Scleral lenses are large-diameter lenses, about the same size as most soft contact lenses. They are called “scleral” lenses because they 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).
Corneal lenses sit on the cornea and do not extend past the junction between the cornea and the sclera. Scleral lenses are supported exclusively by the sclera, and completely vault (don’t touch) the cornea and the limbus.
Soft lenses simply sit on the eye and therefore take the shape of the cornea. Distortions in the cornea such as astigmatism or imperfections after LASIK, PRK, or other refractive conditions, therefore come through, and sometimes don’t achieve the clarity that most people are looking for. Soft lenses often dry out and therefore cause blurred vision, feelings of dryness and irritation, especially when people work on computers or read extensively.
Why are scleral lenses useful?
Scleral lenses offer certain advantages.
- These lenses are approximately the same size as most soft contact lenses.
- These lenses rest primarily on the white part of the eye (sclera and conjunctiva) and are usually more comfortable than lenses than lenses that rest on the cornea.
- They are ideal for patients that have a dry or a very wet eye because they trap a reservoir of fluid behind the lens. This then protects the cornea, and may even allow it to heal in cases where the cornea was damaged.
- These lenses extend under the upper and lower lids are rarely dislocate.
Who could potentially benefit from scleral lenses?
- Patients with irregular corneas
- Patients with conditions that affect the tear film
- Patients with refractive error (nearsightedness, farsightedness, or astigmatism) 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 in the surface of the eye.
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 clearer vision by providing a smooth front surface through which light can enter the eye.
Some patients have disorders that affect the quality or quantity of tears that help to keep the eye’s surface smooth and healthy. Examples include: Dry eye syndrome, graft vs. host disease, Sjogren’s syndrome, Stevens Johnson syndrome, and neurotrophic keratopathy are examples of such conditions.
Some inflammatory conditions 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 trapped beneath a scleral lens may improve comfort for these patients, and may allow the corneal surface to heal.
Patients who need visual correction, but are unable to wear other contact lenses, may find larger-diameter lenses more comfortable than other lens designs.
Are scleral lenses new?
Scleral lenses were actually the first contact lenses described in medical literature in the late 1800’s. However, due to manufacturing challenges and because of the lack of oxygen transmission through early lenses, scleral lenses did not become popular at that time. During the course of the next century, corneal rigid gas permeable lenses and soft contact lenses became increasingly popular.
But corneal rigid gas permeable lenses and hydrogel lenses couldn’t help to solve some of the problems caused by corneal irregularity and eye surface disease. In the 1980’s, scleral lenses made of rigid gas permeable materials began to be used in the treatment and management of conditions that could not be helped with other lens designs. “Breathable” materials minimize problems caused by lack of oxygen to the cornea, and better designs and manufacturing processes have made it easier to fit and prescribe scleral lenses.