Scleral lenses are large diameter rigid gas permeable lenses that range from 14 mm to over 20 mm in diameter. They are termed “scleral” lenses because scleral lenses completely cover the cornea (the clear dome of tissue that covers the colored part of the eye) and extend onto the sclera (the white part of the eye that forms the outer wall of the eye).
As large diameter rigid gas permeable lens designs have developed, so have classification systems to describe these lenses. Many of these classification systems are based solely on lens size. However, these lenses could also be classified based upon their fitting characteristics: corneal lenses are supported exclusively by the cornea, and do not extend past the limbus (the junction between the cornea and the sclera). Corneoscleral lenses are supported by both cornea and sclera and extend past the limbus. Mini-scleral and scleral lenses, commonly referred to as scleral lenses, are supported exclusively by the sclera and completely vault the cornea and the limbus.
Large diameter scleral lenses offer certain advantages over corneal lenses. First, large-diameter lenses may be more comfortable than corneal lenses. The cornea is one of the most highly sensitive tissues in the body. The conjunctiva (soft, clear tissue that lies over the sclera) is much less sensitive than the cornea. Lenses that rest primarily or exclusively on the conjunctiva may induce less sensation than smaller lenses that rest upon the cornea. This is why scleral lenses are extremely comfortable.
In some patients, corneal tissue is damaged. Because scleral lenses do not touch the cornea, the cornea is bathed all day long with preservative free saline to rejuvenate the ocular surface. Scleral lenses extend under the upper and lower lids and rarely dislocate. Scleral lenses demonstrate excellent centration and stability.
Patients with irregular corneas, patients with conditions that affect the tear film, and patients with refractive error (nearsightedness, farsightedness, astigmatism and presbyopia) who are unable to wear other forms of correction could benefit from scleral lenses.
Conditions such as keratoconus and pellucid marginal corneal degeneration cause irregularity of the cornea. Surgery (keratoplasty, refractive surgery) can also lead to corneal irregularity. If the cornea is not smooth, vision will not be easily correctable with spectacles or most soft contact lenses. Scleral lenses mask this irregularity and allow for improved vision by providing a smooth front surface.
Some patients have disorders that affect the quality or quantity of tears that help to keep the eye’s surface smooth and healthy. Dry eye syndrome, graft vs. host disease, Sjögren’s syndrome, Stevens Johnson syndrome, and neurotrophic keratopathy are examples of such conditions. Some inflammatory conditions, including limbal stem cell deficiency and ocular cicatricial pemphigoid, also cause serious damage to the front surface of the eye. Patients who cannot close their lids completely may also experience problems with the health of the surface of the eye. The fluid reservoir beneath a scleral lens may improve comfort, and may allow the corneal surface to heal.
Patients who need visual correction, but are unable to wear other contact lenses, may find scleral lenses more comfortable than other lens designs.
You may benefit from scleral lenses if you have one of the following conditions:
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