Note on the Focus of Concavo - Convex Lenses the Surfaces of which are of Equal Curvature

Extract

The ophthalmic surgeon has frequently to prescribe convex lenses of less than four inches focus for the correction of the optical defect in the eye left by removal of the intransparent crystalline lens in the operation for cataract. Occasionally, too, equally strong concave lenses are required to correct high degrees of short sight.