Aspheric Contact Lenses
Thursday, December 18th, 2008The cornea of the eye should be spherical on the outer surface. If you took a round ball, and sliced off about one eight off the end, you would be left with roughly the shape of a cornea. Regular contact lenses are spherically shaped both on the inside and outside surfaces near the cornea of the eye. Subtle conditions can cause the cornea to lose its spherical shape, which in turn may cause blurred vision, and a not so subtle symptom.
Astigmatism of the cornea is one condition where blurriness results. Astigmatism is a condition where the cornea loses its spherical shape and is elongated on one axis. Presbyopia is an age related problem. As we get older, the shape of the eye (among other things) changes shape. When the surface of our eyes change shape, we begin to struggle in certain conditions. For the most if you have Presbyopia, you will have difficulty focusing on items close up. Aspheric contact lenses are designed to help with these conditions.
In Rosenbloom & Morgan’s Vision and Aging (By Alfred A. Rosenbloom, Meredith W. Morgan, P 233) aspheric contact lenses are described as lenses without inside curvature near the center of the lens. The inside surface is instead flattened and progresses at an angle, so aspheric lenses may also be used for progressive lens functions, a common requirement for people with presbyopia who wish to wear contact lenses.
Two well known aspheric contact lenses are Frequency 55 Aspheric and Biomedics 55 Premier. “55” refers to the amount of water content in these contact lenses. Water is one medium used to circulate oxygen around surface of the eye. Oxygen circulation is improved by using silicon hydrogel lenses, which may be worn for longer periods of time.