ABSTRACT
The base curve of an ortho C lens is flatter than the curvature of the cornea by an amount expressed in diopters. It is equal to the total deviation of the myopic eye also measured in diopters. The assumption behind ortho K is that the curvature of the cornea would flatten by that amount before an object in the distance can come into focus, but ortho C is different from ortho K. An interesting phenomenon behind ortho C is that the improvement in vision is not due to a flatter cornea. It is an indication that the treatment involves resetting the correct neurological message to alter the curvature of the lens and eyeball. The design of an ortho C lens is almost the same as an ortho K lens. The main difference is in the thickness. To appreciate how altering just the thickness can correct a primary refractive error, the chapter examines the parts of the myopic eye that can deviate from the emmetropic eye.
