Revival of the Scleral Contact Lens
The concept of a scleral lens is to optically neutralize the cornea with a lens-enclosed liquid reservoir. Although at one point it was an underutilized ophthalmic tool, these lenses are gaining popularity in the Netherlands for the treatment of postkeratoplasty astigmatism, keratoconus, and other forms of corneal ectasia. The large size of the lens creates a sclera-bearing surface and retains a precorneal fluid reservoir providing optical neutralization of an astigmatic or irregular corneal surface (Figure 1).
HISTORY OF THE LENS
Don Ezekiel, OD, of Australia, first reported using the gas-permeable scleral lens in 1983.1 Five years later, Kenneth W. Pullum, FCOptom, DipCLP, of Innovative Sclerals, Ltd. (Hertford, UK), developed gas-permeable scleral lenses made from impressions of the eye.2 Later, Polymer Technology Corp. (Rochester, New York) developed Itafluorfocon B, DK 127x10-11 units, (ie, the raw material used to produce scleral lenses).3 This breakthrough, along with the lathe Optoform 80 (Precitech, Keene, New Hampshire)—a lens design software program based on mathematical spline functions for defining and creating junctionless surface shapes—allowed contact lens laboratories to produce their own scleral lenses. With the inflation of scleral lens designs, those optometrists familiar with lens fitting started increasing their use of the scleral lens.
The gas-permeable scleral lens is a stable lens with a large optic zone that rests on the sclera and vaults over the cornea. The lens has minimal interaction with the eyelids because of its large diameter. The size as well as high oxygen permeability stabilize the fit of the lens and make it an ideal choice for corneal protection.
A trial of 28 nonventilated rigid gas-permeable lenses with variation in scleral zone radius (range, 13-14.5 mm) and an overall diameter of 18 to 24 mm, revealed that adapting the design of the haptic-bearing surface of the device to the eye-specific topography is an empirical process. It is the cornerstone of the fitting process. Patients outside the normal corneal profiles (eg, 0.8- and 2-mm forward projection from the virtual sclera) were fitted with the lens.
Primary indications for the scleral lens included keratoconus or other forms of corneal ectasia (70%), postkeratoplasty astigmatism (15%), and ocular surface irregularities (10%). Wearing time, which varied between 3 and 18 hours per day for 91% of patients, also differed from day to day. Within the first 6 months, 9% of eyes with suspended lenses had discontinued wear or failed a trial of a scleral lens in their fellow eye.
MANAGING THE FITTING PROCEDURE
From the aforementioned study, we have gathered that a glove fit on the sclera is not essential, but the scleral zone needs to be sufficiently sealed to prevent the introduction of air bubbles. Additionally, one must be aware that the optic zone projection (OZP) (ie, the distance between the corneal epithelium and the virtual scleral radius) may vary from 1.60 to 3.12 mm in progressive increments of half-corneal thickness. Increasing the OZP reduces corneal contact, while decreasing OZP reduces excessive clearance.
We found that an apical clearance of between 0.2 and 0.3 mm is a satisfactory target range for a nonventilated scleral lens. Although it is not critical to find the exact measurement of corneal clearance, excessive OZP does make it more difficult to maintain an air-free precorneal fluid reservoir (Figure 2). Furthermore, insufficient clearance could create corneal contact zones, which often reduce comfort and tolerance of the lens.
From this study, we concluded that scleral lenses play a significant role in the management of corneal abnormalities, especially in patients with corneal ectasia, post-corneal transplant, or ocular surface disease.
Fred A.G.J. Eggink, OD, PhD, is an optometrist at the Academic Hospital Maastricht, in the Netherlands. Dr. Eggink states that he has no financial interest in the products or companies mentioned. He may be reached at fredeggink@hotmail.com.
Rudy M.M.A. Nuijts, MD, PhD, is Associate Professor of Ophthalmology at the Department of Ophthalmology at Academic Hospital Maastricht, in the Netherlands. He states that he has no financial interest in the products or companies mentioned. Dr. Nuijts may be reached at rnu@compaqnet.nl.
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