Classifications

• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B3/00—Apparatus for testing the eyes; Instruments for examining the eyes
  • A61B3/10—Objective types, i.e. instruments for examining the eyes independent of the patients' perceptions or reactions
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B3/00—Apparatus for testing the eyes; Instruments for examining the eyes
  • A61B3/10—Objective types, i.e. instruments for examining the eyes independent of the patients' perceptions or reactions
  • A61B3/14—Arrangements specially adapted for eye photography
  • A61B3/15—Arrangements specially adapted for eye photography with means for aligning, spacing or blocking spurious reflection ; with means for relaxing
  • A61B3/156—Arrangements specially adapted for eye photography with means for aligning, spacing or blocking spurious reflection ; with means for relaxing for blocking
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J9/00—Measuring optical phase difference; Determining degree of coherence; Measuring optical wavelength

Definitions

• the present invention is directed to a wavefront sensor, such as a sensor for wavefront aberrations in the eye, and more particularly to such a sensor which avoids conical reflection by illuminating the retina along a light path off of the optical axis of the eye.
• the present invention is further directed to a method of sensing a wavefront using such off-axis illumination.
• the emergent beam is applied to a Hartmann-Shack detector to detect the aberrations.
• a detector includes an array of lenslets which break up the light into an array of spots and focus the spots onto a charge-coupled detector or other two- dimensional light detector.
• Each spot is located to determine its displacement from the position which it would occupy in the absence of wavefront aberrations, and the displacements of the spots allow reconstruction of the wavefront and thus detection of the aberrations. Improvements to the technique of Liang et al are taught in J. Liang and D. R. Williams, "Aberrations and retinal image quality of the normal human eye,” .Journal of the Optical Society of America, Vol. 4, No. 1 1 , November, 1997, pp.
• the techniques described above involve illuminating the eye along the eye's optical axis. As a consequence, the light reflected from the retina is mixed with stray reflections which can disrupt measurements. More specifically, the stray reflections show up as spurious bright spots amid the array of spots formed in the Hartmann- Shack sensor.
• Such stray reflections have several sources in wavefront sensors. Of particular concern are the reflections from the optical elements between the retina and the beamsplitter. Such elements typically include the optics of the eye and a pair of lenses between the beamsplitter and the eye. Back reflections from surfaces other than the retina are weak relative to the illuminating beam but are bright relative to the weak signal reflected from the retina.
• the only surface whose back reflection is bright enough to be problematic is the first (outer) surface of the cornea. That reflection is comparable in energy to the reflection from the retina and can therefore be a considerable nuisance for wavefront sensing, particularly if the centroids of the spots in the detector are to be computed automatically.
• German published patent application No. DE 42 22 395 Al teaches that technique. That technique allows a much greater part of the light reflected from the retina to reach the detector, thereby improving spot quality, while removing the variation in spot brightness caused by the birefringence of the eye. It also removes back reflection from the lenses. However, the corneal reflection is not removed and is thus just as troublesome as it would be in the absence of polarizing optics.
• the present invention is directed to a wavefront sensor in which the eye is illuminated off-axis.
• the light not reflected by the cornea impinges on the retina, and the light reflected by the retina returns through the lens and the cornea. That light is thereby focused into an optical path different from the optical path followed by the corneal reflection.
• the entire retinal reflection is used, and the corneal reflection can be discarded by use of simple, inexpensive, non-polarizing optics such as a stop.
• the beam used to illuminate the eye is relatively narrow, e.g., around 1-1.5 mm in diameter, and intersects the cornea in a small area, thus further reducing the probability that the corneal reflection will take a return path to the detector.
• the dioptric range over which the small spot is in focus on the retina can be increased.
• a displacement of the illuminating beam from the optical axis of the eye by less than one millimeter completely removes the corneal reflection.
• the illuminating beam is preferably introduced into the optical path at the last possible location before the eye, e.g., by placing the beamsplitter right before the eye.
• the beamsplitter right before the eye.
• the light source can be moved in a direction perpendicular (or, more generally, non-parallel) to the direction of its output as needed to accommodate the eyes of different patients.
• the present invention has utility in any procedure involving wavefront sensing of the eye or otherwise involving illumination of the retina. Such procedures include, but are not limited to, autorefraction, design of contact or intraocular lenses, refractive surgery and retinal imaging with adaptive optics. While it is contemplated that the present invention will be used with the human eye, veterinary or even non-eye-related applications can be developed as well.
• Fig. 1 is a schematic diagram showing the basic optical concepts implemented in a preferred embodiment of the invention
• Figs. 2-4 are schematic diagrams showing an arrangement of optical elements in a wavefront sensor according to the preferred embodiment.
• Figs. 5 and 6 show experimental results obtained according to the preferred embodiment and the prior art, respectively.
• Fig. 1 shows an overview of a basic system 100 for illuminating the retina of the patient's eye E and will be used to explain the optical principles implemented in the preferred embodiment.
• a laser light source 102 such as a laser diode, emits a beam of light L, toward a beamsplitter 104, which can be a parallel-plate beamsplitter, a thick-plate beamsplitter, a prism beamsplitter, a half-silvered mirror, or another suitable beamsplitter.
• the beamsplitter 104 is preferably 90% trnasmissive and 10% reflective, although other ratios could be used as needed.
• the laser light source 102 and the beamsplitter 104 are positioned such that the light L, impinges on the eye E off of the optical axis A of the eye E.
• a light beam L 3 reflected from the retina R of the eye E exits the eye E and passes through the beamsplitter 104.
• the light beam L 3 then passes through a lens 106, a stop 108 which passes the light beam L 3 reflected from the retina while blocking the light beam
• Figs. 2-4 show a second-generation system 200 using the optical principles just explained with reference to Fig. 1.
• Fig. 2 shows a lower level 202 of the system 200 as seen from above, while Fig. 3 shows an upper level 204 of the system 200 as seen from above, and Fig. 4 shows both levels 202, 204 of the system 200 as seen from the right.
• Fig. 1 shows a lower level 202 of the system 200 as seen from above
• Fig. 3 shows an upper level 204 of the system 200 as seen from above
• Fig. 4 shows both levels 202, 204 of the system 200 as seen from the right.
• the lower level 202 as shown in Fig.
• a laser diode 206 is mounted on a mount 208 for horizontal positioning. The purpose of such positioning will be explained below.
• a light beam emitted from the diode 206 follows a lower-level light path designated generally as L, through lenses 210 and 212.
• the light beam is retroreflected by a comer mirror 214 and passes through a lens 216 to a mirror 218 which reflects the light beam upward.
• a parallel-plate beamsplitter 220 receives the light beam reflected upward by the min-or 218 and directs that light beam along an upper-level light path designated generally as L ( .
• the path L ⁇ is shown in greatly simplified form; the above discussion of Fig. 1 will provide those skilled in the art with an understanding of the requirements for the true optical path.
• the light beam illuminates the eye E in the manner explained above with reference to Fig. 1.
• a retinal reflection light beam reflected by the retina R of the eye E travels back through the beamsplitter 220 and a lens 222.
• the retinal reflection light beam is then retroreflected by a comer mirror 224 through a lens 226 to a Hartmann-Shack detector
• a stop can be included at an appropriate location along the light path L U5 e.g., at the focus of the lens 222.
• a single mirror can be used to replace the mirrors 214 and 224.
• the diameter of the incident light beam is a suitable value, e.g., 1.5 mm. The small diameter increases the depth of focus on the retina, thus relaxing the requirement to focus the light on the patient accurately.
• the small diameter also ensures that the spot on the retina will be diffraction- limited.
• the entry beam should be no smaller than approximately the diameter of a lenslet in the lenslet array. Otherwise, diffraction in the entering beam will significantly blur the spots on the CCD.
• the entry beam is displaced in the pupil from the corneal pole by a distance of more than one-half the diameter of the beam to separate the corneal and retinal reflections and thereby to avoid the effects of corneal reflection and is preferably displaced by about 1 mm.
• the distance may vary from subject to subject and can be less than 1 mm because of the small entrance beam diameter.
• the distance can be varied with the mount 208, which translates the diode 206 and its collimating optics by a small amount. The ability to translate the diode 206 and its optics by up to 1 mm suffices.
• the reflected light from the cornea is diverged and collimated by the lens
• Back reflections from other optical components can be avoided by placing the beamsplitter 220 in the last possible place, just before the eye E. That arrangement allows the illuminating beam to avoid the other optical elements, since the only thing between the beamsplitter 220 and the retina R is the cornea C.
• the usual reflections from the beamsplitter can be avoided by using a rotated beamsplitter cube or a thick-plate beamsplitter. It is not necessary to subtract an image without the eye in place from an image with the eye in place to remove stray light, as was often required in the prior art.
• the optical path length of the system 200 can be varied by coupling the mirrors 214 and 224 to a slide mechanism 234 so that the mirrors 214 and 224 can be moved as a single rigid body.
• the mirrors 214 and 224 are displaced from each other axially.
• the movement of the slide mechanism 234 by a distance x changes the optical path length of each level 202, 204 by a distance 2x and of the system 200 as a whole by a distance 4x.
• a slide mechanism allows the entering beam to be focused on the retina at the same time and with the same device with which the exit beam is focused on the CCD array, namely, the slide 234 bearing the mirrors 214 and
• the slide 234 Since the mirror 214 is in the path of the illuminating beam before that beam reaches the beamsplitter 220 and the mirror 224 is in the path of the exit beam, movement of the slide 234 changes the path lengths of both beams and thereby allows adjustment of the focus of both beams.
• the slide 234 thus provides economy and convenience.
• Double slide mechanisms could be implemented in the system 200.
• another mirror (not shown) could be placed opposite the mirrors 214 and 224 to cause the light beam to make another pass through the system.
• movement of the slide mechanism 234 by a distance x would change the total optical path length by a distance 8x.
• Figs. 5 and 6 show experimental results in Figs. 5 and 6.
• Fig. 5 shows a result taken with off-axis illumination according to the present invention, with no polarizing beamsplitter and with an SLD light source emitting a wavelength ⁇ - 790 mm.
• the spot pattern shown in Fig. 5 has much better intensity uniformity than that of Fig. 6 and has an average spot intensity four times higher than that of Fig. 6.
• the spot pattern of Fig. 5 is comparable to that obtained with a polarizing beamsplitter and a ⁇ /4 plate, without the drawbacks of that technique.
• the single non-polarizing beamsplitter 220 which can be a parallel plate beamsplitter or the like, is less expensive than the optics required for the polarizing techniques of the prior art, with or without a ⁇ /4 plate.
• the use of a beamsplitter with a ratio of transmittance to reflection greater than one further increases the light available.
• the present invention offers many advantages. The deleterious effects of back reflections in the eye and other optics are avoided, thereby making the instrument more robust and the software to operate it simpler. The quality of the spot images is not degraded by polarization effects, so that accuracy is improved. The throughput is higher than that of the prior art, so that a greater signal can be achieved for the same level of illumination and thus the same level of patient comfort and safety.
• the same signal as in the prior art can be achieved with reduced illuminating light intensity and thus improved patient comfort and safety.
• the ratio of transmission to reflection of the plate beamsplitter can be chosen to transmit almost all of the light from the retina to the CCD array. Since no polarizing optics are required, the cost is reduced.
• the optical path can have additional folds for improved path length and compactness, and a fixation target and pupil camera can be added.
• the light source can be positioned in any manner which spatially separates the retinal and corneal reflections, e.g., by selection of an appropriate angle of incidence. Therefore, the present invention should be construed as limited only by the appended claims.

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• 1999
  • 1999-10-21 US US09/422,338 patent/US6264328B1/en not_active Expired - Lifetime
• 2000
  • 2000-10-20 HK HK03100735.7A patent/HK1049435B/en not_active IP Right Cessation
  • 2000-10-20 CN CNB008145776A patent/CN1220466C/zh not_active Expired - Fee Related
  • 2000-10-20 JP JP2001531013A patent/JP4656791B2/ja not_active Expired - Fee Related
  • 2000-10-20 AU AU14354/01A patent/AU781573B2/en not_active Ceased
  • 2000-10-20 CA CA002388775A patent/CA2388775C/en not_active Expired - Fee Related
  • 2000-10-20 EP EP05008540A patent/EP1561416B1/en not_active Expired - Lifetime
  • 2000-10-20 EP EP00976606A patent/EP1235508B1/en not_active Expired - Lifetime
  • 2000-10-20 KR KR1020027004987A patent/KR100734515B1/ko not_active Expired - Fee Related
  • 2000-10-20 BR BRPI0014924-1A patent/BR0014924B1/pt not_active IP Right Cessation
  • 2000-10-20 ES ES05008540T patent/ES2277306T3/es not_active Expired - Lifetime
  • 2000-10-20 ES ES00976606T patent/ES2269198T3/es not_active Expired - Lifetime
  • 2000-10-20 ES ES05008541T patent/ES2279465T3/es not_active Expired - Lifetime
  • 2000-10-20 WO PCT/US2000/029008 patent/WO2001028411A1/en not_active Ceased
  • 2000-10-20 EP EP05008541A patent/EP1561417B1/en not_active Expired - Lifetime
  • 2000-10-20 DE DE60032528T patent/DE60032528T2/de not_active Expired - Lifetime
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