Edge-light pupil oscillation of optic neuritis

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Abstract
Edge-light pupil oscillations induced by a thin slit of light projected from a streak retinoscope and focused on the pupillary margin were recorded by an infrared television pupillometer. The oscillation period expressed as pupil cycle time (PCT) was calculated by hand from the recorded chart and by means of a digital computer with an analogue to digital converter in selected cases. In these cases, Fourier analysis was also undertaken. Forty patients with optic neuritis and 60 normal subjects, matched for age. were examined. The mean value and standard deviation of the PCT obtained by hand analysis of the pupil oscillation were 851±70 msec in the affected eyes of patients with optic neuritis and 834±65 msec among the controls. By computer analysis. the PCT in the affected eyes of patients with optic neuritis was 892±89 msec, while the value obtained for the controls was 890±64 msec. There were no statistical differences between patients and controls in either method. However, in patients with optic neuritis, the amplitude of the edge-light pupil oscillations tended to gradually diminish with time as the light was held on the eye: until it stopped cycling regularly. This pupillary behavior, which was never observed in normal subjects, was frequently seen in patients with optic neuritis if the visual acuity was less than 1.0. Therefore. this was considered to be a characteristic pattern among these patients. This was hard to observe under a slit lamp microscope. Therefore, recording of the pupil movements by a sensitive pupillometer is necessary for diagnosis of optic neuritis. Furthermore, Fourier analysis of the oscillation may be valuable for accurate determination of the Pupil Cycle Time.

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