Custom Contact Lenses
A normal cornea is generally steepest near its geometric center; beyond the center, the surface flattens. The steep area is known as the apical zone, and its center is the corneal apex. Outside the apical zone, which is approximately 3–4 mm in diameter, the rate of peripheral flattening may vary significantly in the different corneal meridians. This variation is important, because peripheral corneal topography significantly affects the position, blink-induced excursion patterns, and, therefore, wearing comfort of corneal contact lenses, especially gas-permeable lenses.
The availability of corneal topography and wavefront aberrometers, together with desktop graphics programs and computerized lathes, enables the preparation of individually tailored contact lenses that assist with otherwise difficult fits, such as keratoconus, trauma, and transplant. There is interest in the attempt to design lenses in this way to optimize wavefront correction for normal corneas, with the caveat that contact lenses constantly change their position on the cornea. Specially painted lenses, another custom service, are provided to reduce glare in aniridia and albinism by providing a pupil.
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.