PUPILLARY FUNCTION IN HUMAN AMBLYOPIA

Quantitative measurements of pupillary function (response amplitude an d latency) were made for normal eyes and for normal and fellow amblyop ic eyes of groups of strabismic and anisometropic amblyopes. Stimuli c onsisted of luminance modulation of a large, evenly lit area (pupil li ght reflex) as well as contrast modulation of sinusoidal gratings (pup il grating response) of fixed, space-averaged luminance. Measurements were made of the direct and the consensual reflex under monocular stim ulation. A comparison of the amplitude of the pupil light reflex as a function of luminance modulation showed no significant differences bet ween normal and fellow amblyopic eyes for both the strabismic and anis ometropic groups of amblyopes studied. A similar comparison of the ass ociated response latencies showed significant difference between norma l and fellow amblyopic eyes for both groups. In general, reductions in response amplitude and latency of the pupil grating response were fou nd in individuals from each group when comparing the good and the affe cted eyes, although the observed group differences were only significa nt in the strabismic group. Interestingly, statistically significant r eductions in both amplitude and latency for both the pupil light refle x and the pupil grating response were found between the eyes of normal observers and the so-called normal eyes of amblyopes in both groups s tudied. These results suggest that the type of pupillary deficit in am blyopia is a complicated one, depending not only on the type of amblyo pia (strabismic or anisometropic) and the type of stimulus employed (l ight or pattern), but also on the parameter assessed (amplitude or lat ency) and whether the amblyopic result is referenced to its fellow nor mal eye or to the normal eye of a non-amblyopic observer. Since the pu pil response to light flux changes is not mediated exclusively via the retinal projection to the midbrain and may also involve the activity of central visual pathways, the results obtained in this study cannot be used to provide definitive evidence for the site of abnormality in amblyopia.