Contrast is defined as the difference in luminance or brightness of contiguous objects and is mathematically derived by the formula (maximum luminance - minimum luminance) / (maximum luminance + minimum luminance). The inverse of a person's contrast threshold for an object or pattern of any size (the point at which it is first seen) is termed contrast sensitivity. Glare is defined as the sensation of luminance greater than that to which the eyes are adapted. Glare is most evident clinically in situations in which light scattering occurs (cataract, corneal edema).
These concepts, which impinge directly on visual function, have been described for over 50 years, have been oft ignored and poorly understood for much of that time, and today are receiving much attention in the ophthalmic literature. Their history and the current state of the art of visual function testing are covered in this text in a clear, concise manner by the editors