While soft contact lenses have a much greater market share, corneal and scleral GP lenses remain important contact lens options. Scleral lenses have been gaining in popularity because of their benefits for dry eye therapy and irregular cornea management. But, there is a slowly growing resurgence of interest in corneal GPs—in part due to myopia progression management, but also because corneal GP lenses are being used to manage patients who have irregular corneas when reduced cost and ease of handling are desired.

If patients are not correctable to 20/20 with manifest refraction and have large amounts of refractive astigmatism, confirming the type of cornea is helpful in determining the lens design and parameters. With this in mind, let’s review the process of evaluating fluorescein patterns on four types of corneas fit with corneal GP lenses.

A Tale of Four Corneas

Exhibit 1: Significantly Toric Regular Cornea Figure 1 shows a spherical corneal GP lens on a cornea that has high regular astigmatism. The dark horizontal band indicates a with-the-rule pattern. A toric-back-surface corneal GP lens would improve lens centration and comfort.

Exhibit 2: Keratoconus Figure 2 shows a spherical corneal GP on a patient who has keratoconus. This patient also exhibits large amounts of corneal toricity, but unlike the previous patient, the cornea is irregular. Rather than a dark horizontal band, a small circular area represents the apex of the cone. This is a “three-point-touch” pattern.

Exhibit 3: Pellucid Marginal Degeneration (PMD) Figure 3 shows an 11mm spherical intralimbal corneal GP design on a patient who has PMD. PMD and keratoconus are both corneal ectasias, but PMD differs in that the location of protrusion is peripheral; when viewing the fluorescein pattern, the area of bearing is decentered inferiorly. Because the area of highest elevation is inferior in PMD, corneal GPs tend to decenter inferiorly, which requires a larger corneal GP lens.

Exhibit 4: Post-Radial Keratotomy (RK) Figure 4 shows an 11mm spherical intralimbal corneal GP design on a post-RK cornea. Fluorescein patterns for post-surgical corneas have varied areas of pooling and bearing that are unique from cornea to cornea. Because of the irregular topography, a larger-diameter lens can improve centration and allow for a larger optic zone.

Conclusion

Despite advances in computerized technology, fitting corneal GP lenses is still best performed by interpreting fluorescein patterns to determine the optimal parameters and fitting relationship. CLS