Contact lens and methods of manufacture and fitting such lenses and computer program product
The invention is directed to a contact lens design and methods of manufacturing, fitting and using such lenses. The contact lens may be designed for use in a corneal refractive therapy (CRT) program. The lens provides a design which allows proper fitting of a patient, whether for corrective contact lenses or for a CRT program. Due to the rational design of the lenses according to the present invention, a minimal number of lens parameter increments can be identified to cover the range of common corneas. It is therefore possible to provide pre-formed lens buttons or blanks which are easily formed into a final design, thereby simplifying and speeding up the treatment process. Further, any adjustment of the lens design which may be required based upon trial fitting or the like, is easily envisioned and implemented by the fitter.
1. A method of fitting a contact lens, the contact lens having a central zone with a posterior surface having a curvature corresponding in a predetermined manner to the cornea of a wearer, at least one annular peripheral zone and an annular connecting zone, wherein the characteristics of the lens are selectively modifiable by varying at least one parameter selected from the group consisting of selectively changing the axial length of the connecting zone to produce directly corresponding changes in the sagittal depth of said contact lens,
selectively changing the volume distribution of a void space formed beneath the connecting zone by selectively changing the diameter of the central zone, the axial length of the connecting zone and/or the radial width of the connecting zone without otherwise affecting the fit of the lens,
selectively changing the radial location of possible peripheral tangential contact of said at least one peripheral zone to the peripheral cornea are provided by changing the angle made by the peripheral zone to the central axis of the lens, and selectively changing the edge lift of said contact lens from the cornea of a wearer are provided by changing the extension of the lens beyond the point of peripheral tangential contact of the lens with the cornea of a wearer or combinations thereof.
2. A method of fitting as set forth in claim 1 , wherein a lens set is provided having the central zone diameter, connecting zone width, lens diameter and edge profile provided with predetermined shapes, and measuring the preferred corneal curvature needed to eliminate refractive error for a patient, measuring central corneal curvature of the patient's cornea, and determining the additional parameters of connecting zone depth and peripheral zone angle from fitting or computer modeling to provide a contact lens to reshape the cornea in a desired manner.
3. A method according to claim 2 where the parameters of connecting zone depth and peripheral zone angle are derived by fitting lenses on the cornea of a patient from one or more fitting sets selected from the group of fitting lenses having a fixed base curve and a fixed peripheral zone angle with a series of connecting zone depths, having a fixed connecting zone depth and a fixed peripheral zone angle and a series of base curves, having a fixed connecting zone depth and a fixed base curve with a series of peripheral zone angles, or sets of these three types contain one or more lenses that are marked with a plurality of visible concentric rings.
4. A method of fitting as set forth in claim 1 , wherein the contact lens in fitted to alter the shape of a patients cornea comprising the steps of:
determining the desired corrected shape of a cornea,
imparting force to said cornea to alter its shape by means of said contact lens, central zone with a posterior surface curvature corresponding to said desired corrected shape,
wherein said annular peripheral zone is positioned relative to said cornea and shaped such that upon redistribution of corneal tissue by said central zone, said annular peripheral zone will contact said cornea, thereby acting to neutralize forces imparted on said cornea by said central zone.