US20040130677A1 - Apparatus and method for measuring vision defects of a human eye - Google Patents

Abstract

An apparatus for measuring vision characteristics of an eye includes a laser for providing an optical beam and a focusing element for focusing the optical beam behind a retina of the eye for providing a finite source of secondary radiation on the retina of the eye. The secondary radiation is emitted from the retina as a reflected wavefront of radiation that passes outward from the eye. A polarizer is placed within a path of the optical beam for transmitting a polarized wavefront therethrough. A wavefront analyzer receives the polarized wavefront for measuring distortions associated therewith.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
• This application is a divisional of application Ser. No. 09/919,374, filed Jul. 31, 2001, now U.S. Pat. No. 6,598,975, which itself is a continuation-in-part of application Ser. No. 09/665,748, filed Sep. 20, 2000, now U.S. Pat. No. 6,270,221, which is a continuation of application Ser. No. 09/274,672, filed Mar. 24, 1999, now abandoned, which claimed priority to Provisional Application having Ser. No. 60/097,086, filed on Aug. 19, 1998 for “Apparatus and Method for Measuring Vision Defects of a Human Eye,” commonly owned with the instant application.[0001]
BACKGROUND OF INVENTION
• 1. Field of Invention[0002]
• The invention relates generally to optical aberration measurement and correction, and in particular to projection techniques in the objective measurement and correction of the human eye using a wavefront sensor.[0003]
• 2. Description of Background Art[0004]
• There has been and continues to be a need to provide a person with improved visual acuity. Remodeling of the cornea using refractive laser surgery or intracorneal implants, adding synthetic lenses using intraocular lens implants or precision ground contact lenses or eye glasses provide known solutions. Further, it is known to correct vision astigmatically by surgical modification of myopic or hyperopic astigmatism through laser keratoplasty, keratomileusis, or photorefractive keratectomy. Laser sources are used to erode or ablate surfaces of the eye, typically reshaping the cornea. Prior to and during such surgery, precise measurements must be made to determine required surgical corrections.[0005]
• The imprecise measurement technique of placing lenses of known refractive power anterior to the cornea and asking a patient which lens or lens combination provides the clearest vision has been improved with the use of autorefractometers, as described in U.S. Pat. No. 5,258,791 to Penny et al., or with the use of wavefront sensors as described by Liang et al. in “Objective Measurement of Wave Aberrations of the Human Eye with the Use of a Hartmann-Shack Wave-Front Sensor,” Journal of the Optical Society of America, Vol. 1, No. 7, July 1994, pp. 1949-1957, by way of example. Penny '791 discloses the use of autorefractometer measurements for determining the appropriate corneal surface reshaping to provide emmetropia, a condition of a normal eye when parallel rays are focused exactly on the retina and vision is optimum. Spatially resolved refraction data, in combination with measured existing surface contour of the anterior surface of the eye, enable a calculation of a detailed spatially resolved new contour that provides corrected vision.[0006]
• It would be an improvement in the art if such vision correction could be made without the need for these contour data, and further without the need for feedback from the patient regarding an appropriate lens. Liang et al. disclose the use of a Hartmann-Shack wavefront sensor to measure ocular aberrations by measuring the wavefront emerging from the eye by retinal reflection of a focused laser light spot on the retina's fovea. A parallel beam of laser light passes through beam splitters and a lens pair that brings the beam to a focus point on the retina by the optics of the eye. Possible myopia or hyperopia of the tested eye is corrected by movement of a lens within the lens pair. The focused light on the fovea is then assumed to be diffusely reflected and acts as a point source located on the retina. The reflected light passes through the eye and forms a distorted wavefront in front of the eye that results from the ocular aberrations. The aberrated wavefront is then directed to the wavefront sensor.[0007]
• A point source of radiation on the retina would be ideal for such measurements. However, when the perfect eye receives a collimated beam of light, the best possible image on the retina is a diffraction-limited spot. As illustrated by way of example, with Penny et al. and Liang et al., discussed above, and typical for those of skill in the art, collimated parallel beams are used with the optics of the eye being measured to achieve this diffraction-limited spot for such objective measurements. To do so requires that a setup for each patient include a corrective lens or lens combination and adjustments thereto for accommodating that patient's specific visual acuity. Providing a corrective or lens combination, as well as setting up for its use, becomes cumbersome and time consuming, and requires additional expense. Eliminating the need for such corrective optics is desirable and eliminates a variable within optical measurement systems that typically include many variables. Further, there is a need for providing optical characteristics of an eye without requiring feedback from the patient. By way of example, the patient may be a wild or domestic animal, living or dead.[0008]
SUMMARY OF INVENTION
• In view of the foregoing background, it is therefore an object of the present invention to provide a refraction measurement system that easily accommodates the measurement of vision characteristics of the eye, even in the presence of finite refractive errors.[0009]
• It is another object to improve upon the time required for a patient to be in a fixed position during examination, while at the same time providing a useful source of light on the retina of the eye to be measured regardless of the characteristics of the eye of that patient or other patients to be examined.[0010]
• It is a further object to measure such characteristics without requiring patient or operator feedback.[0011]
• These and other objects, advantages and features of the present invention, are provided by a method aspect of the invention for measuring optical characteristics of an optical system including the focusing of an optical beam proximate an anterior surface of the optical system, for placing a finite source of secondary radiation on a focal surface of the optical system, which secondary radiation is emitted from the focal surface as a reflected wavefront of radiation that passes through the optical system, transmitting the diffusely reflected wavefront onto a wavefront analyzer, and measuring characteristics of the optical system associated with the reflected wavefront.[0012]
• In a preferred embodiment, the method includes the step of measuring defects of the eye, which includes the steps of focusing an optical beam onto an anterior surface of the eye, other than the retina, for providing a finite source of secondary radiation on the retina of the eye, which secondary source of radiation is emitted from the retina as a reflected wavefront of radiation that passes through the eye, directing the reflected wavefront onto a wavefront analyzer, and measuring distortions associated with the reflected wavefront. A preferred embodiment of the invention includes the step of focusing the projected optical beam on the anterior surface of the cornea. In an alternate embodiment the optical beam is focused behind the retina.[0013]
• An apparatus for effectively performing such measurements includes means for focusing an optical beam onto an anterior surface of the optical system or eye, other than the retina, for providing a finite secondary source of radiation source on the focal surface, or retina of the eye, which finite secondary radiation source is emitted from the retina as a reflected wavefront of radiation that passes through the eye, means for directing the reflected wavefront onto a wavefront analyzer, and a wavefront analyzer for measuring distortions associated with the reflected wavefront. In one preferred embodiment of the present invention, a laser beam is focused onto the surface of the cornea with a long-focal-length lens, which converges the beam through a small angle for passing through the iris of the eye and providing a finite secondary source of radiation source on the retina of the eye, which finite secondary radiation source is emitted from the retina through the optics of the eye as the wavefront to be measured. In an alternate embodiment the apparatus comprises means for focusing the optical beam behind the retina[0014]
BRIEF DESCRIPTION OF DRAWINGS
• A preferred embodiment of the invention as well as alternate embodiments are described by way of example with reference to the accompanying drawings.[0015]
• FIG. 1 is a diagrammatic illustration of an apparatus for measuring visual defects of an eye, according to the present invention.[0016]
• FIG. 2 is a diagrammatic illustration of an eye being measured by the apparatus of the present invention, with the focus on the cornea.[0017]
• FIG. 2A is a diagrammatic illustration of an eye being measured by the apparatus of the present invention, with the focus behind the retina.[0018]
• FIGS. 3A and 3B are diagrammatic illustrations of an ideal eye with perfect vision and an aberrated eye, respectively.[0019]
• FIG. 4 is a diagrammatic illustration of an eye being measured with collimated light focused on the retina to a diffraction-limited spot.[0020]
• FIG. 5 is a partial perspective view of a pinhole imaging plate and detector plane of a wavefront sensor used in a preferred embodiment of the present invention.[0021]
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
• The present invention will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout.[0022]
• A preferred embodiment of a[0023]measurement apparatus10 of the present invention is herein initially described with reference to the schematic diagram of FIG.1. Abeam12 of optical radiation is directed into aneye14 to be measured, so that a small area orspot16 is formed as a secondary source of radiation in the foveal region of the retina18 (FIG. 2). Specifically, thebeam12 is focused through asmall angle13 onto ananterior surface20 of theeye14, other than the retina, and in a preferred embodiment of the present invention, focused on an anteriorcorneal surface22 of thecornea24 for further projection through theiris26 andlens28 and onto theretina18.
• In an alternate embodiment of the invention, a projected[0024]beam12′ of optical radiation is directed into aneye14′ to be measured, so that a small area ormeasurable spot16′ is formed as a secondary radiation source in the foveal region of theretina18′ (FIG. 2A). Specifically, thebeam12′ is focused through asmall angle13′ at a point behind theeye14′, after passing through theiris26′, thelens28′, and theretina18′.
• By way of further background, consider an “ideal”[0025]eye14iwith ideal vision, as illustrated with reference to FIG. 3A. Theideal eye14i,having theideal cornea24iandideal lens28i,will focus a collimated beam of light, illustrated witharrows30 to apoint32, as the secondary radiation source, on theideal retina18i.Thispoint32 would then be a point source of light that would be diffusely reflected back through the optics of theideal eye14ias a sequence of plane waves34. In actual fact, even an eye having perfect vision, as illustrated by way of example with reference to FIG. 4, will produce a diffraction-limited illuminated area orspot36 as the secondary radiation source on the retina of the eye, under the best possible circumstances. In a typical eye, as illustrated with reference to FIG. 4, such aspot36 is even larger, where most of the blurring will be due to finite aberrations found in typical eyes. By way of further example, in anaberrated eye14a,from thepoint source32 distortedwavefronts38 result, as illustrated with reference to FIG. 3B. Having to deal with a series of distortedwavefronts38 resulting from aberrations, and further dealing with a blurring of suchdistorted wavefronts38 resulting from diffraction effects and the finite aberrations of the eye, results in aspot36 source of light rather than apoint32 source, representing one of the challenges in measuring the visual defects or an eye.
• It is typical in the art of eye measurement to form a collimated beam and attempt to focus the collimated beam onto the retina, using lenses and lens combinations with the optics of the eye to produce the smallest[0026]possible spot36, as earlier described with reference to FIG. 4. Using lenses and focusing techniques typically takes valuable time and includes multiple attempts to focus a spot on the retina with the use of various lenses and lens combinations to accommodate the unique vision of each patient being measured. With the present invention, and the understanding that most of the blurring results from the curvature of the cornea, the present invention eliminates the need to find lenses or lens combinations to minimize the size of the spot on the retina that is used as the secondary source of radiation.
• With reference again to the embodiment described in FIGS. 1 and 2, the[0027]optical wavefronts40 scattered from theretina18 are transferred by a series of optical elements, which will be described in further detail in the following, to awavefront sensor42, which divides each incident wavefront into a group of “wavelets,” referred to herein withnumeral50, using anopaque plate44 having a planar array of apertures46 (FIG. 5). Further, thewavefront sensor42 records theposition48 at which eachwavelet50 passing through theaperture46 strikes adetector plane54 such as a charged-coupled device (CCD), herein provided as one preferred embodiment, the plane being held a fixedsmall distance56 behind theplate44. Thetransverse displacement58 of eachwavelet50 at theCCD detector plane54 from a collimatedlight reference position60 is then used to calculate a wavefront slope at each position of theapertures46 within the planar aperture array. Alternate methods exist for using partial derivative data resulting from the measurements of the slope to calculate thewavefront40. One acceptable approach is that used by Liang et al. in the aforementioned paper, where the wavefront is closely approximated using Zernike polynomials.
• At each[0028]position48, aspot62 typically extending beyond the light measurement area of oneCCD element64 is produced. As earlier discussed, blurring and a large diffraction-limited spot make it difficult to make measurements. Thus reducing blurring improves measurement at thedetector plane54.
• With reference again to FIG. 1, in one preferred embodiment of the present invention, the[0029]apparatus10 includes the projectedbeam12 of linearly polarized light (S-component) emitted from a diode laser66 (670 nm, 3 mW, by way of example). The beam of light passes through anelectromechanical shutter68, which controls the duration of light exposure on theeye14 of the patient. The exposure of theretina18 of theeye14 illustrated with reference again to FIG. 2. It is expected that alternate sources of light, for example, noncoherent and nonpolarized as well as alternate light-transmitting techniques, will be recognized by those skilled in the art without deviating from the teachings of the present invention. As herein described, the use of coherent light from a laser and polarization techniques are currently preferred.
• When the[0030]shutter68 is open, the projectedbeam12, collimated light from thediode laser66, is directed by a longfocal length lens70 for focusing on theanterior surface22 of thecornea24 of the eye14 (FIG. 2), passing through thepupil72 andlens28 of theeye14, and onto theretina18 as thesmall spot16. In an alternate embodiment,lens70 comprises a zoom lens for varying the focus and moving the focus location as desired. By focusing on thecornea24, the measurement is minimally dependent on the curvature of the cornea. However, other locations proximate the corneal surface are acceptable.
• While diffraction and various aberrations are present, the present invention avoids the aberration effects from the cornea, which typically dominate. The[0031]lens28 of theeye14 contributes a relatively small aberration effect when compared with that of thecornea24. Further, and with regard to the selection oflens70, selecting a lens with a short focal length would provide alarge angle13, a well-focusedpoint78 on the surface of thecornea24, and fewer aberration effects from the cornea. However, alarge angle13 results in an undesirably largerretinal spot16. Thesmall angle13 herein described provides alarger focus point78 on thecornea24 but the more desirablesmaller spot16 on theretina18. Thespot16 will depend on the wavelength, starting point size, and focal length of thelens70 selected. In preferred embodiments of the present invention, lenses of approximate one-half meter are selected for thelens70. A 100-mm lens70 has also been effectively used.
• In one preferred embodiment herein described, a[0032]mirror74 andpolarization beamsplitter76 direct thebeam12 to afocus78 on theanterior surface20 of thecornea24. Thebeam12, focused on theanterior surface22 of thecornea24, provides thespot16 as a light source (about 1.5 milliradians in visual space, by way of example) on theretina18 of theeye14 being measured (FIG. 2). Such aspot16 provides an acceptable substitute for a diffraction limited spot typically sought. By way of one preferred example of use, a method for measuring vision characteristics of theeye14 includes directing thebeam12 through the long-focal-length lens70 for providing the small angle13 (FIG. 2), about an optical path for passing thebeam12 through thepupil72 of theeye14. Thebeam12 is first focused at a fixedlocation78, without the eye or patient in place. All measuring equipment, theapparatus10, is arranged without the patient in place and at a convenient time prior to measuring. Then the patient is positioned such that the anterior surface of theeye14 of a patient is located at the fixedlocation78, which in a preferred embodiment is the anterior surface of the cornea. This forms a finite source of secondary radiation, thespot16, as herein described, on theretina18 of theeye14, which provides light emitted from theretina18 and through thepupil72 as a reflected wavefront, the wavefront38 (FIG. 3B). Thiswavefront38 is directed onto thewavefront analyzer42 for measurement.
• In a preferred embodiment, the laser power reaching the eye is physically limited to a maximum of 7 μW. In measurements on a human eye using the[0033]apparatus10, a laser pulse duration of 700 ms was used so that the total energy entering the eye would not exceed 4.9 μJ. For comparison, according to the ANSI standard for direct “intrabeam” viewing, the maximum permissible exposure to a laser at the wavelength used is 530 μJ. Thus the probing laser energies effectively used in the present invention are two orders of magnitude below an “eye-safe” limit.
• With reference again to FIG. 1, the light emitted by secondary source of[0034]radiation16 produces thewavefront40, a distorted wavefront at the pupil plane due to the eye's aberrations. Diffuse reflection makes the returning light from the retina depolarized, containing not only an S-component but also a P-component polarized light. Thepolarization beamsplitter76 in front of theeye14 will only let the P-component pass through it and downstream of thewavefront sensor42. The S-component is essentially totally reflected toward thediode laser66. Because the light reflected by corneal surface preserves the polarization of the incoming beam (S-polarized), the corneal reflection is reflected by thebeamsplitter76 and is thus rejected from thepath80 heading toward thewavefront sensor42. The P-component of theaberrated wavefront40 at the subject's pupil plane is then re-created by the combination oflens82 andlens84, at a trial lens plane86 (FIG. 1). In one preferred embodiment, the diameter and the effective focal length of the two substantiallyidentical lenses82 and84 are 40 and 120 mm, respectively. The combination oflenses82 and84 forms an afocal image system with the eye's pupil72 (the object plane) at the focal plane of thelens82, and the image plane,trial lens86, at the focal plane of thelens84. Similarly,lenses88 and90 also form an afocal image system with thepossible trial lens86 at the front focal plane of thelens88 and the lens combination at the image plane at the back focal plane of thelens90. The focal plane of thelens90 is located at theplate44 of thewavefront sensor42, earlier described with reference to FIG. 5. In a preferred embodiment,lens88 has an effective focal length of 80 mm.Lens90 has an effective focal length of 120 mm. With theapparatus10, measured wavefront slopes leaving theeye14 are re-created at theaperture plane44 and magnified by a factor of 1.5. Magnification of the diameter of thewavefront40 at thedetector plane54 reduces the wavefront slopes by the same degree. This extends the dynamic range of eye aberrations over which the device can measure.
• By way of further explanation about the trial lens location or[0035]plane86, because thewavefront40 leaving theeye14 is re-created at thislocation86 with unity magnification, a trial lens of known refractive power inserted at this point should exactly compensate for a prescribed refractive error. For example, a perfect five-diopter lens placed at this location should remove five diopters of spherical curvature from an incident wavefront, without altering other aberrations that may exist in the wavefront. The capability of inserting trial lenses at thislocation86 extends the dynamic measurement range of theapparatus10, without affecting wavefront analyzing capability.
• In a preferred embodiment, and with reference again to FIG. 5, the[0036]aperture array46 of thewavefront sensor42 samples theincident wavefront40, which forms focusspots62 on thedetector plane54. This is repeated at thedetector plane54 for each aperture within thearray46. As a result, a localized direction of thewavefront40 is determined for each of a plurality ofwavelets50 within the array. By way of example, the use of lenslets92 (as an alternate embodiment ofapertures46 alone), with a focal length of 87 mm and a dimension of 0.768 mm, forms an aerial image of the retinal light source (thespot16 described earlier with reference to FIG. 2) on thedetector plane54. If a plane wave, corresponding to an aberration-free eye, were measured, thelenslet92 array would produce a regular array of focused spots on the image sensor. When thereal eye14 is measured, the wave aberration in the eye will displace the focus spot62 (FIG. 5), of each lenslet92 from thereference position60 to the measuredposition50 in proportion to the local slopes of thewavefront40. Thewavefront sensor42 measures the local wavefront slopes at an array of sampling locations across thepupil72, from which thewavefront40 itself can be reconstructed.
• As illustrated again with reference to FIG. 1, in an alternate embodiment of the present inventive methods, a[0037]fixation target94 may be used to ensure that the patient is looking along the optical axis of theapparatus10. The patient is asked to fixate on thetarget94 located at the focal plane of alens96. By linearly moving theoptics combination96 of thefixation target94, it is possible to provide the eye's spherical correction, and hence to make thefixation target94 clearly visible to the subject. In one preferred use, the image of thefixation target94 is intentionally undercorrected for each patient to ensure that the measuredeye14 is focused at infinity. By way of example, the fixation target consists of a dark cross-hair and a number of concentric circles on a white background that is back-illuminated by a tungsten lamp. The patient is asked to look at the center of the cross-hair. The position of theeye14 in reference to the optical axis is recorded byCCD camera98. ThisCCD camera98 is conjugate, in effect coupled, to the eye'spupil72 through asecond lens combination100, preferably mounted on the camera, and thelenses82,84. In one method of te present invention, thecamera98 is used to view theeye14 for aligning the eye within the path ofte beam12 for assuring that the beam passes through thepupil72. Thecamera98 is also useful in an alternate embodiment of the present invention, for viewing the size of thespot16 formed on theretina18 as the user changes thefocus point78 through various anterior surface locations in obtaining an optimum size of thespot16.
• By way of further example of effective uses of the present invention, the earlier described Zernike coefficients of an eye, taken collectively, can be used as discriminating as fingerprints or DNA. The Zernike coefficients for a person might be used for identification of that person for permitting access to a confidential area, allowing funds to be distributed through an ATM, and the like. Further, the present invention allows eye measurements for a passive subject, such as in the examination of a corpse or sedated animal. The present invention is operable with human eyes, as herein described, as well as those of an animal, bird, or fish eyes, and in particular, nonbiological focusing optical systems such as those found in cameras. The present invention is useful in developing optimized aspheric systems, where an aspheric element need to be designed last by observing and producing a single custom aspheric element that corrects the system. By way of example, the aspheric system may be designed on paper except for the correcting element, which would be developed experimentally using the present invention as herein described. The design of afocal systems such as a telescope, a searchlight, or a projector which require an added corrective focus element will benefit from the present invention.[0038]
• Many modifications and other embodiments of the invention will come to the mind of one skilled in the art having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed, and that modifications and alternate embodiments are intended to be included within the scope of the appended claims.[0039]

Claims (22)

That which I claimed I:

1. An apparatus for measuring vision characteristics of an optical system, the apparatus comprising:

focusing means for focusing an optical beam proximate a posterior surface of the optical system for providing a finite source of secondary radiation on a focal surface, the posterior surface other than the focal surface, which secondary radiation is emitted from the focal surface as a reflected wavefront of radiation that passes through the optical system;

directing means for directing the reflected wavefront onto a wavefront analyzer; and

a wavefront analyzer for measuring distortions associated with the reflected wavefront.

2. The apparatus recited inclaim 1, wherein the focusing means comprises a long-focal-length lens for converging the optical beam through a small angle and focusing the optical beam on the anterior surface.

3. The apparatus recited inclaim 2, wherein the long-focal-length lens has a focal length of at least one-half meter.

4. The apparatus recited inclaim 1, wherein the focusing means comprises a zoom lens for converging the optical beam through a small angle and varying the focusing of the optical beam onto various anterior surfaces.

5. The apparatus recited inclaim 1, further comprising a laser for providing the optical beam.

6. The apparatus recited inclaim 1, further comprising the a shutter operable from a closed position to an open position for controlling an amount of optical beam energy delivered to the optical system.

7. The apparatus recited inclaim 1, wherein the wavefront analyzer comprises:

an opaque plate having an aperture therein for transmitting a portion of the emitted wavefront therethrough; and

a light-sensitive material downstream of and in spaced relation to the opaque plate for receiving the portion of the reflected wavefront projected as a finite image thereon.

8. The apparatus recited inclaim 7, wherein the aperture comprises an aperture array and wherein the light-sensitive material comprises a CCD array.

9. The apparatus recited inclaim 8, further comprising a lens carried within each of the plurality of apertures of the aperture array.

10. The apparatus recited inclaim 1, further comprising polarizing means for polarizing the optical beam.

11. The apparatus recited inclaim 10, further comprising a polarization beamsplitter for reflecting an S-component of the reflected wavefront and for transmitting a P-component of the reflected wavefront as a polarized wavefront therethrough.

12. The apparatus recited inclaim 1, further comprising a camera positioned for viewing the focal surface.

13. An apparatus for measuring vision characteristics of an eye, the apparatus comprising:

a laser for providing an optical beam;

focusing means for focusing the optical beam behind a retina of the eye for providing a finite source of secondary radiation on the retina of the eye, which secondary radiation is emitted from the retina as a reflected wavefront of radiation that passes outward from the eye;

polarizing means placed within a path of the optical beam for transmitting a polarized wavefront therethrough; and

a wavefront analyzer receiving the polarized wavefront for measuring distortions associated therewith.

14. The apparatus recited inclaim 13, wherein the focusing means comprises a long-focal-length lens for converging the optical beam through a small angle and focusing the optical beam on the anterior surface.

15. The apparatus recited inclaim 14, wherein the long-focal-length lens has a15 focal length of approximately one-half meter.

16. The apparatus recited inclaim 13, further comprising the a shutter operable from a closed position to an open position for controlling an amount of optical beam energy delivered to the eye.

17. The apparatus recited inclaim 13, wherein the wavefront analyzer comprises:

an opaque plate having an aperture therein for transmitting a portion of the emitted wavefront therethrough; and

a light-sensitive material downstream of and in spaced relation to the opaque plate for receiving the portion of the reflected wavefront projected as a finite image thereon.

18. The apparatus recited inclaim 17, wherein the aperture comprises an aperture array and wherein the light-sensitive material comprises a CCD array.

19. The apparatus recited inclaim 18, further comprising a lens carried within each aperture of the aperture array.

20. The apparatus recited inclaim 13, further comprising a fixation target for viewing by a patient whose eye is being measured, the fixation target assuring that a patient whose eye is being measured is looking along a preferred direction.

21. The apparatus recited inclaim 13, further comprising a camera positioned for viewing the focal surface.

22. A method for measuring vision defects of an eye comprising the steps of:

focusing an optical beam anterior of the retina of the eye, but not on the retina, for placing a finite source of secondary radiation on the retina, which secondary radiation is emitted from the retina as a reflected wavefront of radiation that passes through the eye;

projecting the reflected wavefront onto a wavefront analyzer; and

measuring distortions associated with the reflected wavefront.

Images