Optics: eye examining – vision testing and correcting – Eye examining or testing instrument – Objective type
Reexamination Certificate
2001-08-31
2003-07-22
Manuel, George (Department: 3737)
Optics: eye examining, vision testing and correcting
Eye examining or testing instrument
Objective type
Reexamination Certificate
active
06595642
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to ophthalmic instruments that are used to examine or treat the eye, including ophthalmic examination instruments (such as phoropters and autorefractors) that measure and characterize the aberrations of the human eye in order to prescribe compensation for such aberrations via lens (such as glasses or contact lens) or surgical procedure (such as laser refractive surgery), in addition to ophthalmic imaging instruments (such as fundus cameras, corneal topographers, retinal topographers, corneal imaging devices, and retinal imaging devices) that capture images of the eye.
2. Summary of the Related Art
The optical system of the human eye has provided man with the basic design specification for the camera. Light comes in through the cornea, pupil and lens at the front of the eye (as the lens of the camera lets light in). This light is then focused on the inside wall of the eye called the retina (as on the film in a camera). This image is detected by detectors that are distributed over the surface of the retina and sent to the brain by the optic nerve which connects the eye to the brain (as film captures the image focused thereon).
FIG. 1
shows a horizontal cross section of the human eye. The eye is nearly a sphere with an average diameter of approximately 20 mm. Three membranes—the cornea and sclera outer cover, the choroid and the retina—enclose the eye. The cornea
3
is a tough transparent tissue that covers the anterior surface of the eye. Continuous with the cornea
3
, the sclera
5
is an opaque membrane that encloses the remainder of the eye. The choroid
7
lies directly below the sclera
5
and contains a network of blood vessels that serves as the major source of nutrition to the eye. At its anterior extreme, the choroid
7
includes a ciliary body
9
and an iris diaphragm
11
. The pupil of the iris diaphragm
11
contracts and expands to control the amount of light that enters the eye. Crystalline lens
13
is made up of concentric layers of fibrous cells and is suspended by fibers
15
that attach to the ciliary body
9
. The crystalline lens
13
changes shape to allow the eye to focus. More specifically, when the ciliary muscle in the ciliary body
9
relaxes, the ciliary processes pull on the suspensory fibers
15
, which in turn pull on the lens capsule around its equator. This causes the entire lens
13
to flatten or to become less convex, enabling the lens
13
to focus light from objects at a far away distance. Likewise, when the ciliary muscle works or contracts, tension is released on the suspensory fibers
15
, and subsequently on the lens capsule, causing both lens surfaces to become more convex again and the eye to be able to refocus at a near distance. This adjustment in lens shape, to focus at various distances, is referred to as “accommodation” or the “accommodative process” and is associated with a concurrent constriction of the pupil.
The innermost membrane of the eye is the retina
17
, which lies on the inside of the entire posterior portion of the eye. When the eye is properly focused, light from an object outside the eye that is incident on the cornea
3
is imaged onto the retina
17
. Vision is afforded by the distribution of receptors (e.g., rods and cones) over the surface of the retina
17
. The receptors (e.g., cones) located in the central portion of the retina
17
, called the fovea
19
(or macula), are highly sensitive to color and enable the human brain to resolve fine details in this area. Other receptors (e.g., rods) are distributed over a much larger area and provides the human brain with a general, overall picture of the field of view. The optic disc
21
(or the optic nerve head or papilla) is the entrance of blood vessels and optic nerves from the brain to the retina
17
. The inner part of the posterior portion of the eye, including the optic disc
21
, fovea
19
and retina
17
and the distributing blood vessels is called the ocular fundus
23
. Abnormalities in the cornea and crystalline lens and other portions of the eye contribute to refractive errors (such as defocus, astigmatism, spherical aberrations, and other high order aberrations) in the image captured by the retina.
A phoropter (or retinoscope) is an ophthalmic instrument that subjectively measures the refractive error of the eye. A typical phoropter consists of a pair of housings in which are positioned corrective optics for emulating the ophthalmic prescription required to correct the vision of the patient whose eyes are being examined. Typically, each housing contains sets of spherical and cylindrical lenses mounted in rotatable disks. The two housings are suspended from a stand or wall bracket for positioning in front of the patient's eyes. Further, in front of each refractor housing a number of accessories are mounted, typically on arms, so that they may be swung into place before the patient's eyes. Typically, these accessories include a variable power prism known as a Risley prism, Maddox rods, and a cross cylinder for performing the Jackson cross cylinder test. In determining a patient's distance prescription, the patient views a variety of alpha numeric characters of different sizes through various combinations of the spherical and/or cylindrical lenses supported in the refractor housings until the correct prescription is emulated. The characters, which are typically positioned 6 meters away, may be on a chart or may be projected on a screen by an acuity projector. For near vision testing, the same procedure is repeated, expect that the alpha numeric characters viewed by the patient are positioned on a bracket 20 to 65 centimeters in front of the refractor housing. The cross cylinder is used to refine the power and axis position of the cylindrical component of the patient's prescription. The cross cylinder is a lens consisting of equal power plus and minus cylinders with their axes 90 degrees apart. It is mounted in a loupe for rotation about a flip axis which is midway between the plus and minus axes.
An autorefractor is an ophthalmic instrument that quantitatively measures the refractor errors of the eye. Light from an illumination source (typically an infra-red illumination source) is directed into the eye of the patient being examined. Reflections are collected and analyzed to quantitatively measure the refractive errors of the eye.
Conventional phoropters and autorefractors characterize the refractive errors of the eye only in terms of focal power (typically measured in diopter) required to compensate for such focal errors; thus, such instruments are incapable of measuring and characterizing the higher order aberrations of the eye, including astigmatism and spherical aberration. Examples of such devices are described in the following U.S. Pat. Nos. 4,500,180; 5,329,322; 5,455,645; 5,629,747; and 5,7664,561.
Instruments have been proposed that utilize wavefront sensors to measure and characterize the high order aberrations of the eye. For example, U.S. Pat. No. 6,007,204, to Fahrenkrug et al. discloses an apparatus for determining refractive aberrations of the eye wherein a substantially collimated beam of light is directed to the eye of interest. This collimated light is focused as a secondary source on the back of the eye, thereby producing a generated wavefront that exits the eye along a return light path. A pair of conjugate lenses direct the wavefront to a microoptics array of lenslet elements, where incremental portions of the wavefront are focuses onto an imaging substrate. Deviation of positions of the incremental portions relative to a known zero or “true” position (computed by calculating the distance between the centroids of spots formed on the imaging substrate by the lenslet array) can be used to compute refractive error relative to a known zero or ideal diopter value. Because the optical power at the lenslet does not equal the optical power of the measured eye, the optical power of the lenslet is corrected by the conjugate lens mapping
Adaptive Optics Associates, Inc.
Manuel George
Thomas J. Perkowski Esq., P.C.
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