Contact lens for keratoconus
The present invention is directed to a non-deforming contact lens for keratoconus patients having a displaced central zone. In particular, the central zone is displaced from the geometric center of the lens. The shape of the central zone is egg or spoon-shaped and is rotationally asymmetrical with one semi-meridian that is shorter than a corresponding semi-meridian. An intermediate transition zone is formed integral with the periphery of the central zone, and a peripheral zone is formed integral with the periphery of the intermediate transition zone, forming a round contact lens.
1. A method of fitting a contact lens for keratoconus, comprising:
determining a central keratometry measurement of a patient's eye;
using the central keratometry measurement to determine an apical radius of the contact lens;
using the central keratometry measurement to determine an amount of displacement of an apex of a cornea of the eye; and
basing a posterior surface geometry of the contact lens on known mean biometric values;
wherein the contact lens comprises a central zone displaced from a three dimensional geometric center of the contact lens to compensate for a deviation of the displaced apex of the cornea from a center of a pupil of the eye or a deviation of the displaced apex of the cornea from a line of sight of the eye.
2. The method of claim 1 , wherein the central zone has a substantially oval curvature and a substantially oval perimeter.
3. The method of claim 2 , wherein the central zone is rotationally asymmetrical having a first meridian with a semi-meridian shorter in radius than a corresponding semi-meridian of a second meridian.
4. The method of claim 1 , wherein the contact lens further comprises an intermediate transition zone formed integral with a periphery of the central zone.
5. The method of claim 4 , wherein the contact lens further comprises a peripheral zone formed integral with a periphery of the intermediate transition zone, wherein the peripheral zone terminates at a lens edge.
6. The method of claim 3 , wherein one semi-meridian is lower in eccentricity than the other semi-meridian.
7. The method of claim 3 , wherein the eccentricity of the semi-meridians are substantially equivalent.
8. The method of claim 3 , wherein the semi-meridians are unequal in eccentricity and have radii longer than a shortest semi-meridian.
9. The method of claim 4 , wherein at a junction of the central zone and the intermediate zone, sagittal height is circumferentially equivalent.
10. The method of claim 4 , wherein at a junction of the central zone and the intermediate zone, sagittal height has a prescribed deviation from equivalent sagittal height.
11. The method of claim 1 , wherein the anterior lens surface contains a correction for neutralizing low and higher order aberrations of a lens-eye system.
12. The method of claim 11 , wherein the correction for neutralizing low and higher order aberrations is calculated to produce a specific spherical aberration.
13. The method of claim 1 , wherein the anterior lens surface contains a bifocal correction.
14. The method of claim 1 , wherein the anterior lens surface contains a multifocal correction.
15. The method of claim 1 , wherein the contact lens comprises an encapsulated rigid lens for a bifocal or multifocal correction.
16. A method of fitting a contact lens for keratoconus, comprising:
determining a central keratometry measurement of a patient's eye;
measuring a horizontal iris diameter of the eye;
determining a sagittal height of a cornea of the eye from a cornea-sclera junction to an apex of the cornea using the central keratometry measurement and the horizontal visible iris diameter;
determining an amount of displacement of an apex of the cornea; and
determining a posterior curvature of the contact lens using the sagittal height, the central keratometry measurement, the horizontal visible iris diameter, and the displacement of the apex of the cornea;
wherein the contact lens comprises a central zone displaced from a three dimensional geometric center of the contact lens to compensate for a deviation of the displaced apex of the cornea from a center of a pupil of the eye or a deviation of the displaced apex of the cornea from a line of sight of the eye.
17. The method of claim 16 , further comprising determining a bifocal correction.
18. The method of claim 16 , further comprising determining a multifocal correction.
19. The method of claim 16 , further comprising determining a correction for neutralizing low and higher order aberrations, calculated to produce a specific spherical aberration.