Contact Lens Prescription BY MARY JAMESON, BHS, COA, NCLC, CPOT
What do the numbers on a contact lens prescription mean? How do
they relate to a patient's eyes? How important are they? With
all of the controversy surrounding the issue of releasing
contact lens prescriptions, we should understand what every
detail of the prescription means. Measuring Base Curve The back
of a contact lens features a series of curves. These curves help
the contact lens fit the contour of a cornea. The main back
surface curve of a lens is the base curve. It represents the
central radius of curvature of the back of the lens. The base
curve corresponds to the keratometry reading, the measurement of
a patient's corneal curvature. We typically record keratometry
measurements in diopters of power and typically measure the base
curve reading in millimeters of radius. You can use a conversion
chart to transition from diopters to millimeters of radius. When
you select a trial lens, you can choose a base curve that is on
K (meaning it mat