Contact Lenses for Keratoconus

Why glasses stop working

Glasses correct regular astigmatism, where the cornea is steeper in one meridian than another in a symmetric way. Keratoconus produces irregular astigmatism: a localized cone, usually below center, with steepening that varies from point to point. No spectacle lens can correct that, and vision with glasses becomes ghosted and smeared as the cone develops. A contact lens with a rigid front surface replaces the irregular cornea as the eye's optical surface, and the tear layer between fills the irregularity.

Lenses by stage

• Early: standard or custom soft toric lenses, sometimes with a thicker center to mask mild irregularity, while glasses still give acceptable vision
• Mild to moderate: rigid gas permeable lenses in keratoconus designs, which give excellent vision but can decenter and take adaptation; hybrid lenses with a vaulting rigid center and soft skirt for comfort and stability; or scleral lenses
• Moderate to advanced: scleral lenses, which vault the whole cornea, ignore the cone's shape, give stable vision and all day comfort, and protect a fragile surface
• After corneal transplant: almost always scleral lenses, fitted once the graft is stable

Piggyback fittings (a rigid lens over a soft carrier) are occasionally used for comfort in eyes that cannot be fitted otherwise.

Lenses and cross-linking

Cross-linking halts progression but does not sharpen vision, and most patients continue in lenses afterward. Rigid and scleral lenses come out for the procedure and for two to three weeks before any tomography, and are refitted once the cornea has stabilized, usually one to three months after treatment, because the corneal shape shifts slightly as it stiffens. The refit is from new maps.

The fitting

Corneal tomography maps the cone. A diagnostic lens is placed, its clearance over the cone is checked with fluorescein or imaging, and vision is measured. The custom lens is ordered and refined over one to three visits. Patients are taught insertion and removal, and follow-up checks the cornea under the lens. Keratoconus corneas are monitored alongside, and any change prompts both a scan and a lens check.

Do not rub

Eye rubbing is associated with progression of keratoconus, and lens wear can prompt it if the lens is uncomfortable or the eyes itch. A comfortable fit and treatment of allergy and dryness are part of protecting the cornea, not just a comfort issue.