Abstract:
A system and method for stabilizing an eye includes a contact element that is placed in contact with the anterior surface of the eye. The purpose here is to oppose movements of the eye during an ophthalmic surgical procedure. Importantly, while it is in contact with the eye, the contact element is positioned to exert minimal pressure on the eye. This is done to avoid causing any deformations of the eye that might otherwise adversely compromise a laser beam during the ophthalmic surgery.

Description:
[0001]    This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/467,263, filed Mar. 24, 2011. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention pertains generally to systems and methods for performing ophthalmic surgery. More particularly, the present invention pertains to systems and methods for stabilizing an eye during ophthalmic surgery. The present invention is particularly, but not exclusively, useful as a system and method that stabilizes the eye with a contact element while causing minimal changes in refractive properties of the eye during ophthalmic surgery. 
       BACKGROUND OF THE INVENTION 
       [0003]    Surgical lasers are now commonly used in a variety of ophthalmic surgical procedures, including the treatment of ocular diseases and the correction of optical deficiencies. In these procedures, the surgical laser is often chosen as the tool of choice because of the ability of the laser to be accurately focused with great precision. In addition, the ability of the laser to be guided to designated locations within the eye, with precision and reliability, has enabled ophthalmic procedures to be performed throughout the eye. 
         [0004]    Anatomical characteristics of the eye, however, can undermine the effectiveness of any laser procedure. In particular, this is so for ophthalmic laser surgery that is to be performed on tissue behind (i.e. posterior) the cornea. Specifically, the beam of a laser can be significantly degraded by wrinkles that may be induced predominantly on the posterior surface of the cornea of an eye, when the eye is being stabilized by a contact element. The effect of these wrinkles becomes most acute when the laser beam is used for procedures on tissues in the deeper regions of the eye beyond the cornea, such as the lens or the retina. 
         [0005]    Typically, when an eye stabilizing device is used, it is placed against the anterior surface of the eye and is pressed in a posterior direction. As a consequence, tissue in the eye may be squeezed in a manner that will cause wrinkles to be created primarily on the posterior surface of the cornea of the eye. These wrinkles can then cause an undesirable refraction, dispersion and degradation of the laser beam, as well as other adverse optical effects, as it passes through the cornea. An additional drawback caused by dispersion of the laser beam is the possibility of unintentionally damaging non-targeted tissue. 
         [0006]    In light of the above, it is an object of the present invention to stabilize the eye for a laser surgical procedure with a contact element that avoids changing the refractive properties of the eye. Another object of the present invention is to properly position a contact element to minimize the distortion and degradation of a laser beam as it travels through the cornea to perform an ophthalmic procedure on tissue in the eye, particularly beyond the cornea. Yet another object of the present invention is to provide a device and method for stabilizing the eye during an ophthalmic procedure that is easy to use, is relatively simple to manufacture, and is comparatively cost effective. 
       SUMMARY OF THE INVENTION 
       [0007]    In accordance with the present invention, a system and method are provided for stabilizing an eye which require physically restraining movements of an eye in orthogonal x-y-z directions. The essential purpose here is to stabilize the eye, or some other transparent object made of a resilient material, while preventing any distortion of the eye (object) that will substantially change its refraction or refractive properties. For the present invention, this is done by juxtaposing the contact surface of a contact element against a selected surface of the eye (object) and establishing an operational location for the contact element relative to the eye. More specifically, with the contact element in its operational location there will be minimal, if any, contact pressure on the eye and, thus, unwanted distortions of the eye are effectively obviated. 
         [0008]    Structurally, in order to establish a proper juxtaposition of the contact element, the contact surface is shaped with a substantially matching (i.e. mating) correspondence to the selected surface of the eye (object). For example, in a preferred embodiment of the present invention, the contact surface will be substantially concave, and the selected surface (e.g. the anterior surface of the cornea of the eye) will be substantially convex. 
         [0009]    In addition to the contact element, the system includes a detector for monitoring an interaction between the contact element and the object. As intended for the present invention, one purpose of the detector is to establish and maintain an operational location for the contact element that will oppose movements of the eye (object). Another purpose of the detector is to generate a position signal that indicates an interaction between the contact element and the object, and that can be used by the system to ensure proper positioning of the contact element onto the eye. For the present invention, the detector may be either a pressure sensor, or an imaging unit. 
         [0010]    In an embodiment of the system wherein the detector is a pressure sensor, the detector can be of any type well known in the pertinent art. Preferably, it will be mounted directly on the contact element. The operational location of the contact element can then be established whenever the contact element is pressed against the eye and a pressure reading, or position indicator, from the detector attains a predetermined value. As will be appreciated by a skilled artisan, this predetermined value will typically be based on various characteristic factors of the eye (object), such as surface topography, shape and type of material. 
         [0011]    For an embodiment of the system wherein the detector is an imaging unit, the imaging unit will typically include a light source and a detector. For example, the present invention envisions OCT or Scheimpflug imaging. In any event, the light source will be used for directing an imaging light beam to both the contact element and to the eye (object). The imaging unit includes a receiving unit that will then receive light that is reflected from the contact element and from the object, and it will use this light to image the interaction between the contact element and the eye (object). Based on images of this interaction, the operational location of the contact element is established as being either: 1) when the eye (object) attains a predetermined shape after placement of the contact element (e.g. when a smooth posterior corneal surface is achieved); or 2) when the contact element makes initial contact with the eye (object). In both cases, the image can be used to determine when the distance between the contact element and the eye is equal to zero. For this embodiment, the contact element is preferably made of optical grade glass or a clear plastic material. 
         [0012]    It will be appreciated by the skilled artisan that the present invention lends itself to feedback control during the placement of the contact element. When feedback control is used, a computer and a controller are provided to cooperatively establish the contact element in its proper location on the eye. To do this, the detector produces an image or some other indication (e.g. pressure reading) of the interaction between the contact element and the eye (object). This data is then communicated to the computer. Upon receipt of this data, the computer compares the data with a reference input. Specifically, the reference input will be the predetermined pressure value when a pressure sensor is used as the detector, and it will be imaging data (i.e. images) when an imaging unit is used as the detector. If the computer calculates a deviation when comparing the reference input with the position signal, an error signal is generated. When an error signal is generated, the controller will move the placing device to position the contact element at its operational location, which minimizes the deviation to establish the error signal as a null. 
         [0013]    As an added feature of the present invention, a liquid can be deposited on the selected surface of the eye (object) prior to a juxtaposition of the contact element with the selected surface. Specifically, this can be done to buffer the interaction between the contact element and the object and further to equalize the pressure exerted by the contact element on the eye. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a schematic presentation of a system for the present invention, wherein a contact element has been juxtaposed against the eye of a patient; 
           [0015]      FIG. 2  is a cross sectional view of the contact element of the present invention in position relative to an eye of a patient as seen along line  2 - 2  in  FIG. 1 ; 
           [0016]      FIG. 3  is a cross sectional view of the contact element as shown in  FIG. 2  when the contact element exerts excessive pressure on an eye causing undesirable changes to the refractive properties of the cornea; 
           [0017]      FIG. 4  is a cross-sectional view of the contact element as shown in  FIG. 2  with an imaging unit being used for an operational placement of the contact element against the eye; and 
           [0018]      FIG. 5  is a cross-sectional view of the contact element as shown in  FIG. 2  with a pressure sensor being used for an operational placement of the contact element against the eye. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0019]    Referring initially to  FIG. 1 , a system for minimizing refractive index change in an eye (work piece) during an ophthalmic laser surgical procedure (alteration of the work piece) is shown and is generally designated  10 . As shown, the system  10  includes a table (chair)  12  for supporting a patient  14  during an ophthalmic surgical laser procedure. The system  10  also includes a laser unit  16  for performing the surgical laser procedure. Further, system  10  includes a controller  18  for operating the laser unit  16 , and it includes a computer  20  that provides instructions for an operation of the controller  18 . 
         [0020]      FIG. 1  also indicates that the computer  20  functions in response to a reference input  22 , and that the computer  20  also receives input from a detector  24 . More specifically, the detector  24  provides information to the computer  20  that pertains to the interactive relationship between a contact element  26  and the patient  14 . In particular, this interactive relationship is monitored as the contact element  26  is moved by a placement device  28  (i.e. a device for placing) into contact with an eye  30  of the patient  14 . The purpose here is to establish an operational relationship between the contact element  26  and the eye  30  that will stabilize the eye  30  during an ophthalmic laser procedure, without causing unwanted distortions of the eye  30 . 
         [0021]    The structural details of the contact element  26  will perhaps be best appreciated with reference to  FIG. 2 . There it will be seen that the contact element  26  includes a base  32 , with a contact lens  34  that is mounted on the base  32 . In detail, the contact lens  34  will typically have a contact surface  36  that substantially conforms to the shape of the anterior surface  38  of the eye  30 . It is to be appreciated that this conformity (i.e. correspondence) will differ from patient to patient and, therefore, it may be desirable, but not necessarily mandatory, to customize the contact element  26  for a particular patient  14 . Further, in order to be operationally compatible with the laser unit  16 , it is envisioned that the contact lens  34  of the contact element  26  will preferably be made of either an optical grade glass of a clear medical grade plastic. 
         [0022]    In an operation of the system  10 , the objective is to prevent a condition such as is shown in  FIG. 3 , wherein wrinkles  40  are formed on the posterior surface  42  of the cornea  44 . As indicated earlier, the avoidance of wrinkles  40  helps ensure the maximum operational capability of the laser unit  16 . For the present invention, this is accomplished by monitoring the interaction between the contact element  26  and the anterior surface  38  of the eye  30 , as the contact element  26  is being placed (juxtaposed) onto the eye  30 . 
         [0023]    Operationally, the system  10  monitors a distance “d” that is measured between the contact element  26  and the anterior surface  38  of the eye  30  (see  FIG. 2 ). For purposes of the present invention, because the contact surface  36  of the contact lens  34  is shaped to substantially conform to the anterior surface  38  of the eye  30 , the distance “d” will be substantially the same at every point on the anterior surface  38 . In the eventuality that there may be detectable differences in the distance “d” between the contact lens  34  and eye  30 , as it is measured between the contact surface  36  and the anterior surface  38 , a fluid film (not shown) can be employed between the contact surface  36  and the anterior surface  38  to obviate the differences. In any event, the detector  24  is used to measure the distance “d”, and to then provide this information to the computer  20 . With information about the distance “d”, the computer  20  compares this information with the reference input  22 . Based on this comparison, the computer  20  defines an error signal that is dependent on the distance “d”. Using well known closed loop feedback control techniques, the computer  20  then directs the controller  18  to move the laser unit  16 , and the placement device  28 , for placement of the contact element  26  into its operational location. For purposes of the present invention, the operational location of the contact element  26  is established when the contact surface  36  of the contact lens  34  is juxtaposed with the anterior surface  38  of the eye  30  (i.e. d=0), and the condition of the posterior surface  42  of the eye  30  shown in  FIG. 3  is avoided (i.e. there are no wrinkles  40 , or other structural distortions of the eye  30 ). In accordance with the present invention, this can be accomplished in either of two ways. For one, the detector  24  can be used as an inquiry unit. For another, the detector  24  can be used to detect pressures. 
         [0024]    With reference to  FIG. 4 , and with cross reference back to  FIG. 2 , an embodiment for the system  10  is indicated wherein the detector  24  is an imaging unit. More specifically, for purposes of the present invention, an imaging system for use as the detector  24  can be of any type well known in the pertinent art, such as devices that employ techniques of Optical Coherence Tomography (OCT), Scheimpflug, two-photon imaging, wavefront analysis and non-optical techniques such as acoustical imaging. Regardless of type, however, the detector  24  is used to operationally observe the distance “d” (e.g. as shown in  FIG. 2 ) and indicate when the distance “d” equals zero (e.g. when there is contact between the contact element  26  and the eye  30  as shown in  FIG. 4 ). In detail, when d=0, the embodiment of system  10  that includes an “imaging” type detector  24  can react and indicate achievement of an operational location for the contact element  26  in either of two circumstances. For one, the operational location can be established for contact element  26  by reference input  22  when an image created by the detector  24  indicates that “d” is actually zero. For another, again based on a reference input  22 , the operational location can be established for contact element  26  when an image indicates there has been a predetermined change in the shape of the cornea  44  of the eye  30 . 
         [0025]    With reference to  FIG. 5 , and with cross reference back to  FIG. 2 , an embodiment for the system  10  is indicated wherein the detector  24  is a “pressure activated” type detector  24 . For this embodiment, a pressure sensor  46  is employed. Preferably, the pressure sensor  46  will be of a type well known in the pertinent art, and it will be mounted on the contact element  26  for contact with the anterior surface  38  of the cornea  44 . In this case, the operational location for contact element  26  is established when the pressure sensor  46  indicates that the predetermined value for pressure of the contact element  26  against the anterior surface  38  of the cornea  44  has been attained. As implied above, the detector  24  can also respond as a position indicator when the pressure sensor  24  reacts with a movement to the interaction of the contact lens  34  with the eye  30 . 
         [0026]    It will be appreciated by the skilled artisan that a buffering fluid can be positioned on the anterior surface  38  of the eye  30  to distribute the interaction of the contact element  26  with the eye  30 . This fluid (not shown) can be used for either embodiment of the present invention. 
         [0027]    While the particular Apparatus and Method for Control of Refractive Index Changes in a Material as herein shown and disclosed in detail is fully capable of obtaining the objects and providing the advantages herein before stated, it is to be understood that it is merely illustrative of the presently preferred embodiments of the invention and that no limitations are intended to the details of construction or design herein shown other than as described in the appended claims.