disposed in a plane perpendicular to axis Z of the refractometer  400 . The lenslet array  408  comprises a plurality of evenly spaced lenslets  410  arranged in a planar configuration. In one embodiment, the lenslets  410  are arranged in a square array configuration. In another embodiment, the lenslets  410  are arranged in a radial configuration. In another embodiment, the lenslets  410  are arranged in a hexagon al configuration. In other embodiments, the lenslets  410  are arranged in any geometric or random pattern. In yet another embodiment, the positions of the lenslets  410  with respect to each other is varied. In an illustrative embodiment, the lenslet array  408  is disposed in the plane perpendicular to axis Z of the refractometer  400 . The light modulating elements  404  and  406  are located at a position corresponding to the focal length F of the lenslets  408 . In the illustrative embodiment, the refractometer  400  includes the relay lenses  428  and  430 . The relay lenses  428  and  430  are used to modify the working distance between the user&#39;s eye  420  and the refractometer  400 . Skilled artisans will appreciate that other relay systems including mirrors (not shown) may be utilized without deviating from the spirit of the invention. The relay lenses  428  and  430  are positioned in the plane perpendicular to the axis Z of the refractometer  400 . In the illustrative embodiment, the optical axes of the relay lenses  428  and  430  correspond to the axis Z. In another embodiment, the relay lenses  428  and  430  are located a suitable distance away from the lenslet array  408 . In another embodiment, the distance L between the relay lenses  428  and  430  is fixed. In yet another embodiment, the relay lenses  428  and  430  are the substantially the same. In the illustrative embodiment, the distance L between the relay lenses  428  and  430  affects a characteristic of the optical signal being relayed. 
     The eye  420  will be described next. The perfect eye  420  receives light which is ideally focused onto the retina  412  through the cumulative convergence of the cornea  418 , the lens  419 , and the fluids  421  of the eye  420 . Refractive errors in the eye  420  affect the point of focus of the light. For example, in nearsighted subjects, the point of focus falls short of the retina  412  allowing images close to the eye  420  to be relatively clearly viewed, while blurring distant images. Conversely, in farsighted subjects, the point of focus falls past the retina  412  allowing distant images to be relatively clearly viewed, while blurring images close to the eye  420 . The eye  420  is located with respect to the refractometer  400  such that light exiting the relay lens  430  will impinge on the cornea  418  and be directed towards the retina  412 . In one embodiment, the optic axis of the lens  419  corresponds to the Z-axis. In another embodiment, the optic axis of the lens  419  corresponds to the optic axes of the rely lenses  428  and  430 . In a typical embodiment, the lens  419  is tilted with respect to the Z-axis. This lens  419  tilt can contribute to the aberrations of the eye  420 . In another embodiment, the lens  419  is tilted with respect to the cornea  418 . 
     One embodiment of the operation of refractometer  400  will be described next. In this embodiment, the spatial light pattern generator  402  is a spatial light modulator (SLM). The SLM  402  is an array of light sources, as previously discussed with reference to FIG. 2. A controller (not shown) switches on a single light source  404  from the SLM  402 . Rays  405  from light source  404  impinge on lenslet  410 . The distance between light source  404  and lenslet  410  is predetermined such that the beam  414  exiting lenslet  410  is substantially collimated. The collimated beam  414  is achieved when the rays of light from the beam are parallel to each other. Hence, the collimated beam  414  neither converges nor diverges until it encounters an element that modifies it. The collimation occurs at a distance F, the focal length of lenslet  410 . In another embodiment, suitable collimation occurs at a distance in the vicinity of the focal length F of lenslet  410 . 
     In one embodiment of the invention, the rays  405  from the light source  404  impinge on undesired lenslets  410 ′ and  410 ″ as well as a desired lenslet  410 . A series of baffles (not shown) can be used to control the light from the light source  404 . The baffles are placed between the lenslets  410 ,  410 ′ and  410 ″, to keep stray light from impinging on an improper lenslets  410 ′ and  410 ″. The baffles are not necessary in the illustrative embodiment. 
     Collimated beam  414  next encounters the relay lenses  428  and  430 . In this embodiment, relay lenses are used to vary the working distance between the refractometer  400  and the user&#39;s eye  420 . In the preferred embodiment, the relay lenses  428  and  430  receive the collimated light beam  414  and transmit an inverted but otherwise substantially the same collimated light beam  414 ′. In another embodiment, the relay lenses  428  and  430  have different focal lengths. In that embodiment, the collimated beam  414  has a different diameter than the collimated beam  414 ′. In another embodiment, pluralities of relay lens sets are used. In a further embodiment, suitable is optical mirrors (not shown) are used to relay the collimated beam  414  to a desired location. In yet another embodiment, a combination of relay lenses and mirrors is used. In still another embodiment, a relay mechanism is not required. 
     The collimated beam  414 ′ next encounters the eye  420 . The eye  420  includes a cornea  418 , a lens  419  and fluid  421  which all contribute to focusing the collimated beam  414 ′ onto the retina  412 . In this embodiment, the collimated beam  414 ′ is focused by the eye  420  to the point A  404 ′ on the retina  412 . The point A  404 ′ on the retina  412  represents the light that has entered the eye  420  through a portion of the pupil  426  defined by the image of the lenslet  410 . Next, the single light source  406  is switched on by a controller (not shown). The rays  407  impinge on the lenslet  410  from a different source location than the ray  405 . The light source  406  is at a distance corresponding to the focal length F of the lenslet  410 . The lenslet  410  generates collimated beam  416  corresponding to the light source  406 . The collimated beam  416  encounters the relay lenses  428  and  430 . The relay lenses  428  and  430  invert and relay the collimated beam  416  to generate the collimated beam  416 ′. The collimated beam  416 ′ enters the pupil  426  at the same location as does the collimated beam  414 ′. The eye  420  focuses the collimated beam  416 ′ to the point A′  406 ′ on the retina  412 . As different point sources from different locations on the spatial light pattern generator  402  are illuminated by a controller (not shown), the angle at which the light enters the eye  420  changes. This changes the position of the point A on the retina  412 . In one embodiment, the spatial light pattern generator  402  is a spatial light modulator (SLM). 
     The aberrations in the system can be characterized by exploiting this technique. In one embodiment, each light source in the SLM  402  is sequentially switched on by a controller (not shown), and a corresponding location of that light source image is formed on the retina  412 . Changing the position of the light source changes the angle at which the light enters the eye  420 . The controller (not shown) sequentially switches on various light sources from the SLM  402  until one light source aligns with a reference location on the retina  412 . The position of the reference light source corresponds to the angle in which the light was required to bend through the cornea to contact the reference location on the retina  412 . By mapping the location of the light source versus the position of the image on the retina  412 , the characteristics of the wavefront aberration of the eye  420  are observed, in one embodiment, by a processor (not shown). The controller (not shown) accomplishes this by making successive measurements across each lenslet  410  in the lenslet array  408 . The measurements generate a set of light entry angles for the eye  420 . An estimate of the wavefront aberration for the eye  420  is readily computed from the set of light entry angles. 
     In the embodiment described above, the eye  420  of the user should be fixed on a referenced target, such as a bullseye or a reticle. This is to ensure that the light enters though a fixed portion of the pupil  426  of the eye  420 . In an alternate embodiment, the light impinging on the retina  412  is imaged through another optical apparatus onto a spatially resolved measurement device, such as a camera or an array detector. In this embodiment, the displacement of the spot A  404 ′ is measured as a function of the entry pupil position. FIG. 5 illustrates such an embodiment. 
     In an alternate embodiment, an operation of the refractometer  400  is described as follows. In this embodiment, the spatial light pattern generator  402  is a spatial light modulator (SLM). A controller (not shown) switches on a plurality of light sources  404  from the SLM  402 . The plurality of light sources  404  form a predetermined pattern. Rays  405  from each light source  404  impinge on corresponding lenslets  410 . The distance between each light source  404  and each lenslet  410  is predetermined such that each beam  414  exiting each lenslet  410  is substantially collimated. 
     Each collimated beam  414  in the pattern next encounters the relay lenses  428  and  430 . In one preferred embodiment, the relay lenses  428  and  430  receive each collimated light beam  414  and transmit an inverted but otherwise substantially same collimated light beam  414 . 
     Each collimated beam  414 ′ in the pattern next encounters the eye  420 . The eye  420  includes a cornea  418 , a lens  419  and fluid  421  which all contribute to focusing each collimated beam  414 ′ onto the retina  412 . In this embodiment, each collimated beam  414 ′ is focused by the eye  420  to points on the retina  412  (not shown). The points on the retina  412  represents the light that has entered the eye  420  through those portions of the pupil  426  defmed by the images of the lenslets  410 . The points on the retina correspond to the pattern from the SLM  402 . 
     As different point sources from different locations on the SLM  402  are illuminated by a controller (not shown), the angle at which the light enters the eye  420  changes. This changes the position of the points A on the retina  412 . The SLM  402  projects a pattern of points onto the retina  412 . Using this technique, the aberrations in the system can be characterized. In one embodiment, a pattern of light sources in the SLM  402  is switched on by a controller (not shown), and corresponding locations of those light source images are formed on the retina  412 . An estimate of the wavefront aberration for the eye  420  is made by measuring the displacement of each of the light source images in the pattern from their ideal locations. In one embodiment, a camera is used to photograph the pattern on the retina. Skilled artisans will appreciate that other devices could be used such as charge coupled device (CCD) cameras, photosensitive film, array detectors, or the like. 
     In another embodiment, a reference pattern is projected, and the displacement of a projected measurement pattern from the reference pattern is measured. In yet another embodiment, the reference pattern is moved while the measurement pattern is observed. In these embodiments, a visual rendering of the retina is used. 
     FIG. 5 is a schematic block diagram of an illustrative wavefront sensor  500  for measuring characteristics of an eye  420  according to another embodiment of the invention. The wavefront sensor  500  is also referred to as a refractometer. The front surface  403  of the spatial light pattern generator  402  contains the light modulating elements  404  and  406 . That surface  403  is disposed in a plane perpendicular to axis Z of the refractometer  500 . The lenslet array  408  comprises a plurality of evenly spaced lenslets  410  arranged in a planar configuration. In one embodiment, the lenslets  410  are arranged in a matrix configuration. In another embodiment, the lenslets  410  are arranged in a radial configuration. In yet another embodiment, the positions of the lenslets  410  with respect to one another is varied. The light modulating elements  404  and  406  are located at a position corresponding to the focal length F of the lenslets  408 . In the illustrative embodiment, the refractometer  500  includes the relay lenses  428  and  430 . The relay lenses  428  and  430  are used to modify the working distance between the user&#39;s eye  420  and the refractometer  500 . Skilled artisans will appreciate that other relay systems including mirrors (not shown) may be utilized without deviating from the spirit of the invention. In one embodiment, the relay lenses  428  and  430  are located a suitable distance away from the lenslet array  408 . In another embodiment, the distance L between the relay lenses  428  and  430  is fixed. In yet another embodiment, the relay lenses  428  and  430  are the substantially the same. In the illustrative embodiment, the distance L between the relay lenses  428  and  430  affects a characteristic of the optical signal being relayed. 
     The refractometer  500  also includes beamsplitter  510 . The beamsplitter  510  passes the light rays from the rely lens  430  to the cornea  418 . The eye  420  focuses these rays onto the retina  412  at points A′  406 ′ and A  406 . The lens  502  images the points A′  406 ′ and A  406  onto the detector  506 . The beamsplitter  510  redirects at least a portion of the reflected light from the retina  412  to the lens  502 . The reflected light  414 ′ and  416 ′ corresponds to the points  404 ′ and  406 ′, respectively. In one embodiment, the detector  506  is an array detector. In another embodiment, the detector  506  is a camera. In another embodiment, the detector  506  is a quadrant detector. In yet another embodiment, the detector  506  is an array of individual detectors. In still another embodiment, the detector  506  is a retina from another eye (e.g., a doctor&#39;s eye). In yet another embodiment, the detector  506  is a light sensitive detector, such as a photodetector. In one embodiment, the detector  506  couples to the control electronics  504 . In another embodiment, the control electronics  504  includes a computer. The computer analyzes data generated by the refractometer  500 . In one embodiment, the SLM  402  also couples to the control electronics  504 . The control electronics  504  controls the output of the SLM  402 . The control electronics  504  processes spatial information about points  404 ′ and  406 ′ as detected by detector  506  with respect to points  404  and  406  from the SLM  402 . Since the control electronics  504  controls the SLM  402 , the control electronics  504  can precisely determine the relationship between the point sources  404  and  406  on the SLM  402  and the points  404 ′ and  406 ′ on the retina  412 , respectively. In other embodiments, the control electronics  504  provides the relationship data to contact lens fabrication equipment, ocular lens fabrication equipment, or surgical procedures  508 . The ocular lens fabrication equipment includes fabrication of intraocular lenses. The surgical procedures include laser eye surgery or any procedures which entail the shaping of the eye  420 . 
     The operation of the refractometer  500  will be described next. As previously described, the spatial light pattern generator  402  is a spatial light modulator (SLM). The SLM  402  is an array of light sources. The control electronics  504  switches on a single light source  404  from SLM  402 . Rays from the light source  404  impinge on the lenslet  410 . The focal length F, of lenslet  410  determines the distance between the light source  404  and the lenslet  410  such that the beam exiting lenslet  410  is substantially collimated. 
     The collimated beam  414  next encounters the relay lenses  428  and  430 . In this embodiment, the relay lenses  428  and  430  vary the working distance between the refractometer  500  and the user&#39;s eye  420 . In one preferred embodiment, the relay lenses  428  and  430  receive the collimated light beam  414  and transmit an inverted but otherwise substantially the same collimated light beam. The relayed collimated beam  414  next encounters the beamsplitter  510 . The beamsplitter  510  passes a portion of the relayed beam  414  to the eye  420 . The cornea  418 , the lens  419 , and the fluid  421  of the eye  420  focus the relayed beam  414  onto the retina  412  at the point A  404 ′. The point A  404 ′ on the retina  412  represents the light that has entered the eye  420  through a portion of the pupil defined by the image of the lenslet  410 . The point  404 ′ on the retina  412  acts as a virtual point source in the refractometer  500 . The lens  502  images the point  404 ′ onto the detector  506 . The location of the point  404 ′ on the detector  506  corresponds to the location of the point  404 ′ on the retina  412 . The detector  506  generates a signal having a spatial location. The control electronics  504  receives the signal from the detector  506 . 
     Next, the control electronics  504  switches on the single light source  406 . The rays from source  406  impinge on the lenslet  410  from a different source location than the rays from source  404 . The light source  406  is at a distance corresponding to the focal length F of the lenslet  410 . The lenslet  410  generates collimated beam  416  corresponding to the light source  406 . The collimated beam  416  encounters relay lenses  428  and  430 . The relay lenses  428  and  430  invert and relay the collimated beam  416 . The eye  420  focuses the relayed beam  416  to the point A′ 406 ′ on the retina  412 . As different point sources from different locations on the SLM  402  are illuminated by the control electronics  504 , the angle at which the light enters the eye  420  changes. This affects the position of the point of focus of that light on the retina  412 . The point  406 ′ on the retina  412  acts as a virtual point source in the refractometer  500 . The lens  502  images the point  406 ′ onto the detector  506 . The location of the point  406 ′ on the detector  506  corresponds to the location of point  406 ′ on the retina  412 . The detector  506  generates a signal having a spatial location. The control electronics  504  receives the signal from the detector  506 . 
     By knowing the location of each point source on the SLM  402  and the location of each virtual point source on the detector  506 , the control electronics  504  can calculate the location of each point source corresponding to an ideal eye  420 . The control electronics  504  sends the location of each point source corresponding to the ideal eye  420  to a lens fabrication system  508 . The lens fabrication system  508  uses the location data to generate a corrective lens. The corrective lens compensates for the optical aberrations of the eye  420 . In another embodiment, the control electronics  504  sends the location data to a surgical system  508 . The surgical system  508  uses the location data to reshape the eye  420 . The reshaping of the eye  420  corrects for the optical aberrations detected by the refractometer  500 . Hence, the aberrations of the eye  420  are characterized and corrected by exploiting this technique. In an alternate embodiment, the control electronics  504  sequentially switches on each light source in the SLM  402 , and a corresponding location of that light source image is formed on the retina  412 . 
     FIG. 6 is a block diagram of a wavefront sensor  600  for measuring the optical aberrations of a lens  618  according to an embodiment of the invention. The wavefront sensor  600 , in other embodiments, is used to characterize the aberrations in optical elements (i.e., mirrors) and optical systems (i.e., telescopes). The front surface  403  of the spatial light pattern generator  402  contains the light modulating elements  404  and  406 . The light modulating elements  404  and  406  are located at a position corresponding to the focal length F of the lenslets  408 . In the illustrative embodiment, the wavefront sensor  600  includes the relay lenses  428  and  430 . The relay lenses  428  and  430  modify the working distance between the user&#39;s eye  420  and the refractometer  400 . Skilled artisans will appreciate that other relay systems including mirrors (not shown) may be utilized without deviating from the spirit of the invention. In another embodiment, relay lenses  428  and  430  are not used at all (not shown). In yet another embodiment, a system designer locates the relay lenses  428  and  430  a suitable distance away from the lenslet array  408 . 
     The lens  618  will be described next. The perfect lens  618  receives light which is ideally focused onto a single point on the detector  506 . Refractive errors in the lens  618  affect the point of focus of the light. The lens  618  is located with respect to the refractometer  400  such that light exiting relay lens  430  will impinge on the lens  618  and be focused onto a point on the detector  506 . In one embodiment, the detector  506  is an array detector. In another embodiment, the detector  506  is a camera. In yet another embodiment, the detector  506  is a quadrant detector. In yet another embodiment, the detector  506  is an array of individual detectors. In yet another embodiment, the detector  506  is a light sensitive detector, such as a photodetector or a photodiode. 
     In one embodiment, the detector  506  couples to the control electronics  504 . The control electronics  504  includes a computer. The control electronics  504  receives data from the detector  506 . The data corresponds to the locations  604 ′ and  606 ′ on the detector  506 . The aberrations of lens  618  are determined by repeating this technique across the surface of lens  618 . The control electronics  504  compares location data from the spatial pattern generator  402  with location data form the detector  506 . The control electronics  504  uses the data to generate wavefront data. The wavefront data is a measure of the aberrations of lens  618 . In another embodiment, a mirror (not shown) replaces the lens  618 . In other embodiments, the mirror is a spherical mirror, a concave mirror, a convex mirror, an elliptical mirror, a planar mirror, a flexible mirror, or the like. 
     In yet another embodiment, the mirror is a segmented mirror for use with an adaptive optics system. One type of adaptive optics system is used to compensate for atmospheric effects on large telescopes such as temperature variations. In one embodiment, the large telescope uses a large mirror comprised of segmented portions. Each mirror portion couples to an actuator which controls the location of the mirror portion. The actuators couple to a processor. The processor determines the ideal position of each mirror portion and adjusts the actuators accordingly. In this embodiment, the refractometer  400  is used to adjust the mirror portions to “null” the aberrations of the segmented mirror. The control electronics  504  acquires knowledge of the ideal location of each mirror portion in the segmented mirror through the use of the refractometer  400  and the detector  506 . 
     One object of the wavefront sensor  600  is to measure the deviations of the wavefront surface from a plane. In the case of a telescope, for example, small temperature variations in the earth&#39;s atmosphere cause the light entering different parts of the telescope pupil to travel at slightly different speed, producing variations in the optical path. These variations in the optical path cause images of astronomical objects to become blurred. By measuring these path length differences across the telescope pupil, an adaptive optics system (such as that of FIG. 7) can correct them in real time using a segmented mirrors having a plurality of mirror portions or a flexible mirror. The adaptive optics system  700  sharpens the astronomical images. Since the atmosphere is constantly shifting, the adaptive optics system constantly adjusts to those shifts. The wavefront sensor  600  monitors these atmospheric shifts. In another embodiment, the wavefront sensor  600  inputs compensation values into the adaptive optics system  700 . 
     The operation of the wavefront sensor  600  will be described next. In one embodiment, the spatial light pattern generator  402  is a spatial light modulator (SLM). A single light source  404  from SLM  402  is switched on. Rays from the light source  404  impinge on the lenslet  410 . The distance between the light source  404  and the lenslet  410  is predetermined such that the beam  414  exiting the lenslet  410  is substantially collimated. This collimation occurs at a distance F, the focal length of the lenslet  410 . 
     The collimated beam  414  next encounters the relay lenses  428  and  430 . In this embodiment, relay lenses vary the working distance between the refractometer  400  and the lens  618 . In one preferred embodiment, the relay lenses  428  and  430  receive the collimated light beam  414  and transmit an inverted but otherwise substantially the same collimated light beam  414 ′. In another embodiment, the relay lenses  428  and  430  have different focal lengths. In that embodiment, the collimated beam  414  has a different diameter than the collimated beam  414 ′. Another embodiment employs pluralities of relay lens sets. A further embodiment employs suitable optical mirrors (not shown) to relay the collimated beam  414  to a desired location. Yet another embodiment utilizes a combination of relay lenses and mirrors. 
     The collimated beam  414 ′ next encounters the lens  618 . The lens  618  modifies an optical signal as it traverses the lens  618 . In the embodiment shown, the lens  618  is a focusing lens. In another embodiment the lens  618  is a diverging lens (not shown). In still other embodiments, a mirror (not shown) replaces the lens  618 . In yet another embodiment, a multiple element optical system (not shown) replaces the lens  618 . The point A  604 ′ on the detector  506  represents the light that has entered the lens  618  through a portion of the lens  618  defined by the image of the lenslet  410 . Next, the point source  406  is switched on. The rays from that point source impinge on the lenslet  410  from a different source location than the rays from the point source  404 . 
     The point source  406  is at a distance corresponding to the focal length F of the lenslet  410 . The lenslet  410  generates the collimated beam  416  corresponding to the light source  406 . The collimated beam  416  encounters the relay lenses  428  and  430 . The relay lenses  428  and  430  invert and relay the collimated beam  416  to generate the collimated beam  416 ′. The collimated beam  416 ′ enters the lens  618  at the same location as the collimated beam  414 ′. The lens  618  focuses the collimated beam  416 ′ to the point A′  406 ′ on the detector  506 . As the control electronics  504  switches on different point sources from different locations on the SLM  402 , the angle at which the light enters the lens changes corresponding to the locations of the illuminated point sources. These angles change the position of the point A on the detector  506 . 
     The aberrations in the system can be characterized by exploiting this technique. In one embodiment, the control electronics  504  sequentially switches on each light source in the SLM  402 , which forms an image at a corresponding location of that light source on the detector  506 . Changing the position of the light source changes the angle at which the light enters the lens  618 . The control electronics  504  sequentially switches on various light sources from the SLM  402  until one light source aligns with a reference location on the detector  506 . The position of that light source corresponds to the angle in which the light was required to bend through the lens  618  to contact the reference location on the detector  506 . By mapping the location of the light source versus the position of the image on the detector  506 , the characteristics of the wavefront aberration of the lens  618  are realized. This is accomplished by making successive measurements across each lenslet  410  in the lenslet array  408 . The measurements generate a set of light entry angles for the lens  618 . An estimate of the wavefront aberration for the lens  618  is readily computed by the control electronics  504  from the set of light entry angles. In one embodiment, the control electronics  504  includes a computer or a processor. 
     FIG. 7 shows one illustrative achievement of the invention. FIG. 7 illustrates an adaptive optics system  700  for projecting a diffraction limited image  406 ″ according to one embodiment of the invention. In the embodiment shown, the system  700  projects a diffraction limited image  406 ″ on the retina  412  of the eye  420 . In other embodiments, the system  700  projects a diffraction limited image  406 ″ onto a detector, a camera, a charge coupled device (CCD) detector, or the like. In other embodiments, a lens, a mirror, or other optical element replaces the eye  420 . Skilled artisans will appreciate the myriad of uses for the adaptive optics system  700  of the present invention, including, for example, compensating for atmospheric effects in telescopes. 
     The adaptive optics system  700  utilizes the same components from the refractometer  400  in a different manner. The front surface  403  of the spatial light pattern generator  402  contains the light modulating elements  404 ,  401  and  409 . In one embodiment, the surface  403  can be disposed in a plane perpendicular to axis Z of the refractometer  400 . The lenslet array  408  comprises a plurality of evenly spaced lenslets  410 ,  410 ′ and  410 ″ arranged in a planar configuration. In another embodiment, the lenslet array  408  can be disposed in the plane perpendicular to axis Z of the refractometer  400 . The system designer locates the light modulating elements  404 ,  401  and  409  at a position corresponding to the focal length F of the lenslets  408 . In the illustrative embodiment, the refractometer  400  includes the relay lenses  428  and  430 . The relay lenses  428  and  430  modify the working distance between the user&#39;s eye  420  and the refractometer  400 . Skilled artisans will appreciate that other relay systems including mirrors (not shown) may be utilized without deviating from the spirit of the invention. The system designer positions the relay lenses  428  and  430  in the plane perpendicular to the Z-axis of the refractometer  400 . In the illustrative embodiment, the optical axes of the relay lenses  428  and  430  correspond to the Z-axis. In another embodiment, the system designer locates the relay lenses  428  and  430  a suitable distance away from the lenslet array  408 . 
     The operation of adaptive optics system  700  will be described next. In one embodiment, the spatial light pattern generator  402  is a spatial light modulator (SLM). In another embodiment, the spatial light pattern generator  402  comprises a plurality of coherently related point sources arranged in an array configuration. In yet another embodiment, the spatial light pattern generator  402  comprises a uniform light source  232  of the configuration shown in FIG.  2 F. 
     The refractometer  400  operates in the same manner as described with reference to FIG.  4 . The refractometer  400  determines the locations of the point sources  404 ,  401 , and  409  on the spatial light pattern generator  402  corresponding to the wavefront aberrations of the eye  420 . A suitable number of point sources from the spatial light pattern generator  402  are illuminated by a controller (not shown) based on the desired resolution. Once the refractometer  400  determines the proper spatial locations of the point sources from the spatial light pattern generator  402 , the adaptive optics system  700  utilizes the location data. As an illustrative example, the controller (not shown) illuminates the point sources  404 ,  401 , and  409  on the spatial light pattern generator  402  in sites corresponding to a wavefront aberration compensated eye  420 . When illuminated, the light from each point source  404 ,  401 , and  409  focuses on the same spot  406 ″ on the retina  412 . In one embodiment, the point sources  404 ,  401 , and  409  are coherent with respect to one another. 
     The controller illuminates a single light source  404  from the spatial light pattern generator  402 . Rays from point source  404  impinge on lenslet  410 . The distance between point source  404  and lenslet  410  corresponds to the focal length F of the lenslet  410  such that the beam  414  exiting lenslet  410  is substantially collimated. The collimated beam  414  next encounters relay lenses  428  and  430 . In one preferred embodiment, the relay lenses  428  and  430  receive the collimated light beam  414  and transmit an inverted but otherwise substantially the same collimated light beam  414 ′. The collimated beam  414 ′ next encounters the eye  420 . In the illustrative embodiment, the eye  420  focuses the collimated beam  414 ′ to the point  406  on the retina  412 . The point  406 ″ on the retina  412  represents the light that has entered the eye  420  through a portion of the pupil defined by the image of the lenslet  410 . Since the point source  404  is at a location corresponding to the compensated wavefront, the eye  420  focuses the collimated beam  423 ′ to the point  406 ″ on the retina  412 . 
     Next, the controller switches on a single light source  401  from spatial light pattern generator  402 . Rays from point source  401  impinge on lenslet  410 ′. The distance between point source  401  and lenslet  410 ′ is predetermined such that the beam  411  exiting lenslet  410  is substantially collimated. Collimated beam  411  next encounters the relay lenses  428  and  430 . In the preferred embodiment, relay lenses  428  and  430  receive the collimated light beam  411  and transmit an inverted but otherwise substantially the same collimated light beam  411 ′. The collimated beam  411 ′ next encounters the eye  420 . In the illustrative embodiment, the eye  420  focuses the collimated beam  411 ′ to the point  406 ″ on the retina  412 . The point  406 ″ on the retina  412  represents the light that has entered the eye  420  through a portion of the pupil defined by the image of the lenslet  410 ′. Since the point source  401  is at a location corresponding to the compensated wavefront, the eye  420  focuses the collimated beam  411 ′ to the point  406 ″ on the retina  412 . 
     Next, the controller switches on another single light source  409  from spatial light pattern generator  402 . Rays from point source  409  impinge on lenslet  410 ″. The distance between point source  409  and lenslet  410 ″ is predetermined such that the beam  419  exiting lenslet  410 ″ is substantially collimated. Collimated beam  419  next encounters relay lenses  428  and  430 . In the preferred embodiment, relay lenses  428  and  430  receive the collimated light beam  419  and transmit an inverted but otherwise substantially the same collimated light beam  419 ′. The collimated beam  419 ′ next encounters the eye  420 . In the illustrative embodiment, the eye  420  focuses the collimated beam  419 ′ to the point  406 ″ on the retina  412 . The point  406  on the retina  412  represents the light that has entered the eye  420  through a portion of the pupil defined by the image of the lenslet  410 ″. Since the point source  409  is at a location corresponding to the compensated wavefront, the eye  420  focuses the collimated beam  419 ′ to the point  406 ″ on the retina  412 . 
     Once a set of compensated point sources on the spatial light pattern generator  402  is defmed, each point source is precisely imaged at a point  406 ″ on the retina  412 . By switching on all of the compensated point sources at once, the resultant image on the retina depends on the coherence relationship between the points. If the point sources are incoherently related, then the image on the retina  412  is a superposition of blurred circles corresponding to each of the lenslets  410  in the lenslet array  408 . If the point sources are coherently related, that is, if each point source emits light of the same wavelength and phase, the points imaged on the retina  412  add coherently. In that case, the spot size on the retina is equivalent to the spot size of the entire pupil of the eye  420 . Hence, a diffraction limited spot for the entire pupil is realized. 
     In one embodiment, emission of coherent light is achieved through the use of programmable actuated mirrors. Illuminating the mirrors with a laser and selecting the appropriate mirrors to actuate generates a spatial light pattern. Each point in the spatial light pattern emits light of the same wavelength and phase. 
     In one embodiment, the adaptive optics system  700  of the invention compensates for the aberrations in a lens, such as a telescope objective. In another embodiment, the adaptive optics system compensates for the aberrations in a multiple element optical component. In yet another embodiment, the adaptive optics system  700  compensates for the aberrations in a mirror. 
     One contemplated use for the adaptive optics system  700  is by optometrists or eye surgeons. Eye surgeons can use the adaptive optics system  700  to illustrate the expected postsurgery improvement in a patient&#39;s vision. This “try before you buy” system  700  enables patients to decide whether the improvement in their vision is worth undergoing the surgery. The operation of the system  700  is as follows. A patient considering eye surgery for vision improvement looks into an eye input port (not shown) in the system  700 . The system  700  reveals an image to the patient. Selecting specific point sources on the spatial light pattern generator  402  forms a diffraction limited spot on the retina  420 . The system then scans the diffraction limited spot across the pupil  426  of the eye  420  creating the image viewed by the patient. If the patient&#39;s eye  420  is imperfect, the patient sees an image which is blurred. The system  700  then performs a series of measurements across the surface of the eye  420  to determine the wavefront aberrations of the eye  420 . The system  700  uses that data to determine which point sources on the spatial light pattern generator  402  are required to bring the image into focus for the eye  420 . The controller illuminates those point sources, and the patient sees an improvement in the focus of the image. If the improvement is not adequate, the patient can decide to forego the surgery. By compensating for the wavefront aberrations of the eye, the system  700  precisely models the result of a laser reshaping the eye. In some cases, reshaping of the eye through the use of a laser or other means does not result in sufficient vision improvement. In those cases, the system  700  spares the patient the risk, time, expense, pain, and recovery of the surgery. 
     In another embodiment, the adaptive optics system  700  generates a single, diffraction limited spot on the retina  412 . In another embodiment, the adaptive optics system  700  generates a single, diffraction limited spot on an image plane or a detector (not shown). In yet another embodiment, the adaptive optics system  700  generates a high-resolution image of the retina  412 . The high-resolution image is achieved, in one embodiment, by using the scanning system illustrated in FIG.  8 . 
     FIG. 8 illustrates a retinal scan system for obtaining a high-resolution image of the retina according to an embodiment of the invention. The scan system of FIG. 8 uses concepts described with respect to the adaptive optics system of FIG.  7 . FIG. 8 includes components described in FIG. 7 as well as a scanning device  802 . The scanning device  802  is used to move the diffraction limited spot  406 ″ across the pupil  426  to create the high resolution image of the retina  412 . In one illustrative embodiment, a scanning device  804  includes the relay lenses  428 ,  430 ,  430 ′ and  428 ′. In other embodiments, the scanning device  804  includes other relay mechanisms and optical components (not shown). Skilled artisans will appreciate that scanning devices suitable for use with the invention are commonly available. In one embodiment, the system  800  projects the diffraction limited image  406 ″onto the retina  412  of the eye  420 . In other embodiments, the system  800  projects the diffraction limited image  406 ″ onto a detector, a camera, a charge coupled device (CCD), or the like. 
     The components of FIG. 8 will be described next. The front surface  403  of the spatial light pattern generator  402  contains the light modulating elements  404 ,  401  and  409 . The lenslet array  408  comprises a plurality of evenly spaced lenslets  410 ,  410 ′ and  410 ″ arranged in a planar configuration. The light modulating elements  404 ,  401  and  409  are disposed at a location corresponding to the focal length F of the lenslet array  408 . In the illustrative embodiment, the system further includes the relay lenses  428  and  430 , a scanning device  802 , and the relay lenses  430 ′ and  428 ′. The relay lenses  428 ,  430 ,  430 ′ and  428 ′ modify the working distance between the user&#39;s eye  420  and the system  800 . Skilled artisans will appreciate that other relay systems including mirrors (not shown) may be utilized without deviating from the spirit of the invention. It will also be appreciated by skilled artisans that the system  800  can include both sets of relay lenses, one set of relay lenses, or no relay lenses at all. In one embodiment, the relay lenses are integrated as part of the scanning device  804 . In one embodiment, the system  800  also includes a beamsplitter  510  and a detector  506 . In another embodiment (not shown), the beamsplitter  510  is located to the right of the spatial pattern generator  402  in the system  800 . This embodiment ensures that the detector receives aberration-compensated rays that travel back through the system  800  from the retina  412 . In other embodiments, the detector  506  is a quadrant detector, a charge coupled device (CCD) detector, a camera, photosensitive film, or the like. In another embodiment, the system  800  also includes control electronics  504 . In yet another embodiment, the control electronics  504  includes a computer. 
     The operation of adaptive scan system  800  will be described next. In one embodiment, the spatial light pattern generator  402  is a spatial light modulator (SLM). In another embodiment, the spatial light pattern generator  402  comprises a plurality of coherently related point sources arranged in an array configuration. In yet another embodiment, the spatial light pattern generator  402  comprises a uniform light source  232  of the configuration shown in FIG.  2 F. In one embodiment, the uniform light source  232  is a laser. 
     The system  800  determines the locations of the point sources  404 ,  401 , and  409  on the spatial light pattern generator  402  corresponding to the wavefront aberrations of the eye  420 . A suitable number of point sources from the spatial light pattern generator  402  are illuminated based on the desired resolution. Once the system  800  determines the proper spatial locations of the point sources from the spatial light pattern generator  402 , the system  800  utilizes the location data. As an illustrative example, the point sources  404 ,  401 , and  409  are positioned on the spatial light pattern generator  402  in sites corresponding to a wavefront aberration compensated eye  420 . When illuminated, the light from each point source  404 ,  401 , and  409  focuses on the same spot  406 ″ on the retina  412 . The point sources  404 ,  401 , and  409  are coherent with respect to one another. 
     The control electronics  504  illuminates a single light source  404  from the spatial light pattern generator  402 . Rays from point source  404  impinge on lenslet  410 . The distance between point source  404  and lenslet  410  is such that the beam  414  exiting lenslet  410  is substantially collimated. The collimated beam  414  next encounters relay lenses  428  and  430 . In one preferred embodiment, the relay lenses  428  and  430  receive the collimated light beam  414  and transmit an inverted but otherwise substantially the same collimated light beam  414 ′. The collimated beam  414 ′ next encounters the scanning device  802 . In one embodiment, the scanning device  802  comprises a movable mirror for directing the collimated beam  414 ′ to different locations across the pupil  426 . Skilled artisans will appreciate that other embodiments of scanning devices  802 , such as a galvanometer, can be used. In the illustrative embodiment, the collimated beam  414 ′ next encounters relay lenses  430 ′ and  428 ′. In one preferred embodiment, the relay lenses  430 ′ and  428 ′ receive the collimated light beam  414 ′ and transmit an inverted but otherwise substantially the same collimated light beam  414 ″. The collimated light beam  414 ″ next encounters the eye  420 . The eye  420  focuses the collimated beam  414 ′ to the point  406 ″ on the retina  412 . The point  406 ″ on the retina  412  represents the light that has entered the eye  420  through a portion of the pupil defmed by the image of the lenslet  410 . Since the point source  404  is at a location corresponding to the compensated wavefront, the eye  420  focuses the collimated beam  414 ′ to the point  406 ″ on the retina  412 . 
     Next, the control electronics  506  switches on a single light source  401  from the spatial light pattern generator  402 . Rays from point source  401  impinge on lenslet  410 ′. The distance between point source  401  and lenslet  410 ′ is the focal length F of lenslet  410 ′. Hence, beam  411  exiting lenslet  410  is substantially collimated. Collimated beam  411  next encounters the relay lenses  428  and  430 . In the preferred embodiment, relay lenses  428  and  430  receive the collimated light beam  411  and transmit an inverted but otherwise substantially the same collimated light beam  411 ′. The collimated beam  411 ′ next encounters the scanning device  802 . The scanning device  802  transmits the collimated beam  411 ′ to the relay lenses  430 ′ and  428 ′. Relay lenses  430 ′ and  428 ′ transmit an inverted but otherwise substantially the same collimated beam  411 ″. The collimated beam  411 ″ next encounters the eye  420 . In the illustrative embodiment, the eye  420  focuses the collimated beam  411 ″ to the point  406 ″ on the retina  412 . The point  406 ″ on the retina  412  represents the light that has entered the eye  420  through a portion of the pupil defined by the image of the lenslet  410 ′. Since the point source  401  is at a location corresponding to the compensated wavefront, the eye  420  focuses the collimated beam  411 ′ to the point  406 ″ on the retina  412 . 
     Next, the control electronics  506  switches on another single light source  409  from the spatial light pattern generator  402 . Rays from point source  409  impinge on lenslet  410 . The distance between point source  409  and lenslet  410 ″ is the focal length F of lenslet  410 ″. Hence, beam  423  exiting lenslet  410 ″ is substantially collimated. Collimated beam  423  next encounters the relay lenses  428  and  430 . In the preferred embodiment, relay lenses  428  and  430  receive the collimated light beam  423  and transmit an inverted but otherwise substantially the same collimated light beam  423 ′. The collimated beam  423 ′ next encounters the scanning device  802 . The scanning device  802  transmits the collimated beam  423 ′ to the relay lenses  430 ′ and  428 ′. Relay lenses  430 ′ and  428 ′ transmit an inverted but otherwise substantially the same collimated beam  423 ″. The collimated beam  423 ″ next encounters the eye  420 . In the illustrative embodiment, the eye  420  focuses the collimated beam  423  to the point  406 ″ on the retina  412 . The point  406 ″ on the retina  412  represents the light that has entered the eye  420  through a its portion of the pupil defined by the image of the lenslet  410 ″. Since the point source  401  is at a location corresponding to the compensated wavefront, the eye  420  focuses the collimated beam  423 ″ to the point  406 ″ on the retina  412 . 
     Once a set of compensated point sources on the spatial light pattern generator  402  is defined, each point source is precisely imaged at a point  406 ″ on the retina  412 . When the control electronics  504  switches on all of the compensated point sources at once, the resultant image on the retina depends on the coherence relationship between the points. If the point sources are incoherently related, then the image on the retina  412  is a superposition of blurred circles corresponding to each of the lenslets  410  in the lenslet array  408 . If the point sources are coherently related, that is, if each point source emits light of the same wavelength and phase, the points imaged on the retina  412  add coherently. In that case, the spot size on the retina is equivalent to the spot size of the entire pupil of the eye  420 . Hence, a diffraction limited spot for the entire pupil is realized. 
     The point  406 ″ on the retina  412  generated by point sources  404 ,  401 , and  409  acts as a virtual point source to detector  506 . In one embodiment, rays from the virtual point source  406 ″ traverse the system  800  and impinge on detector  506  as a point  406 ′″. In one embodiment, the virtual point source  406 ″ traverses the pupil  426  of the imperfect eye  420 . The aberrations of the eye  420  cause the detected point  406 ′″ to blur on the detector  506 . In another embodiment, the system  800  includes additional components (not shown) which compensate for the blur on the detector  506 . 
     In one embodiment, emission of coherent light from the spatial light pattern generator  402  is achieved through the use of programmable actuated mirrors. Illuminating the mirrors with a laser and selecting the appropriate mirrors to actuate generates a spatial light pattern. In this embodiment, each point in the spatial light pattern emits light of the same wavelength and phase. Skilled artisans will appreciate the myriad of methods available to generate coherent light having a defined spatial pattern. 
     Once the system  800  generates the point  406  on the retina  412 , that point generates collimated beams  414 ′″,  411 ′″ and  423 ′″. Beamsplitter  510  redirects collimated beams  414 ′″,  411 ′″ and  423 ′″ to lens  502 . Lens  502  focuses beams  414 ′″,  411 ′″. and  423 ′″ onto detector  506  as point  406 ′″. 
     The control electronics  504  controls the scanning device  802 . In one embodiment, the scanning device  802  performs a raster scan causing the point  406 ″ to move across the retina  412 . As the point  406 ″ moves across the retina, the corresponding point  406 ′″ moves across the surface of the detector  506 . By choosing a sufficient number of scanned points a high-resolution image of the retina  412  can be realized. 
     In one embodiment, the control electronics  504  includes a computer. The computer controls the spatial light pattern generator  402 , the detector  506 , and the scanning device  802 . In another embodiment, the computer generates a high-resolution image of the retina  412  based on the detected points  406 ′″. In another embodiment, the patient observes an aberration compensated image generated by the scanned points  406 ″. The aberration compensated image corresponds to the image a patient can expect post-surgery. The system  800  enables patients to decide whether the improvement in their vision is worth undergoing the surgery. 
     The operation of the system  800  is as follows. A patient considering eye surgery for vision improvement looks into an eye input port (not shown) in the system  800 . The system  800  reveals an image to the patient. Selecting specific point sources on the spatial light pattern generator  402 , and scanning those points across the pupil  426  forms an image on the retina  420 . If the patient&#39;s eye  420  is imperfect, the patient sees an image which is blurred. The system  800  then performs a series of measurements across the surface of the eye  420  to determine the wavefront aberrations of the eye  420 . The system  800  uses that data to determine which point sources on the spatial light pattern generator  402  are required to bring the image into focus for the eye  420 . The control electronics  504  illuminated those compensated point sources, and the patient sees an improvement in the focus of the image. If the improvement is not adequate, the patient can decide to forego the surgery. By compensating for the wavefront aberrations of the eye, the system  800  precisely models the result of a laser reshaping the eye. In some cases, reshaping of the eye through the use of a laser or other means does not result in sufficient vision improvement. In those cases, the system  800  spares the patient the risk, time, expense, pain, and recovery of the surgery. 
     Having described and shown the preferred embodiments of the invention, it will now become apparent to one of skill in the art that other embodiments incorporating the concepts may be used and that many variations are possible which will still be within the scope and spirit of the claimed invention. It is felt, therefore, that these embodiments should not be limited to disclosed embodiments but rather should be limited only by the spirit and scope of the following claims.