Spectacle lenses are practical compromises between incompatible ideals. Lens strength, eye movements, pencils of rays to be focussed and position of work must all be considered. Plano lenses, with convex side from the eye or concave side toward it, are much nearer the ideal than the biconvex and biconcave commonly found in trial cases. They are most serviceable for testing spectacles by neutralization being applicable to all forms. Read before the American Ophthalmological Society, May, 1926. Spectacle lenses are practical compromises between incompatible ideals. Lens strength, eye movements, pencils of rays to be focussed and position of work must all be considered. Plano lenses, with convex side from the eye or concave side toward it, are much nearer the ideal than the biconvex and biconcave commonly found in trial cases. They are most serviceable for testing spectacles by neutralization being applicable to all forms. Read before the American Ophthalmological Society, May, 1926.