Optics: eye examining – vision testing and correcting – Eye examining or testing instrument – Methods of use
Reexamination Certificate
2000-10-02
2003-09-09
Manuel, George (Department: 3737)
Optics: eye examining, vision testing and correcting
Eye examining or testing instrument
Methods of use
Reexamination Certificate
active
06616279
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to optical instruments and, more particularly, to a method and apparatus for measuring wavefront aberrations. The present invention is particularly useful, but not exclusively so, for measuring the optical wavefront in ophthalmic applications, e.g., measurement of aberrations of the eye, in corrective devices such as lenses (e.g., contact, spectacle, and intraocular), and for evaluating the ocular aberrations before, during and after refractive surgery to improve vision.
BACKGROUND OF THE INVENTION
The human eye is an optical system which employs a lens to focus light rays representing images onto the retina within the eye. The sharpness of the images produced on the retina is a factor in determining the visual acuity of the eye. Imperfections within the lens and other components and material within the eye, however, may cause the light rays to deviate from a desired path. These deviations, referred to as aberrations, result in blurred images and decreased visual acuity. Hence, a method and apparatus for measuring aberrations is desirable to aid in the correction of such problems.
One method of detecting aberrations introduced by an eye involves determining the aberrations of light rays exiting from within the eye. A beam of light directed into the eye as a point on the retina is reflected or scattered back out of the eye as a wavefront. The wavefront represents the direction of light rays exiting from the eye. By determining the propagation direction of individual portions of the wavefront, the aberrations introduced to the light rays passing through parts of the eye such as the cornea can be determined and corrected. In this type of system, increased accuracy in determining the aberrations can be achieved by reducing the size of the regions of the wavefront used to derive the propagation direction.
A general illustration of the generation of a wavefront is shown in FIG.
1
.
FIG. 1
is a schematic view of a wavefront
10
generated by reflecting a laser beam
12
off of the retina
20
of an eye
16
. The laser beam
12
focuses to a small spot
14
on the retina
20
. The retina
20
, acting as a diffuse reflector, reflects the laser beam
12
, resulting in a point source wavefront
10
. Ideally, the wavefront
10
from a point source leaving a perfect eye would be represented by a spherical or planar wavefront
22
. However, aberrations introduced by the eye
16
as the wavefront passes out of the eye result in an imperfect wavefront, as illustrated by the wavefront
10
. The wavefront
10
represents aberrations which lead to defocus, astigmatism, spherical aberrations, coma, and other irregularities. Measuring and correcting these aberrations allow the eye
16
to approach its full potential, i.e., the limits of visual resolution.
FIG. 2
is an illustration of a prior art apparatus for measuring the wavefront
10
as illustrated in FIG.
1
. By measuring the aberrations, corrective lens can be produced and/or corrective procedures performed to improve vision. In
FIG. 2
, a laser
22
generates the laser beam
12
which is routed to the eye
16
by a beam splitter
25
. The laser beam
12
forms a spot
14
on the retina
20
of the eye
16
. The retina reflects the light from the spot
14
to create a point source wavefront
10
which becomes aberrated as it passes through the lens and other components and material within the eye
16
. The wavefront
10
passes through the beam splitter
25
toward a wavefront sensor
26
. The apparatus described in
FIG. 2
is commonly described as single-pass wavefront measurement system.
Typical prior art wavefront sensors
26
include either an aberroscope
30
and an imaging plane
28
, as illustrated in
FIG. 3
, or a Hartmann-Shack sensor
40
and an imaging plane
28
, as illustrated in FIG.
4
. The wavefront sensor
26
samples the wavefront
10
by passing the wavefront
10
through the aberroscope
30
or the Hartmann-Shack sensor
40
, resulting in the wavefront
10
producing an array of spots on an imaging plane
28
. Generally, the imaging plane
28
is a charge coupled device (CCD) camera. By comparing an array of spots produced by a reference wavefront to the array of spots produced by the wavefront
10
, the aberrations introduced by the eye
16
can be computed.
Each spot on the imaging plane
28
represents a portion of the wavefront
10
, with smaller portions enabling the aberrations to be determined with greater precision. Thus, the smaller the sub-aperture spacing
32
and the size of the sub-aperture
33
in the aberroscope
30
of
FIG. 3
, and the smaller the lenslet sub-aperture spacing
42
in the Hartmann-Shack sensor
40
of
FIG. 4
, the more accurately the aberrations can be determined.
An example of a Hartmann-Shack system is described in U.S. Pat. No. 6,095,651 to Williams et al., entitled Method and Apparatus for Improving Vision and the Resolution of Retinal Images, filed on Jul. 2, 1999, incorporated herein by reference.
The resolution of the aberrations in such prior art devices, however, is limited by the grid size
32
and aperture size
33
in an aberroscope
30
(see FIG.
3
), and by the lenslet subaperture spacing
42
in a Hartmann-Shack sensor
40
(see FIG.
4
). Due to foldover, reductions to grid size
32
and lenslet sub-aperture spacing
42
are limited. Foldover occurs in an aberroscope sensor
30
, for example, when two or more spots
31
A,
31
B, and
31
C on imaging plane
28
overlap thereby leading to confusion between adjacent sub-aperture spots. Similarly, foldover occurs in Hartmann-Shack sensors
40
when two or more spots
41
A,
41
B,
41
C, and
41
D on imaging plane
28
overlap. Foldover may result from a grid size
32
or lenslet sub-aperture spacing
42
which is too small, a high degree of aberration, or a combination of these conditions. Hence, the grid size
32
or lenslet sub-aperture spacing
42
must be balanced to achieve good spatial resolution while enabling the measurement of large aberrations. Accordingly, the ability to measure a high degree of aberration comes at the expense of spatial resolution and vice versa.
The constraints imposed by the aberroscope and Hartmann-Shack approaches limit the effectiveness of these systems for measuring large aberrations with a high degree of spatial resolution. These limitations prevent optical systems with large aberrations from being measured, thereby preventing them from achieving their full potential. Accordingly, ophthalmic devices and methods which can measure a wide range of aberrations with a high degree of spatial resolution would be useful.
SUMMARY OF THE INVENTION
The present invention discloses an apparatus and method for determining the aberrations of a wavefront with a high degree of accuracy. The apparatus includes a plurality of mirrors for reflecting selected portions of the wavefront, an imaging device for capturing information related to the selected portions, and a processor for controlling the plurality of mirrors and interpreting the captured information to compute the aberrations. The method includes reflecting selected portions of a wavefront onto an imaging device, capturing information related to the selected portions, and processing the captured information to derive the aberrations. The apparatus and method of the present invention are capable of measuring a wide range of aberrations with a high degree of spatial resolution.
The wavefront originates as a point source within a focusing optical system (e.g. the eye). The point source is generated by directing a beam of radiation (e.g., a laser) through the focusing optical system and scattering or reflecting the beam. A beam splitter disposed in the path of the laser beam directs the laser beam through the focusing optical system. The focusing optical system has an interior portion functioning as a diffuse reflector for reflecting or scattering the beam. The wavefront resulting from the point source passes through the focusing optical system and the beam splitter to the wavefront
Collins Michael J.
Davis Brett A.
Iskander Daoud R.
Roffman Jeffrey H.
Ross, III Denwood F.
Johnson & Johnson Vision Care Inc.
Manuel George
LandOfFree
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