Red-Green Glasses offer a functional advantage when used in vision testing and therapy. These wrap-around red/green glasses do not let in any side light, regardless of patient head or eye position. No white or ambient light interferes with the testing or therapy routines. Each eye receive maximum, proper color exposue. These red and green color lenses are designed to render proper hue and tint. Lenses are 100% accurate in the cancellation of Worth 4 Dot test, Three Character Test, most Lancaster Red/Green Tests, and Hess Screen Test colors. Western Optical's OS-943 Red Green Specs are supplied individually.