Scleral lens
A scleral lens is a large lens that rests on the sclera and creates a tear-filled vault over the cornea. Scleral lenses are designed to treat a variety of eye conditions, many of which do not respond to other forms of treatment.
Design
Modern scleral lenses are made of a highly oxygen permeable polymer. They are unique in their design in that they fit onto and are supported by the sclera, the white portion of the eye. The cause of this unique positioning is usually relevant to a specific patient, whose cornea may be too sensitive to support the lens directly. In comparison to corneal contact lenses, scleral lenses bulge outward considerably more. The space between the cornea and the lens is filled with artificial tears. The liquid, which is contained in a thin elastic reservoir, conforms to the irregularities of the deformed cornea, allowing vision to be restored comfortably. This helps to give the patient BCVA, or Best Corrected Visual Acuity.
Uses
Therapeutic use
Scleral lenses may be used to improve vision and reduce pain and light sensitivity for people suffering from growing number of disorders or injuries to the eye, such as microphthalmia, keratoconus, corneal ectasia, Stevens–Johnson syndrome, Sjögren's syndrome, aniridia, neurotrophic keratitis (aneasthetic corneas), complications post-LASIK, complications post-corneal transplant and pellucid degeneration. Injuries to the eye such as surgical complications, distorted corneal implants, as well as chemical and burn injuries also may be treated by the use of scleral lenses.
Use in special effects
Special effect scleral lenses have also been used to produce eerie eye effects in films, such as the whited-out eyes of the monsters in Evil Dead, or blacked-out eyes in Underworld and Underworld: Evolution, or the Star Trek episode Where No Man Has Gone Before. These lenses tend to be uncomfortable and sometimes impede the actors' vision, but the visual effects produced can be striking. The lenses cost around $300, are custom-made to fit the wearer's eyes and can also be custom-painted, although most companies only sell lenses with a pre-designed look. There are many different designs available, from standard black lenses to flame-effect eyes, as well as a lens that makes the whole eye white. However, the wearer is unable to see anything while the latter variety of lens is worn. If looked after, the lenses can be kept for approximately one year. It is recommended that they be worn for a maximum of 5–6 hours at a time, and only occasionally.
Use for eye movement measurement
In experiments in ophtalmology or cognitive science, scleral lenses with embedded mirrors or with embedded magnetic field sensors in form of wire coils ("scleral coils") are commonly used for measuring eye movements.