Gas-Permeable Lenses
Modern corneal Gas Permable (GP) lenses have been used as the gold standard treatment for keratoconus since the 1980s. There have been many well designed clinical studies that have shown the safety and efficacy of GP lenses used for improving vision with keratoconus, such as the Collaborative Longitudinal Evaluation of Keratoconus (CLEK). The CLEK study was a randomized, multi-centered, observational study that established that the safest way to fit a corneal GP lens is by clearing the apex of the cone, thereby reducing mechanical abrasion of the highest portion of the cornea. Poorly fitting GP lenses are correlated with increased risk for central corneal scarring. GP lenses have pros and cons associated with them:
Hybrid Lenses
Hybrid lenses are corneal contact lenses that have a central gas-permeable (GP) region, hyper-bonded to a skirt of soft lens material. There have been many generations of hybrid lenses since they were first introduced in the 1980s. Recent hybrid lens designs represent a huge leap forward for the treatment of keratoconus and other ectasias. New designs have materials, both soft and GP, that allow extreme amounts of oxygen to pass through to the cornea. The new generation lenses also have design features which are built specifically to accommodate the shape of a keratoconic eye. There are pros and cons associated with these lenses.
Scleral Lenses
Scleral lenses are very large diameter GP lenses that do not contact the cornea. Instead, their weight is distributed over a broad area on the relatively insensitive sclera, or white part of the eye. For this reason, they tend to be a very safe, effective, and comfortable means of vision correction for those with keratoconus. Scleral lenses have pros and cons associated with their wear:
Custom Scleral Lenses
There are currently five practices in the world who have access to truly customized scleral prosthetics. A customized scleral prosthetic is a process whereby a mold, similar to molds taken for orthodontics, is taken of the shape of the eye. The mold is sent to a laboratory who scans the mold and inputs the scan into a computer aided design (CAD). A scleral prosthetic is built from the CAD file and manufactured. This is the ultimate in scleral lens technology. For those who have failed with traditional sclerals or for whom traditional sclerals are not an option, this technology is sight saving. There are pros and cons with this technology:
Melanie Frogozo, OD