Ophthalmic wavefront measuring devices

Optics: eye examining – vision testing and correcting – Eye examining or testing instrument – Objective type

Reexamination Certificate

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C250S201900, C351S246000

Reexamination Certificate

active

06827442

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to optical instruments for measuring eye aberrations in a patient and, more particularly, to apparatuses and methods for modifying the input beam entering the patient's eye, patient corrective prescription verification, and binocular vision correction in ophthalmic wavefront measuring systems.
BACKGROUND OF THE INVENTION
The eye is an optical system having several lens elements for focusing 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 used to aid in the correction of such problems.
One method of detecting aberrations introduced by the eye involves the determination of aberrations introduced into light rays when exiting from the eye. An input beam of light focused into the eye to 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 this wavefront, the aberrations introduced by the eye can be determined. The determined aberrations can then be used to produce corrective lenses and/or perform corrective procedures that restore visual acuity.
A general illustration of the generation of a wavefront is shown in
FIG. 1. A
wavefront
100
is generated by reflecting an input beam
102
off of the retina
104
of an eye
106
. The input beam
102
focuses to a small spot
108
on the retina
104
. The retina
104
, acting as a diffuse reflector, reflects the input beam
102
, resulting in the wavefront
100
. Ideally, the wavefront
100
would be free of aberrations, as illustrated by the planar wavefront
110
. However, aberrations introduced by the eye
106
as the wavefront
100
passes out of the eye
106
result in an imperfect wavefront, as illustrated by the aberrated wavefront
112
. The wavefront
100
represents aberrations due to defocus, astigmatism, coma, spherical aberrations, and other irregularities. Measuring and correcting the aberrations allow the eye
106
to approach its full potential, i.e., the limits of visual resolution.
FIG. 2
is an illustration of a prior art ophthalmic wavefront measuring device for measuring aberrations within the wavefront
100
as illustrated in
FIG. 1. A
radiation source
114
(e.g., a laser) generates the input beam
102
which is routed to the eye
106
by a beam splitter
116
. Typically, the input beam
102
generated by the radiation source
114
is substantially circular. The input beam
102
forms a spot
108
on the retina
104
of the eye
106
. In an eye
106
free of imperfections, the spot
108
formed on the retina
104
is circular. Due to imperfections within the eye
106
, the input beam
102
becomes aberrated, thereby resulting in the spot
108
formed on the retina
104
having a non-circular shape as illustrated in FIG.
2
A. As will be discussed below, a retinal spot
108
with a non-circular shape affects adversely the determination of aberrations due to imperfections within the eye
106
. The retina
104
then reflects the light from the spot
108
to create a wavefront
100
which is aberrated as it passes through the lens and other components and materials within the eye
106
.
On the return path, the wavefront
100
passes through the beam splitter
116
toward a sensor
118
. A quarter-wave plate
120
is positioned between the eye
106
and the beam splitter
116
. The use of a quarter-wave plate
120
is a known technique for manipulating the polarization of the input beam
102
going into the eye
106
and the wavefront
100
emanating from the eye
106
so that the wavefront
100
is polarized in a direction perpendicular to the input beam
102
, thereby enabling the wavefront
100
to pass through the beam splitter
116
toward the sensor
118
. Additional lenses
122
are positioned between the eye
106
and the sensor
118
to image the plane of the pupil of the eye
106
onto the sensor
118
with a desired magnification. Information detected by the sensor
118
is then processed by a processor
124
to determine the aberrations of the wavefront
100
and determine a corrective prescription for the eye
106
.
A typical sensor
118
includes a Hartman-Shack lenslet array
126
and an imaging device
128
containing an imaging plane
130
such as a charge coupled device (CCD) array. The lenslet array
126
samples the wavefront
100
and produces an array of spots
132
on the imaging plane
130
, as illustrated in
FIG. 2B
, when the wavefront
100
passes through it. Each spot within the array of spots
132
is an image of the retinal spot
108
. The relative positions of each spot within the array of spots
132
can be used to determine the aberrations of the wavefront
100
.
Typically, the aberrations of the wavefront
100
are determined by determining an aberration for each sample of the wavefront
100
which are then combined. The determined aberrations are then used to calculate a corrective prescription for the eye
106
.
The aberration of each sample of the wavefront
100
is determined by determining the centroid of a spot within the array of spots
132
and comparing the displacement between the centroid of the spot with a corresponding reference location, such as the location represented by reference spot
134
. Since each spot within the array of spots
132
is an image of the retinal spot
108
, if the retinal spot
108
is non-circular, as illustrated in
FIG. 2A
, each spot within the array of spots
132
will be non-circular, as illustrated in FIG.
2
B.
Determining the centroid of a non-circular spot, however, is difficult, requiring significant processing time and power. Accordingly, since determining the centroid of the spots within the array of spots
132
is a prerequisite to determining the aberrations in the wavefront
100
, and determining the centroid of a non-circular spot is difficult, non-circular spots on the imaging plane
130
affect adversely the speed and accuracy of computing aberrations. Therefore, apparatuses and methods for producing circular spots on the imaging plane
130
would be useful.
Another area for improvement is related to the ability of wavefront measuring devices to determine aberrations introduced by the eye
106
with a high degree of accuracy. This accuracy allows the determination of a corrective prescription for a patient that is precisely tailored to the patient's visual needs. The precisely tailored corrective prescriptions, however, cannot be presented to the patient through a series of lenses as is traditionally done in determining corrective prescriptions at an eye doctor for example. This is due to the fact that each precisely tailored corrective prescription is so unique that it would be impossible to recreate the corrective prescription using a series of lenses without specially producing a lens having the corrective prescription. Accordingly, the patient is unable to determine if the corrective prescription determined by the wavefront measuring device satisfies the patient's visual needs until prescription eye wear is produced (e.g., corrective lenses are ground or contact lenses are formed). Therefore, apparatuses and methods for allowing a patient to verify a corrective prescription prior to the production of corrective eye wear would be useful.
Yet another area for improvement is related to the dependancy of aberrations on binocular vision (i.e., viewing an object with both eyes at the same time). Prior art wavefront measuring devices such as the one depicted in
FIG. 2
measure only one eye at a time. Accordingly, the affects of binocular vision on aberrat

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