Abstract:
The design of a corrective lens combines the measured aberration with decentration and rotation of the lens to design customized optical surface profiles to reliably achieve vision correction.

Description:
REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a continuation of International Patent Application No. PCT/US2013/022507, filed Jan. 22, 2013, entitled SYSTEM AND METHOD FOR DESIGNING WAVEFRONT-GUIDED OPHTHALMIC LENSES, which claims the benefit of U.S. Provisional Patent Application No. 61/588,956, filed Jan. 20, 2012, each of the foregoing applications being incorporated by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention is directed to vision care and more particularly to higher-order aberration correcting/inducing ophthalmic lenses to improve visual performance. 
       DESCRIPTION OF RELATED ART 
       [0003]    It has been well known that the human eye suffers from the optical defects called “wavefront aberrations,” which include both lower (defocus and astigmatism) and higher order aberrations (those of higher order than defocus and astigmatism). Optical and psychophysical tests have demonstrated that correcting those aberrations significantly improves visual performance, especially when the pupil size is relatively large. The visual benefit is even more substantial when correcting the aberration in eyes with abnormal corneal conditions such as keratoconus and penetrating keratoplasty. 
         [0004]    Adaptive optics is a powerful and noninvasive tool to achieve higher order correction. However, it is an impractical method. Although refractive surgery has been proven to be practical and effective to correct the aberration, it is a non-reversible surgical method, and its availability is restricted by factors such as corneal thickness and the amount of the aberration. 
         [0005]    Vision correction using practical, noninvasive customized (or wavefront-guided) ophthalmic lenses to correct the aberration has been increasingly important. Those special optical components include phase plates (spectacles), soft and hard contact lenses, and intraocular lenses (IOLs). However, such vision correction still has its limits. 
       SUMMARY OF THE INVENTION 
       [0006]    The invention is based on the inventor&#39;s realization that successful correction with those types of ophthalmic lenses requires ( 1 ) accurate measurement of the ocular aberration and ( 2 ) incorporating decentration and rotation of the lens with respect to the eye&#39;s pupil into the lens design. The measured aberration can include higher order aberration (that is, other than defocus and astigmatism, although they can include fifth- and higher order Zernike modes and even tenth-order Zernike modes). The invention implements a method for combining the measured aberration with decentration and rotation of the lens to design customized optical surface profiles to reliably achieve vision correction. Aspects of the invention are the method to measure the ocular aberration of the eye with the best fit conventional lens and to quantify the position and rotational orientation of the lens and techniques to effectively incorporate those measured values into the final two-dimensional lens surface profile. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    A preferred embodiment of the invention will be set forth in detail with reference to the drawings, in which: 
           [0008]      FIGS. 1A-1C  are diagrams showing the concept of customized soft contact lenses; 
           [0009]      FIG. 2  is a flow chart showing the design of customized soft contact lenses according to the preferred embodiment; 
           [0010]      FIG. 3  is an annotated photograph showing the determination of lens decentration and rotation; 
           [0011]      FIGS. 4A-4D  are diagrams showing the combination of lens movement and wavefront aberration when a lathing machine can fabricate only centered surfaces; and 
           [0012]      FIG. 5  is an annotated photograph showing the combination of lens movement and wavefront aberration when a lathing machine can fabricate decentered surfaces. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0013]    A preferred embodiment of the present invention will be set forth in detail with reference to the drawings, in which like reference numerals refer to like elements or steps throughout. 
         [0014]      FIGS. 1A-1C  illustrate the concept of customized ophthalmic lenses. As shown in  FIG. 1A , a conventional lens  102  applied to the patient&#39;s eye E provides only a spectacle prescription, leaving the irregular higher-order aberrations uncorrected. That leads to a blurred image  104  on the retina R, especially for larger pupils and eyes with corneal abnormalities such as keratoconus and corneal transplants. As shown in  FIG. 1B , a front-surface-customized ophthalmic lens  106  with an asymmetric surface profile  108  on the front side of the lens  106  corrects those higher-order aberrations to provide a sharp image  110 . 
         [0015]    In eyes with abnormal corneas, lens movements impair the correction performance, since the optical axis of the corrective lens is not aligned with the eye&#39;s optical axis. In order to reduce those lens movements, a back-surface-customized ophthalmic lens  112  can be implemented, as shown in  FIG. 1C . Such lenses conform to the cornea C better, since they are designed with irregular back surface profiles  114  cut according to the patient&#39;s anterior cornea. 
         [0016]      FIG. 2  illustrates the step-wise procedure for designing customized ophthalmic lenses. First, in step  202 , the anterior corneal topography of the subject is measured. The back surface of a conventional lens is cut according to those measurements in step  204 , leading to the aforementioned back-surface-customized contact lens. That step is not necessary if the front-surface-only customization provides satisfactory outcomes and may also be eliminated for any practical issues such as time and cost. The front-surface-customized lens is designed next, either as an addition over the back surface lens or as a standalone correction. The eye&#39;s wave aberration is measured in step  206  either with a conventional lens or with the back surface lens. Techniques for measuring wave aberrations are known in the art and are disclosed, e.g., in U.S. Pat. No. 5,777,719. Images of the eye are also recorded simultaneously to aid in calculating the lens movements to determine the decentration and rotation of the contact lens in step  208 . The corrective lens is designed by combining the lens movement and the wave aberration measurement in step  210  by one of two methods: a centered or decentered surface design method. The designed profile can further be optimized by modifying the designed surface in step  212 . Each higher-order aberration has a different impact on retinal image quality, and the higher the aberration order, the greater the sensitivity to the lens movements. Optimal selection of higher-order aberrations for which correction is attempted can be determined so that visual benefit can be maximized by minimizing the effects of the lens movements. From the measured movements of the lens over a period of time, a theoretical visual benefit can be evaluated by calculating improvement in image quality, e.g., the modulation transfer function with a different selection of aberrations to be corrected. The front surface of the lens is cut in step  214  according the final design obtained in the previous step. 
         [0017]      FIG. 3  shows the process of determining lens decentration and rotation. A conventional lens  302  with black marks  304  is worn by the subject. Using a camera and an existing automated computer algorithm, the center P of the pupil is estimated. Next, the center  306  of the lens  302  is estimated by calculating the center of the circle formed by joining the black marks. The vector displacement between the lens and pupil centers gives the horizontal (Δx) and vertical (Δy) decentration. Polar coordinates could be used instead. Rotation (Δφ) is obtained by calculating the orientation of a reference feature  308  from the vertical meridian (or any other previously determined default orientation). 
         [0018]      FIGS. 4A-4D  show the process of lens design when the manufacturing process allows fabricating only centered optical surfaces. Rotational orientation is taken into account separately. The measured wave aberration of the eye is first extrapolated, as shown in  FIG. 4A , to encompass the lens movement. However, extrapolation gives rise to increased and erroneous wavefront height at the edges of the optical zone. That leads to abrupt transition at the edge of the optical zone and increased lens material removal, thus leading to manufacturing errors. 
         [0019]    To overcome that problem, as shown in  FIG. 4B , the extrapolated wavefront is then weighted with a function to smooth the transition between the optical zone and lens edge. That function is described by a flat top with unity amplitude in the center across the eye&#39;s pupil with a Gaussian or exponential decay at the edges. That same smoothing function will also be used in the decentered surface design method described below. The resultant wavefront overcomes the previously mentioned limitation related to extrapolation. That wavefront is then remapped around the center of the lens by accounting for the lens decentration, as shown in  FIG. 4C . It is then fit to Zernike polynomials and serves as the final design of the ophthalmic lens in addition to its rotational orientation. During manufacturing, as shown in  FIG. 4D , the ophthalmic lens is rotated optimally to account for the static rotation of the lens on the eye. That design algorithm provides a benefit that rotational orientation becomes an independent design parameter, unlike the decentered surface design method. The lens can be manufactured in any suitable manner. Two examples are the use of a variform lathe  404  and laser ablation using a pulsed laser  406  and a scanning mirror  408 . The manufacturing process can be performed under control of a computer  410  that has been programmed to perform the operations disclosed in the present disclosure. 
         [0020]      FIG. 5  shows the process of lens design when the manufacturing process allows fabricating decentered optical surfaces. Horizontal (Δx) and vertical (Δy) lens decentration and lens rotation (Δφ) are estimated in the same manner as described above. Rotational orientation is taken into account separately and is also part of coordinate transformation. A coordinate transformation to incorporate lens decentration in the presence of rotation is performed to find the new lens center (x′, y′). The manufacturing process then modifies the surface profile of the lens with the new lens center as reference. During manufacturing, the lens is similarly rotated optimally to account for the static rotation. That method is a more direct and perhaps more reliable way of designing a customized surface, as it does not require the extrapolation process described above. 
         [0021]    Variations of the preferred embodiment can include:
       Back surface customization on the basis of corneal irregularity to stabilize lens movement;   Customized ophthalmic lenses by combining front and back surface customization;   Simultaneous recording of pupil images and eye&#39; s wave aberration to account for the effect of lens movement on optical correction;   Measurement of lens decentration and rotation;
           a. Lens marks to find lens center and pupil edge detection to find pupil center;   b. Estimation of decentration by calculating vector displacement between pupil and lens center;   c. Estimation of rotation by calculating orientation of a reference feature;   
           Combining lens movement and eye&#39;s wave aberration;
           a. Extrapolation and a weighting function to encompass lens decentration;   b. Remapping of the wavefront around the center of the lens to account for lens decentration;   c. Rotation of the ophthalmic lens before manufacturing to account for static rotation on eye;   d. Transforming the coordinate system to account for the lens decentration in the presence of lens rotation;   
           Optimizing outcome benefits on the basis of the measured lens movement statistics; and   Any suitable combination of the above.       
 
         [0036]    While a preferred embodiment of the present invention has been disclosed above, those skilled in the art who have reviewed the present disclosure will readily appreciate that other embodiments can be realized within the scope of the invention. For example, the data collection, computation, and fabrication can take place at the same location or remote locations. Therefore, the invention should be construed as limited only by the appended claims.