CLINICAL REFRACTION IN 3-DIMENSIONAL DIOPTRIC SPACE REVISITED

The traditional clinical designation of spherocylindrical power unambi guously specifies the refractive properties of a thin lens or refracti ve surface. This representation of dioptric power is not, however, opt imum in mathematical terms, as is apparent when, for example, two sphe rocylindrical lens powers are added. Alternative systems have been des cribed which are not subject to this same type of difficulty, and the essential feature of these other systems is that spherocylindrical pow er is defined in terms of a three-dimensional dioptric space in which the axes are usually orthogonal. The advantages of this orthogonality can be exploited in the practice of clinical refraction, provided lens powers in these three dimensions can be physically implemented. Syste ms using these characteristics have been introduced in the past, but t he clinical community has not adopted them on a widespread basis. Howe ver, systems which take advantages of these features do have unique ad vantages relative to traditional clinical refraction procedures. These characteristics, and refractive procedures which exploit their advant ages, are described.