Pupillary Escape and Visual Fatigue Phenomena in Optic Nerve Disease

Abstract

An afferent pupillary defect has been known as an important sign to detect abnormality of the optic nerve such as optic neuropathy. Clinically, light swing test is the most common method to detect the afferent pupillary defect. Recently, pupil cycle time (PCT) has been measured by using a stop watch under the standard slit lamp microscope [1]. When a small beam is focused on the pupillary margin, it provokes regular and persistent oscillation of the pupil. The PCT is the frequency of this oscillation converted in msec. Prolongation of PCT has been suggested in patients with retrobulbar optic neuritis (RBN) when measured under the slit lamp microscope [2]. Since the technique is relatively simple, we attempted to measure the PCT with RBN by using the same procedure. The results, however, differed according to the examiner, from patient to patient, and it was quite difficult to obtain a consistent PCT in a given patient. We have, therefore, recorded edge-light pupil oscillation by using a small slit of light projected by modifying streak retinoscope, and the pupil was observed by a sensitive infrared pupillometer [3]. The PCT was initially calculated by hand; thereafter, a digital computer with analogue to digital converter was used for calculting the PCT by Fourier analysis in normal people and in patients with RBN. The results indicated that there were no significant increases in the PCT in patients with optic neuropathy by both methods. On the other hand, pupil escape phenomenon was frequently seen during edge light pupillary oscillation in these patients [4].