# US 4,396,261 A · Method for determining the curvature of a cornea

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- Number: US 4,396,261 A
- Document ID: US4396261A
- Status: Granted
- Kind: A
- Application number: 06/213,608
- Filed: 1980-12-05
- Granted: 1983-08-02
- Earliest claimed: 1980-12-05
- Inventors: M. Linton Herbert
- Web page: https://patentgrep.com/patent/US4396261A

## CPC

- A61B 8/10: Eye inspection
- A61B 3/107: for determining the shape or measuring the curvature of the cornea
- A61B: DIAGNOSIS; SURGERY; IDENTIFICATION (usefulness limited to only animals A61D)

## Abstract

The method of the present invention uses a standard prior art refracting device of the type typically used by an optometrist to refract the human eye in air and in water. Computations utilizing the refraction data obtained during the air and water refraction measurements is used to compute the radius of curvature of the central area of the cornea of a human eye. The method of the present invention thereby substantially facilitates contact lens fitting procedures.

## Claims

### Claim 1

A method for determining the curvature of the central area of the cornea of a human eye to simplify contact lens fitting procedures, comprising the steps of:
a. using a refracting device to determine the corrective refractive power of the eye in air;
b. using said refracting device to determine the corrective refractive power of the eye in a transparent liquid;
c. measuring the spacing between the anterior portion of the cornea and said refracting device;
d. computing the refractive power of the cornea; and
e. using the cornea refractive power to compute the cornea radius of curvature.

### Claim 2 (depends on 1)

The method of claim 1 wherein the cornea includes a centrally located optical zone and a surrounding bearing zone, further comprising the step of selecting a contact lens having a curvature on the rear surface of the central area approximately equal to the radius of curvature of the optical zone of the cornea.

### Claim 3 (depends on 2)

The method of claim 2 further comprising the step of selecting by trial and error a contact lens having a curvature on the rear surface of the bearing zone approximately equal to the curvature of the bearing zone of the cornea.

### Claim 4 (depends on 1)

The method of claim 1 further comprising the step of positioning a liquid filled chamber having an optically flat transparent window on the end thereof over the eye to immerse the cornea in the transparent liquid.

### Claim 5 (depends on 4)

The method of claim 4 wherein the interior of said chamber is filled with a transparent liquid having an index of refraction of approximately 1.336.

### Claim 6

A method for determining the curvature of the central area of the cornea of a human eye to simplify contact lens fitting procedures, comprising the steps of:
a. using a refracting device to determine the corrective refractive power of the eye in the air and in a transparent liquid;
b. measuring the spacing between the anterior portion of the cornea and said refracting device and the spacing between the surface of the cornea and the retina of the eye;
c. computing the refractive power of the cornea; and
d. using the cornea refractive power to determine the radius of curvature of the central area of the cornea.

### Claim 7 (depends on 6)

The method of claim 6 wherein the cornea includes a centrally located optical zone and a surrounding bearing zone, further comprising the step of selecting a contact lens having a curvature on the rear surface of the central area approximately equal to the radius of curvature of the optical zone of the cornea.

### Claim 8 (depends on 7)

The method of claim 7 further comprising the step of selecting by trial and error a contact lens having a curvature on the rear surface of the bearing zone approximately equal to the curvature of the bearing zone of the cornea.

### Claim 9 (depends on 6)

The method of claim 6 further comprising the step of positioning liquid filled goggles over the eye to immerse the cornea in the liquid.

### Claim 10 (depends on 9)

The method of claim 9 wherein the space between said goggles and the eye is filled with a transparent liquid having an index of refraction of approximately 1.336.