POSTERIOR PRINCIPAL PLANE OF THE OPTICAL SYSTEM OF THE EYE AND SIGNIFICANCE FOR REFRACTION

Refraction in the eye is determined by the position of the posterior focus of the eye in relation to the retina, which, in turn, depends on the length of axis and on the value of separate elements in the refractive apparatus of the eye, namely, radiuses of curvature of the cornea and of the surfaces of the lens, depth of the anterior chamber and thickness of the lens. The results of my investigations, described in a number of papers,1 have shown that the length of the axis, as well as the elements of the refractive apparatus, vary considerably and that this variability has a great, and sometimes decisive, significance for refraction, permitting one to evaluate properly a number of peculiarities associated with the anomalies of refraction. However, the length of axis and its significance for refraction are not the only factors determining refraction in the eye. The position of