Gas-Permeable Scleral Contact Lenses
A scleral lens has a central optic that vaults over the cornea and a peripheral haptic that rests on the scleral surface (Fig 5-15). The shape of the posterior optic surface is chosen to minimize the volume of the fluid compartment while avoiding corneal contact. The posterior haptic surface is configured to minimize localized scleral compression; the transitional zone that joins the optic and haptic surfaces is designed to vault over the limbus.
Figure 5-15 Scleral contact lens.
(Redrawn with permission from Albert DM, Jakobiec FA, eds. Principles and Practice of Ophthalmology. Philadelphia: Saunders; 1994;5:3643. Redrawn by Christine Gralapp and modification redeveloped by Leon Strauss, MD, PhD.)
These RGP lenses, with or without channels, must vent tears in and out to prevent buildup of suction onto the cornea and allow ample circulation of fresh tears beneath the lens. Improved RGP chemistry has enabled these lenses to be well tolerated. They have 2 primary indications: (1) correcting abnormal regular and irregular astigmatism in eyes that cannot be fit with corneal contact lenses, and (2) managing ocular surface diseases that benefit from the constant presence of a protective, lubricating layer of oxygenated tears, such as pellucid degeneration, Terrien marginal degeneration, keratoconus, Ehlers–Danlos syndrome, elevated corneal scars, and astigmatism following penetrating keratoplasty. These lenses can be helpful with complications of Stevens–Johnson syndrome, graft-vs-host disease, tear layer disorders, and ocular cicatricial pemphigoid, protecting the fragile epithelium of these corneas from the abrasive effects of keratinized eyelid margins associated with distichiasis and trichiasis and from exposure to air. They have promoted the healing of some persistent epithelial defects, where other strategies have been unsuccessful. Semi-scleral lenses, extending not as far onto the sclera, have diameters 15–18 mm; scleral lenses have larger diameters, 18.1–24 mm.
Excerpted from BCSC 2020-2021 series : Section 3 - Clinical Optics. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.