Contact lens masks to improve the visual image quality in best-corrected keratoconic eyes

Abnormalities or irregularities in the cornea, whether it is from scarring or an ectatic disease like keratoconus can significantly affect vision. Correcting such eyes with rigid gas-permeable (RGP) contact lenses can help regularize the cornea and improve vision. However, some aberrations persist despite wearing the best RGP contact lens correction.

This investigation looks into improving contact lenses by designing a customized mask on the contact lens plane. The image quality of keratoconic eyes can be improved by blocking light rays that stray too far from the best focus using a binary mask.

Corneal tomography and biometry data of 20 keratoconic SyntEyes were generated using a stochastic eye model and the best toric RGP contact lens corrections were calculated and applied to these eyes. Custom MATLAB software was used to perform ray tracing through the eye and determine ray coordinates on the retinal plane. Circular zones with radii of 0.015, 0.025, 0.05, and 0.1 mm were created on the image plane that acted as a virtual pinhole. Finally, masks in four regions were designed to block light rays that did not converge inside these virtual pinholes.

A region 4 mask significantly reduces the average root-mean-square wavefront error from 1.82 ± 0.50 to 0.32 ± 0.06 µm ( t test, p<0.05), while blocking 53.87 ± 4.68% of the incoming light. For masks of regions 3, 2, and 1, the root-mean-square wavefront error increases to 0.51 ± 0.01, 1.25 ± 0.36, and 1.81 ± 0.50 μm, respectively, and the amount of blocked light decreases to 30.35 ± 5.09, 8.49 ± 3.70, and 0.47 ± 0.63%, respectively.

Contact lens masks designed to filter out skewed light rays can increase the image quality in contact lens-corrected keratoconic eyes, but this must be balanced with minimal light loss.