Optics: eye examining – vision testing and correcting – Eye examining or testing instrument – Objective type
Reexamination Certificate
2001-04-27
2004-06-08
Manuel, George (Department: 3737)
Optics: eye examining, vision testing and correcting
Eye examining or testing instrument
Objective type
Reexamination Certificate
active
06746121
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to optical instruments and, more particularly, to a method and device for defocus and astigmatism compensation in wavefront aberration measurement systems. The present invention is particularly useful, but not exclusively so, for defocus and astigmatism compensation in ophthalmic applications.
BACKGROUND OF THE INVENTION
The human eye is an optical system employing several lens elements 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 the desired path. These deviations, referred to as aberrations, result in blurred images and decreased visual acuity. Hence, methods and apparatuses for measuring aberrations are desirable to aid in the correction of such problems.
One method of detecting aberrations introduced by the eye involves determining the aberrations of light rays exiting from 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, with the wavefront containing aberrations introduced by the eye. By determining the propagation direction of discrete portions (i.e., samples) of the wavefront, the aberrations introduced by the eye can be determined and corrected.
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
14
of an eye
16
. The laser beam
12
focuses to a small spot
18
on the retina
14
. The retina
14
, acting as a diffuse reflector, reflects the laser beam
12
, resulting in the point source wavefront
10
. Ideally, the wavefront
10
would be represented by a planar wavefront
20
. However, aberrations introduced by the eye
16
as the wavefront
10
passes out of the eye
16
result in an imperfect wavefront, as illustrated by the aberrated wavefront
20
A. 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 lenses 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
24
. The laser beam
12
forms a spot
18
on the retina
14
of the eye
16
. The retina
14
reflects the light from the spot
18
to create a point source wavefront
10
which becomes aberrated as it passes through the lens and other components and materials within the eye
16
. The wavefront
10
then passes through a first lens
11
and a second lens
13
to focus the wavefront
10
so that the wavefront
10
is collimated. The wavefront
10
then passes through the beam splitter
24
toward a wavefront sensor
26
. Information detected by the wavefront sensor
26
is then processed by a processor
27
to determine the aberrations of the wavefront
10
.
FIG. 3
illustrates the focusing of the wavefront
10
to produce a flat wavefront for projection onto the wavefront sensor
26
. If the wavefront
10
contains diverging light, the light rays which make up the wavefront
10
would continue to diverge until they were no longer contained within the system, thereby losing valuable wavefront
10
information. This is especially problematic for an eye
16
having a large degree of defocus. In
FIG. 3
the curved wavefront
10
A containing diverging light rays passes through the first lens
11
where it converges to a crossover point
15
, and then through the second lens
13
. When the crossover point
15
occurs at one focal length before the second lens
13
, the resultant wavefront
10
B will be collimated (i.e., flat). For different degrees of defocus, the lenses
11
and
13
can be moved relative to one another in order for the focal point of lens
13
to match the cross-over point
15
. Unfortunately, for an eye
16
having a great deal of defocus, the lenses
11
and
13
may need to be moved a relatively large distance from one another, which may be problematic if space is limited. In addition, the defocus mechanism of
FIG. 3
does not correct other eye aberrations such as astigmatism in which light along one axis converges/diverges more rapidly than light along another axis. Since the lenses
11
and
13
converge or diverge light along every axis equally, this arrangement does not compensate for astigmatism.
Typical wavefront sensors
26
include either an aberroscope
28
(
FIG. 4
) or a Hartman-Shack lenslet array
30
(FIG.
5
), with an imaging device
32
. The aberroscope
28
and the Hartman-Shack lenslet array
30
each produce an array of spots when a wavefront passes through them. The imaging device
32
contains an imaging plane
34
for capturing the spots generated by the aberroscope
28
or the Hartman-Shack Sensor
30
. Generally, the imaging device
32
is a charge coupled device (CCD) camera.
The wavefront sensor
26
samples the wavefront
10
by passing the wavefront
10
through the aberroscope
28
or the Hartman-Shack sensor
30
, resulting in an array of spots on the imaging plane
34
. Each spot on the imaging plane
34
represents a portion of the wavefront
10
, with smaller portions enabling the aberrations to be determined with greater accuracy. By comparing the array of spots produced on the imaging plane
34
by the wavefront
10
with a reference array of spots corresponding to the wavefront of an ideal eye, the aberrations introduced by the eye
16
can be computed.
An example of a Hartman-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, is incorporated herein by reference.
The resolution of the aberrations in such prior art devices, however, is limited by the sub-aperture spacing
36
and the sub-aperture size
38
in an aberroscope sensor (see FIG.
4
), and by the lenslet sub-aperture size
40
and focal length in a Hartman-Shack sensor (see FIG.
5
). In addition, large aberrations due to excessive defocus or astigmatism may result in foldover. Foldover occurs in an aberroscope sensor, for example, when two or more spots
42
A,
42
B, and
42
C on the imaging plane
34
overlap, thereby leading to confusion between adjacent sub-aperture spots. Similarly, foldover occurs in Hartman-Shack sensors when two or more spots
44
A,
44
B,
44
C, and
44
D on the imaging plane
34
overlap. Typical systems are designed to accommodate a certain amount of defocus and astigmatism, however, these systems are unable to handle defocus and astigmatism of individuals with large astigmatism and/or large defocus.
Foldover may result from a sub-aperture spacing
36
, sub-aperture size
38
, or lenslet size
40
which is too small, a high degree of aberration (e.g., large defocus and/or astigmatism); or a combination of these conditions. Hence, the sub-aperture spacing
36
and sub-aperture size
38
in the aberroscope sensor (FIG.
4
), and the lenslet sub-aperture spacing
40
and focal length in the Hartman-Shack sensor (
FIG. 5
) must be selected 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/or dynamic range and vice versa.
The constraints imposed by the aberroscope and Hartman-Shack approaches limit the effectiveness of these systems for measuring wavefronts having a wide range of aberrations, such as those exhibiting a large degree of defocus and astigmatism. These
Baschek Bjoern
Bille Josef
Ross Denwood F.
Schottner Michael
Gianneschi Lois A.
Manuel George
LandOfFree
Defocus and astigmatism compensation in a wavefront... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Defocus and astigmatism compensation in a wavefront..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Defocus and astigmatism compensation in a wavefront... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3295767