Border enhancement as an index of contact lens performance.

In simultaneous border contrast enhancement, a border formed by an abrupt luminance discontinuity is perceptually enhanced on the bright side by a band of greater brightness and on the dark side by a band of greater darkness. The width of these perceived bands is very sensitive to small changes in the retinal image quality. This study explored the effect of contact lenses of varying steepness on the border enhancement spread. It was found that, over time, the effect of a contact lens on this spread generates a characteristic function. Furthermore, certain features of this function reflect the degree of steepness of the contact lens. It is suggested that the most important factors determining this function are tear flow and scatter-producing corneal edema.