Final answer:
Scleral contact lenses typically extend 1 to 2 millimeters beyond the limbus onto the sclera. They require a customized fitting due to variations in corneal and scleral shapes, which affect the magnification and visual quality. Proper fitting by eye care professionals is key due to the non-spherical nature of many corneas.
Step-by-step explanation:
Scleral contact lenses are designed to correct vision problems and are unique in that they are larger than regular contact lenses, extending onto the white part of the eye, or the sclera. These lenses vault over the cornea and rest on the sclera, typically extending 1 to 2 millimeters beyond the limbus, the border between the cornea and the sclera. This design allows them to be used for a variety of corneal issues and irregularities.
The fitting process for scleral lenses is complex due to the variations in the scleral shape, and it's important to ensure a proper fit to avoid complications. The radius of curvature of the cornea is a crucial factor considered during fitting because it affects the magnification and quality of vision provided by the lenses.
It is noted that a perfect fitting is often challenged by the non-spherical nature of many corneas, indicating the importance of a customized fitting process by a qualified eye care professional. These principles are also reflected in the context of eyeglass prescriptions, where power and placement relative to the eye (e.g., 1.50 cm for eyeglasses) play important roles in visual correction.