Scleral lenses trap a reservoir of fluid behind the lens. This fluid protects the cornea and, in some cases, may allow it to heal.
Scleral lenses are large-diameter rigid gas permeable lenses. They can range from 14 mm to over 20 mm in diameter. 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).
For more information, see Scleral Lens Education Society. Note: the Scleral Lens Education Society is a non-profit largely operated and supported by optometrists and makers of scleral lenses, not patients.
Reference
What are scleral lenses?
Retrieved October 20, 2015.
The Scleral Lens Education Society
http://www.sclerallens.org/about