Abstract

The deviation of the fovea from the optical axis of the human eye is traditionally represented by the angle between the optical axis and the visual axis, the angle alpha. This angle is not only important in many fundamental measurements of the ocular constants and ocular aberrations, but also of great importance in clinical optometry.¹ We have developed a computer-controlled CCD video camera system of a high magnification and have measured the angles in a number of eyes both horizontally and vertically. Specially designed light sources, reference targets and precisely adjustable optical mounts enable the system to monitor and maintain the eye position within 0.03 mm. Due to possible transverse displacement and tilt of the crystalline lens, aligning all the Purkinje images was not possible for some subjects as reported by some earlier workers.^2,3 An approximate optical axis was then defined by aligning Purkinje images I and IV. The precision of the measurement is within 0.15 = B0. Repeatability of the measurement is found to be restricted mainly by the fixation error of the subject and is generally within 0.2 = B0. The angles we have obtained for the eight eyes ranges from +3.0 = B0 to +5.6=B0 horizontally, which is in the same direction but generally smaller than the values from Tschering’s measurement.2 However, the vertical values ranges from 0.5 = B0 to 1.5 = B0 with the visual axis downward which is opposite in sign to the value traditionally quoted. The angles for the two eyes of the same subject are within 1.1 = B0 horizontally and 0.6 = B0 vertically. Support of NSERC Canada is gratefully acknowledged.

© 1993 Optical Society of America