What Are Scleral Lenses?
Scleral contact lenses are large-diameter rigid gas permeable lenses that vault entirely over the cornea and land on the sclera (the white part of the eye). Unlike standard GP lenses that rest on the cornea, scleral lenses create a fluid-filled space between the back surface of the lens and the front surface of the cornea, providing unique therapeutic and optical advantages.
Scleral lenses have transformed the management of irregular corneas and severe ocular surface disease, offering clear vision and comfort to patients who cannot succeed with other contact lens modalities.
Design Principles
Corneal Vault
The central zone of a scleral lens is designed to completely clear the cornea without touching it. This vault provides:
- Protection of the corneal epithelium from mechanical contact
- A smooth optical surface independent of corneal irregularity
- Space for a fluid reservoir that hydrates the corneal surface continuously
Fluid Reservoir
Before insertion, the bowl of the scleral lens is filled with preservative-free saline. This fluid:
- Continuously bathes the corneal surface throughout wearing time
- Fills in corneal irregularities, creating a smooth refractive surface
- Provides constant hydration for patients with severe dry eye
- Acts as a liquid bandage for compromised corneal surfaces
Scleral Landing Zone
The peripheral zone of the lens rests on the sclera and conjunctiva:
- The sclera is less sensitive than the cornea, contributing to comfort
- The landing zone must align with the scleral curvature to distribute pressure evenly
- Poor alignment causes discomfort, conjunctival blanching, or lens rocking
The defining feature of a scleral lens is that it vaults completely over the cornea and rests on the sclera. This corneal clearance is what distinguishes sclerals from corneal GP lenses and is the source of their therapeutic advantages for irregular corneas and dry eye.
Size Classification
Large-diameter lenses are classified by overall diameter:
- Corneo-scleral lenses: 12.5-15 mm. Rest partly on the cornea and partly on the sclera
- Mini-scleral lenses: 15-18 mm. Vault the cornea but have a smaller scleral landing zone
- Full scleral lenses: 18-24 mm. Maximum vault and stability with the widest scleral landing zone
Clinical Indications
Irregular Corneas
- Keratoconus: The fluid reservoir masks corneal irregularity, providing vision superior to glasses or soft lenses
- Pellucid marginal degeneration: Similar irregular astigmatism management
- Post-surgical irregularity: After corneal transplant, radial keratotomy, or LASIK complications
- Corneal scarring: The fluid fills in surface irregularities caused by scarring
Severe Dry Eye and Ocular Surface Disease
- Sjogren's syndrome: Continuous hydration from the fluid reservoir
- Stevens-Johnson syndrome: Corneal protection and hydration
- Graft-versus-host disease: Severe dry eye management
- Neurotrophic keratopathy: Protection of an insensitive cornea
Other Applications
- High or irregular astigmatism not correctable with soft toric lenses
- Prosthetic use: Cosmetic improvement of disfigured eyes with custom tinting
Fitting Considerations
- Vault assessment: Use optical coherence tomography (OCT) or slit lamp with optic section to measure central clearance. Adequate vault at insertion (typically 200-400 microns) will settle during wear
- Avoid corneal touch: Any area where the lens contacts the cornea can cause epithelial damage and must be corrected
- Scleral alignment: The landing zone should show even blanching without excessive pressure or edge lift
- Bubble management: Air bubbles trapped under the lens during insertion must be removed, as they cause corneal desiccation in the affected area
Inserting a scleral lens without completely filling the bowl with saline. Trapped air bubbles cause localized corneal drying and staining directly under the bubble. Patients must learn the proper insertion technique with the head tilted forward and the lens bowl completely filled.
For patients new to scleral lenses, a plunger (suction cup) insertion and removal system simplifies handling. The large lens diameter makes finger placement difficult for some patients, and the plunger provides controlled, centered placement.
Key Takeaways
- Scleral lenses vault completely over the cornea and rest on the sclera
- The fluid reservoir provides continuous corneal hydration and masks surface irregularities
- Primary indications include keratoconus, post-surgical irregularity, and severe dry eye
- Sizes range from corneo-scleral (12.5-15 mm) to full scleral (18-24 mm)
- Fitting requires assessment of vault clearance, scleral alignment, and absence of corneal touch
- Air bubbles must be avoided during insertion to prevent localized corneal desiccation