Patent Application
20070070292
This application relates to systems and methods for refractive vision corrections and refractive vision diagnosis.
Wavefront-guide vision correction is becoming a new frontier for vision and ophthalmology because it offers supernormal vision beyond conventional sphero-cylindrical correction, allows imaging of living photoreceptors, and perfects laser vision correction. Wavefront technology will reshape the eye care industry by enabling custom refractive corrections based on aberrations in individual eyes, reliable vision diagnosis and comprehensive specification of refractive vision corrections.
Wavefront technology is based primarily on precise measurements of eye's wave aberration using a device called wavefront sensors (aberrometers). One popular approach for the wavefront measurement is to measure the outgoing wavefront at the corneal plane using a Hartmann-Shack sensor as described in Liang et al. 94', “Objective measurement of wave aberrations of the human eye with the use of a Hartmann-Shack wave-front sensor,” J. Opt. Soc. Am. A, vol. 11, no. 7, p. 1949, July 1994.
The illumination probing light in
Different approaches were disclosed to address the issue of corneal reflection since the introduction of wavefront sensor. Liang et al 94' described a method of placing an aperture at the conjugate plane of the retina. Because the aperture is conjugate to the retina, it can reduce corneal reflection without affecting the wavefront from the retina. However, corneal reflection around the corneal vertex cannot be eliminated completely because it cannot be separated from the retinal reflection. Williams and Yoon in U.S. Pat. No. 6,264,328B1 described a so-called off-axis approach that uses an illumination beam positioned away from cornea vertex and an aperture placed at the conjugate point of the retina reflection to block the cornea reflex. Although the off-axis approach was described inexpensive, its actual implementation relies on expensive opto-mechanical systems for the correction of focus error in the eye. Without a proper correction for the eye's focus error, the aperture will not only block the corneal reflex, but also the retinal reflection. Additionally, requiring the correction of focus error in the eye before a wavefront measurement makes the wavefront measurement time-consuming if the sphero-cylindrical errors in an eye are not known in advance. A desired approach for blocking the corneal reflection should work indifferently for all eyes without a need for correcting any wavefront error in the eye. Liang and Williams described a method of removing corneal reflection using a polarization beamsplitter in “Aberrations and retinal image quality of the human eye,” J. Opt. Soc. Am. A, vol. 14, no. 11, p. 2873,1997. An illumination light through the polarization beamsplitter produces a linear polarized light as the probing beam into the eye. Because the corneal reflection preserves the polarization direction of the probing beam while the retinal reflection is depolarized, corneal reflection can be removed by the same polarized beamsplitter in the detection arm. The polarization approach is effective for a probing light with a relatively large beam size, but not so effective for illuminations with a beam size smaller than 1 mm, as shown in
Wavefront measurements using a Hartmann-Shack sensor require two measurements: one reference measurement from a known reference such as a perfect plane wave and one measurement from the tested object. Every focus spot in a wavefront image of a Hartmann-Shacks sensor has to be uniquely registered to its corresponding lenslets for at least two reasons. First, background errors in the wavefront system are recorded in the reference measurement and can be eliminated. Second, registration of wavefront map to the pupil of eye requires position information of the measured wavefront map in a fixed coordinate system. Unique registration of focus spots without a registration mark in the wavefront sensor was disclosed by using a fixed array of lenslets defined by an aperture in front of a lenslet array in Liang et al. 94'. Wavefront measurement using a fixed array of lenslet is however limited because natural pupil sizes for different eyes vary greatly. Because measuring aberrations in a full natural pupil is important for evaluating night vision, it is therefore apparent that a need exists in the art to provide a wavefront sensor in which each focus spots is uniquely registered to its corresponding lenslet. More particularly, the wavefront sensor must have an unrestricted lenslet array for testing eyes of any pupil size.
Wavefront sensors measure aberration of an eye objectively and the measured wavefront may contain an accommodation offset because tested eyes do not necessarily accommodate at its far accommodation point during a wavefront measurement. Wavefront fusion algorithms were disclosed in U.S. patent application Ser. No. 11/432,273, titled “Wavefront Fusion Algorithms for Refractive Vision Correction and Vision Diagnosis,” filed on May 10, 2006 by Liang to address the issue of accommodation offset. The fusion algorithms rely on data from two devices: a wavefront sensor for wave aberration and a phoroptor for a manifest refraction. A clinical setting using two separate systems is not preferred because it is expensive, time-consuming, and requires more office space. It will be apparent that a need exists in the art to provide a single wavefront-based system with which both the conventional manifest refraction and the high-order aberrations of the eye can be measured quickly and accurately in a cost-effective manner. More particularly, it is highly desired to have a single wavefront system to provide measurements of eye's wave aberration at eye's far accommodation point for reliable vision correction and vision diagnosis.
In addition to measuring wave aberration in an eye, wavefront sensors for the eye can be further configured as a single, cost-effective, mutifunctional workstation for comprehensive vision diagnosis that includes measuring light scattering in the eye and measuring lenses as a lensometer.
Further details of prior eye imaging devices may be found in Liang et al. “Objective measurement of wave aberrations of the human eye with the use of a Hartmann-Shack wave-front sensor,” J. Opt. Soc. Am. A, vol. 11, no. 7, p. 1949, 1994; Liang and Williams “Aberrations and retinal image quality of the human eye,” J. Opt. Soc. Am. A, vol. 14, no. 11, p. 2873, 1997, Westheimer et al. “Evaluating diffusion of light in the eye by objective means” Investigative Ophthalmology & Visual Science, vol. 35, p2652, 1994.
The present invention is directed to an apparatus for measuring wave aberration of an eye. The apparatus comprises an illumination light source configured to produce a compact light source at the retina of the eye, a small opaque stop configured to block corneal reflection of the illumination light, and a wavefront sensor configured to measure the outgoing wavefront originated from the compact light source at the retina.
In another aspect, the present invention is directed to a method for wavefront sensing of human eye with a Hartmann-Shack sensor. The method comprises the steps of producing a compact light source at retina of the eye, receiving the light reflected from the retina with a Hartmann-Shack sensor, wherein the Hartmann-Shack sensor contains a fixed, localized mark for the unique identification of each focus spot to its corresponding lenslet, determining coordinates of focus spots in the wavefront image, calculating wavefront slopes from the displacements of each focus spots, and deriving wave aberration of the eye from the calculated wavefront slopes.
In an additional aspect, the present invention is directed to an apparatus for determining a wave aberration of an eye at its far accommodation point. The apparatus comprises a wavefront module configure to measure wave aberration of an eye, a refraction correction module configured for determining a manifest refraction of the eye subjectively, and a wavefront fusion algorithm for the determination of a wave aberration of the eye at its far accommodation point by combining the measured wavefront aberration from the wavefront module and the manifest refraction from the refraction module.
In yet anther aspect, the apparatus for measuring wave aberrations of an eye further includes measuring light diffusion in an eye, comprising a wavefront sensor module configured for measuring wave aberration of the eye, a refractive correction module configured for a refractive correction of conventional sphero-cylindrical error, a double-pass module configured for measuring a double-pass point-spread distribution of the eye, and a metrics for qualifying the light diffusion in the eye based on the data from the double-pass module.
In yet an additional aspect, the apparatus for measuring wave aberrations of an eye further includes measuring lenses as a lensometer, comprising a light source configured to produce a compact light source at the retina when an eye is measured for its aberrations, a second light source configured to produce a wavefront through a lens when the lens is measured, an optical relay for transferring the measured wavefronts to a plane with a wavefront sensor, a Hartmann-Shack sensor for measuring either a wavefront from an eye under test or a wavefront through a lens under test.
The details of one or more embodiments are set forth in the accompanying drawings and in the description below. Other features, objects, and advantages of the invention will become apparent from the description and drawings, and from the claims.
a shows the distribution of light reflected from the retina in a wavefront system with a Hartmann-Shack sensor.
b shows the distribution of light reflected from the corneal of the eye in a wavefront system with a Hartmann-Shack sensor, and a small opaque stop placed near the conjugate plane of the cornea for blocking the corneal reflection during wavefront measurements in accordance with the present invention.
c shows a schematic diagram of a Hartmann-Shack sensor with at least one lenslet blocked by a small opaque stop.
a shows a configuration for blocking corneal reflection with a small opaque stop that is vertex-centered in accordance to the present invention.
b shows a configuration for blocking corneal reflection with a small opaque stop that is placed at an optical image of corneal reflection in a plane conjugate to the cornea in accordance to the present invention.
a shows ambiguity in identifying focus spots of a wavefront image to their corresponding lenslets for an unrestricted lenslet array.
b shows a localized mark, indicated as the removal of at least one lenslet in the lenslet array, for unique identification of focus spots to their corresponding lenslets in the lenslet array in accordance to the present invention.
a shows a schematic diagram of a wavefront sensor configured for measuring wave aberration of an eye.
b shows a schematic diagram of a wavefront sensor in
The method for blocking the corneal reflex with a small opaque stop shown in
For a more detailed discussion, two cases of probing beams 401 are shown in
For the vertex-centered reflex rejection, a preferred embodiment may include the following features. First, a small opaque stop is placed and bound to an optical flat. The optical flat is chosen because it has no or little impact on the measured wavefront. The opaque stop is small enough (˜0.5 mm) so that at most very few lenslets will be blocked for measuring wavefront from the eye in eye's pupil. Second, the opaque stop can be adjusted with the optical flat in three dimensions in the initial system setup. Along the optical axis, the opaque stop is placed in a conjugate plane of the corneal focal point. In the plane perpendicular to the optical axis, the stop is positioned to block only at most a few fixed lenslets around the optical axis. Third, an alignment mark capable of indicating the location of the opaque stop in the corneal plane is placed in the live images of a pupil camera for pupil alignments. Fourth, the vertex of the cornea is aligned so that the opaque stop can block the corneal reflex. Fifth, wavefront measurements at the missing points can be interpolated or extrapolated according the wavefront slopes next to the missing sampling locations.
Even though collimated illumination beams are illustrated in
b shows another embodiment of blocking the corneal reflex with an opaque stop 414 when a narrow beam 411 is used for producing a compact light source at the retina. Two cases of probing beams are also considered: ON-Vertex-Illumination (ONVI) with a small beam covering the corneal vertex, and OFF-Vertex Illumination (OFFVI) with a small beam not covering the vertex. For both cases, the beam size at the corneal plane is the same for the incoming illumination beam and for the reflected beam, but at different angles of incidence. After imaged through the relay system (L1 and L2), the images of the corneal reflex is fixed and determined by the position of the illumination beam in the wavefront sensor. If a small opaque stop is placed at the conjugate plane of the cornea and covers the image of the corneal reflex entirely, the corneal reflex can be blocked completely. We call this method beam-conjugated reflex rejection because it uses an opaque stop at a conjugate image of the illumination beam.
A preferred embodiment of the beam conjugated approach may include the following features. First, a small beam at the corneal plane is used for the illumination. The beam size should be small enough so that the image of the illumination beam covers very few lenslets in the wavefront sensor plane. Second, a small opaque stop, comparable to the illuminated area at the corneal plane, is placed and bound to an optical flat whose position is adjustable in three axes (x-y-z) in the initial system setup. Along the optical axis, the opaque stop is positioned in the plane conjugate or the lenslet array or next to the lenslet array. In the plane perpendicular to the optical axis, the opaque stop is positioned to block the corneal reflex of the illumination beam and a few fixed lenslets around the optical axis. Alternatively, an opaque stop can be placed and bound to the lenslet array. Third, the small opaque stop will only block wavefront measured at a limited number of lenslets. Wavefront slopes at those missing points can be interpolated or extrapolated according the wavefront slopes next to the missing sampling locations.
Even though our vertex-centered and beam-conjugate methods works fine for both on-vertex illumination and off-vertex illumination, on-vertex illumination is preferred because it will be less sensitive to position errors for the opaque stop. The vertex-centered reflex rejection works better for an illumination beam size larger than 1 mm while the beam-conjugated reflex rejection works better for a small illumination beam size less than 1 mm. Both vertex-centered and beam-conjugated reflex rejections are tolerable to beam position to the cornea vertex because the off-vertex illumination works just fine as the on-vertex illuminations.
Wavefront sensors using a Hartmann-Shack sensor measure wave aberration by converting phase errors across pupil of an eye to displacements of focus spots between a reference image and an image from a test object. Sensing wavefronts requires two measurements: one reference measurement from a known reference such as a perfect plane wave and one measurement from a tested object. If a large unrestricted lenslet array is used for wavefront measurement, unique registration of each focus spot to its corresponding lenslet is almost impossible as shown in
One preferred embodiment for making a registration mark in the lenslet array is to block at least one lenslet in an otherwise unrestricted 2 dimensional lenslet array as shown in
Removing systematic wavefront error is possible when all focus spots in the wavefront measurement are correctly registered to the corresponding lenslets. It can be achieved using the following steps. First, a background measurement with a known wavefront such a plane wave coving a large pupil area is taken as the reference. Second, focus spots in the reference image are uniquely registered to the corresponding lenslets according to a localized feature such as the missing lenslets, and the coordinates of each lenslet for the reference wavefront are stored as the reference coordinates. Third, wavefront slopes for the measured eye at each lenslet are derived from the difference between the corresponding focus spots in the reference and in the wavefront measurement of the eye. Wave aberration of the eye with background error removed can be obtained by reconstructing the wavefront from the obtained wavefront slopes.
Another advantage of unique identification of focus spots to their corresponding lenslets is the accurate registration of the detected wavefront map to the natural pupil of the eye. In a typical wavefront measurement, pupil images as well as wavefront sensor images are obtained with two separate cameras. Because coordinates of the lenslet array and the pupil camera can be precisely determined, wavefront map can be accurately registered to natural pupils of eyes if the obtained wavefront is precisely registered to the lenslet array. Ability to register the measured wavefront to the natural pupil of an eye is critical to the success of a wavefront guided vision correction such as laser vision corrections.
Conventional wavefront sensors usually measure wave aberration of an eye at one accommodation state. Because human eyes do not necessarily accommodate at its far accommodation state during a wavefront measurement, refractive corrections based on the wavefront along can be problematic.
The wavefront module 602 provides a conventional objective wavefront measurement. A narrow illumination beam from a light source LS produces a compact light source. The probing light is diffusely reflected by the retina, from which a distorted wavefront is formed at the eye's cornea plane. An optical relay system, consisting of lenses (L1) and (L2), relays the outgoing wavefront from the eye through the beamsplitter to the plane of a lenslet array. A Hartmann-Shack wavefront sensor, consisting of a lenslet array and an image sensor, provides measurement of wave aberration in the eye.
The refraction module 603 provides corrections of defocus and astigmatism in the eye. In a preferred embodiment, two cylindrical lenses have the cylindrical power of about −3D at the eye's cornea. By rotating the two cylindrical lenses to angles of α and β, respectively, the cylindrical lenses can generate astigmatic correction of up to −6D in any direction plus a focus error DsA(r). By changing the distance (d) between two spherical lenses, the refraction module can generate correction for eye's sphero-cylindrical corrections. The settings of the refractive corrections (α, β, d) are first determined based on a wavefront sphero-cylindrical correction in the tested eye determined from the wave aberration from the wavefront sensor, and further controlled by operators based on patient's reading of a distant (>3 meters) acuity target 604. Manifest refraction as well as visual acuity of the eye is measured using an iterative strategy in standard optometric practice.
The wavefront fusion algorithm, described in U.S. patent application Ser. No. 11/432,273, titled “Wavefront Fusion Algorithms for Refractive Vision Correction and Vision Diagnosis,” filed on May 10, 2006 by J. Liang, provides wave aberration of the tested eye at its far accommodation state by combining the wave aberrations measured with the wavefront module and the manifest refraction from the refractive correction module. First, a wavefront spherical error and cylindrical error is determined from the measured wave aberration of the eye. Second, wave aberration at the far accommodation point of an eye is determined by adding an accommodation offset to the measured wave aberration. The accommodation offset is the difference between the manifest spherical power and the wavefront spherical power.
Even though wavefront sensors measures all aberrations in an eye, it still cannot provide a complete description of eye's optical performance because light scattering in the eye is not measured by a conventional wavefront sensor. Light scattering in the eye is caused by scattering centers at microscopic scale and can produce image blur similar to aberration-induced blur. The image blur caused by aberrations distributes in the central portion of the PSF whereas the light scattering spread light blur to a long pedestal in the eye's point-spread function. Westheimer et al described an Index of Light Diffusion (ILD) for the assessment of light scattering in the eye in “Evaluating diffusion of light in the eye by objective means” Investigative Ophthalmology & Visual Science, vol. 35, p2652, 1994. By incorporating an improve measurement of ILD,
A preferred embodiment of the apparatus comprises a wavefront sensor module 710 configured for measuring wave aberration of the eye, wherein the wave aberrations is represented by a wavefront refraction (the sphero-cylindrical errors) and high-order aberrations in the eye, a refractive correction module 720 configured for correcting the conventional sphero-cylindrical errors based on the wavefront refraction from the wavefront module, a double-pass module 730 configured for measuring light scattering in the eye based on a double-pass measurement of eye's point-spread distribution.
The preferred metrics for measuring light scattering in the eye is the Index of Light Diffusion (ILD) proposed by Westheimer et al. As shown in
A number of improvements are introduced beyond the method proposed in Westheimer et al. First, the ILD measurement is performed after an effective correction for both spherical and astigmatic error in the eye. More particularly, the sphero-cylindrical correction is measured with a wavefront sensor and the sphero-cylindrical correction is achieved by a sphero-cylindrical correction module 720. The effective correction for both the spherical error and the astigmatic error is critical for the ILD measurement because it can ensure that the light energy outside the central region (Io) in the double-pass PSF are indeed due to light scattering only. Second, measurements of ILD are achieved without the influence of the corneal reflection. The method of vertex-centered reflex rejection is incorporated into the ILD measurement using an opaque stop 731. The lens pair (L5 and L6) reproduces the corneal reflection at the opaque stop 731 through a beamsplitter. Third, the ILD measurement is obtained using one light detector (D) with apertures of variable sizes 732. One detector instead of a CCD image sensor is cheaper and can measure the light in the central double-pass PSF (Ic) with a smaller aperture while measures the total light in the double-pass PSF (It) with a larger aperture (or opened completely). ILD of the eye can be derived as (It−Ic)/Ic. Fourth, the ILD measurement can be further improved by using a modulated light source (LS2) so that the ambient background light can be removed by filtering out the DC components in the electric signal from the detector. Fifth, the ILD can be measured at a series of different focus settings that is achieved by setting different focus through the sphero-cylindrical correction module 720, and the smallest ILD is selected as the final measurement of the light diffusion in the eye. Using the smallest ILD through focus guarantees the best correction of eye's focus error, which can be different from the wavefront sphero-cylindrical correction.
Wavefront sensors measures wave aberrations of eye for refractive correction and vision diagnosis. Building a combined lensometer and a wavefront sensor is highly desired in clinical settings. First, a combined system requires less office space and can be cheaper than two separate systems. Second, measuring lenses with a wavefront sensor allows evaluations of correction lenses beyond the conventional sphero-cylindrical correction.
When the system is used for measuring aberrations in an eye as shown in
When the system is used for measure a lens as a lensometer as shown in
A number of embodiments have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the inventions. For example, advantageous results still could be achieved if steps of the disclosed techniques were performed in a different order and/or if components in the disclosed systems were combined in a different manner and/or replaced or supplemented by other components. Accordingly, other embodiments are within the scope of the following claims.
The present invention claims priority to the provisional U.S. patent application No. 60/718,858, titled “Methods and Apparatus for Comprehensive Diagnosis of Human Vision,” filing on Sep. 19, 2005 by J. Liang. The present invention is related to commonly assigned U.S. patent application Ser. No. 11/293,611, titled “Methods and Apparatus for Wavefront Sensing of Human Eyes” filed on Dec. 2, 2005 by J. Liang, U.S. patent application Ser. No. 11/293,612, titled “Methods and systems for wavefront analysis” filed on Dec. 2, 2005 by J. Liang and D. Zhu, U.S. patent application Ser. No. 11/371,288, titled “Algorithms and Methods for Determining Aberration-Induced Vision Symptoms in the Eye from Wave Aberration,” filed on Mar. 8, 2006 by J. Liang, U.S. patent application Ser. No. 11/370,745, titled “Methods for Specifying Image Quality of Human Eyes from Wavefront Measurements,” filed on Mar. 8, 2006 by J. Liang, U.S. patent application Ser. No. 11/432,273, titled “Wavefront Fusion Algorithms for Refractive Vision Correction and Vision Diagnosis,” filed on May 10, 2006 by J. Liang, and U.S. patent application Ser. No. 11/432,274, titled “Multitask Vision Architecture for Refractive Vision Corrections,” filed on May 10, 2006 by J. Liang. The disclosures of these related applications are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60718858 | Sep 2005 | US |
