Ophthalmic talbot-moire wavefront sensor

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

Reexamination Certificate

Rate now

  [ 0.00 ] – not rated yet Voters 0   Comments 0

Details

Reexamination Certificate

active

06736510

ABSTRACT:

BACKGROUND OF THE INVENTION
Improving eyesight is vitally important. Precise measurement of the eye's physical characteristics, including features of the eye, in order to prescribe vision correction is also vitally important.
With the advent of new technologies capable of creating more complex optical surfaces, a resurgence of interest has arisen in the tools required to measure the eye's optical characteristics to a higher degree of complexity than was possible before.
This invention is an improvement on a system described by U.S. Pat. No. 5,963,300 to Horwitz. In the Horwitz system, a light beam is projected into the eye. The light beam is of a diameter equal to or larger than that of the eye's pupil. The eye focuses the light beam onto the retina, the beam then reflects back out of the eye, through the optical components of the eye. A relay lens system collects the light reflected from the eye, projecting the collected light through a reticle, or a plurality of reticles. A spatial filter (an iris), is positioned within the relay lens system to block unwanted reflected light. The light that passes through the reticle(s), is projected onto a translucent screen to create a image on the screen. A charged coupled device CCD camera is focused onto the screen to “see” the patterns created by the reticle(s). A computer is used to convert the CCD camera images to digital data. The computer then analyzes the data to determine the refractive condition of the eye. The computer also analyzes the position of the reflected glint from the vertex of the cornea as well as the position of the pupil, compares the two positions, and determines where the eye is gazing.
There are several methods available to measure the reflected wavefront of an eye. The method of this invention is known as “Talbot/Moire Interferometry.” Of the other methods available, the most common method is known as a “lenslet array system”,or a “Hartmann Shack” sensor. Such a wavefront sensor is described by Liang et al. in “Objective Measurement of Wave Aberrations of the Human Eye with the Use of a Hartmann-Shack Wave-Front Sensor,” Journal of the Optical Society of America, Vol. 1, No. 7, July 1994, p.p 1949-1957.
One of the earlier Hartmann Shack systems is described by U.S. Pat. No. 5,949,521 to Williams. A light beam is projected into the eye. Williams first passes the light through optical components and then reflects it from a deformable mirror before projecting it into the eye. A relay lens system collects the light reflected from the eye, projecting the collected light onto a deformable mirror, which in turn reflects it to a lenslet array.
A lenslet array is a disc with many, many tiny lenses, much like an insect eye, but flat instead of spherical. The lenslet array creates numerous spots of light focused into aerial images. If the light being collected by a tiny lens approaches the lens “straight on”,then the spot that the tiny lens forms will be along the optical axis of the tiny lens. However, if the light is approaching the tiny lens not “straight on”, but skewed off to one side of the optical axis, then the resulting spot will be formed to one side of the optical axis of the tiny lens. When the reflected light emerging from an eye being analyzed is not perfectly aligned along the optical axis, then the eye has a defect in it. The resulting shift in the position of the spot formed by the tiny lens indicates the type of, and the degree of the defect in the eye. The positions of each of the tiny lenses are related to the optical performance of the corresponding position of the eye. In other words, a tiny lens at the very top of the array that is collecting light emerging from the eye will produce a spot, and subsequent information about the light that emerged from the top of the eye. Conversely, a spot on the bottom of the array corresponds to the bottom of the eye, and so forth. (If the image is inverted or mirrored, as it sometimes is depending upon the optical design, then the relationship must be adjusted accordingly. For example, if the image is inverted, then the “top” of the eye will be represented by a spot on the “bottom” of the array.) A CCD camera is focused onto the aerial plane where the spots come into focus, “seeing” the spots of light. A computer is used to convert the CCD camera images to digital data. The computer then analyzes the data to determine the refractive condition of the eye, by comparing the shift of each spot from where the spot would have been had the eye been defect free. The computer changes the shape of the deformable mirror to alter the resulting spot pattern produced by the lenslet array, attempting to alter it in such a manner to bring the spots closer to the position where the spots would have been for a properly focusing eye.
An improvement on the Hartmann Shack system is described by U.S. Pat. No. 6,270,221 to Liang et al. Liang et al had difficulty relying upon the human eye to focus the incoming large light beam into a small spot on the retina, due to the shortcomings of the Hartmann Shack lenslet system. The very thing that made the Hartmann Shack device useful (measuring eyes with problems focusing), gave it trouble with those eyes. Eyes that did not focus well could not be measured because the reflected wavefront did- not originate from a small spot, it originated from a large spot, degrading the performance of the lenslets. Because the Hartmann Shack system uses lenslets, it is very sensitive to this type of error. The Liang et al solution was to add focusing lenses to converge or diverge the illumination beam to compensate for the refractive deficiencies of the eye, as well as the extreme sensitivity of the Hartmann Shack lenslet system to this problem.
BRIEF DESCRIPTION OF THE INVENTION
Applicant's invention is an improvement on the Horwitz system.
With respect to Horwitz, the light beam projected into the eye, in Applicant's system, is of a diameter much less than the diameter of the eye's pupil. The Horwitz system required that the eye's cornea and lens focus the light into a small point on the surface of the retina. When a patient's eye was working well, a small point of light did form on the retina. However, if a patient's eye was not working well, or was simply accommodating, a small point of light was not formed. Instead, a larger spot of light was formed. The worse the refractive condition of the eye, the larger the spot became. This resulted in light being reflected from the retina from many points, which degraded the image quality of the fringes. The addition of a spatial filter and screen helped filter out many of the unwanted reflections, but not all. More importantly though, the spatial filter placed a limit on the :measurement range of the device, and the screen reduced its sensitivity to some higher order aberrations. Reduced sensitivity to these higher order aberrations may have been acceptable, and even desirable at the time of the Horwitz invention, but now it is desirable to measure and quantify them. Additionally, the measurement range of the previous device was acceptable in its time, but now higher measurement range demands are being placed on these systems, and more range is required.
By using a beam diameter much smaller than the eye's pupil diameter, such as less than 1 mm, the beam passes through the central axis of the eye, where virtually no refraction takes place. Regardless of the optical performance of the patient's eye, or its accommodative state, the light still forms into a small spot on the retina, which results in a much better quality return signal for purposes of fringe pattern generation. Small illumination beam diameters may also be projected into the eye from other angles and positions, so long as they impinge upon the retina at the point corresponding to the central optical axis.
No topography or pachymetry is employed. Applicant's invention only analyzes the light reflected from the retina and refracted through all the optical components of the eye. It does not ana

LandOfFree

Say what you really think

Search LandOfFree.com for the USA inventors and patents. Rate them and share your experience with other people.

Rating

Ophthalmic talbot-moire wavefront sensor does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Ophthalmic talbot-moire wavefront sensor, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Ophthalmic talbot-moire wavefront sensor will most certainly appreciate the feedback.

Rate now

     

Profile ID: LFUS-PAI-O-3219204

  Search
All data on this website is collected from public sources. Our data reflects the most accurate information available at the time of publication.