Accurate clinical means of measuring intervisual axis distance.

Abstract

INCREASING emphasis is being placed on the proper positioning of the optical centers of ophthalmic lenses (trial case, refractor, or spectacle) with relation to the visual axes. Recognition is not generally given to the inaccuracies inherent in Viktorin's method, commonly used to measure the so-called interpupillary distance (P. D.). Furthermore, this method of P. D. measurement, even when performed accurately, does not determine the location of the visual axis upon which the optical center of the lens should be placed. Ideally, the distance between optical centers of lenses (termed O. C. D.) should correspond to the intervisual axis distance, or interocular distance, 1 abbreviated I. O. D., a term recently suggested to supplant the less accurate term interpupillary distance. Viktorin's method of measuring P. D.'s is illustrated in Figure 1. A few of the inaccuracies of this method of measurement may be noted: The observer's P.D. should be the same