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E. P. Herlihy, S. M. Archer; The Pupil in Suppression and Amblyopia. Invest. Ophthalmol. Vis. Sci. 2009;50(13):4700.
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To test the hypothesis that the apparent afferent pupillary defect that has been reported in amblyopic eyes is due to lack of fixation by the eye with poorer vision, and to determine if there is a magnitude of pupillary asymmetry that cannot be attributed to lack of fixation in amblyopia.
Ten volunteers with equal best corrected visual acuity in each eye and a normal eye exam were recruited. A twenty prism diopter base down prism was placed over the right eye, and the subject was instructed to fixate on a distant target and suppress the displaced image. Pupillary reactions were assessed with the swinging flashlight test. Asymmetric responses were quantified using neutral density filters.
Asymmetric pupillary responses were observed in seven of the ten subjects (70%) with equal visual acuity and normal eye exams when the subjects were instructed to maintain fixation with the eye without the prism [video clip]. Pupillary reactions equalized with a 0.3 log unit neutral density filter held over the eye without the prism in six of the seven subjects (86%). The pupillary asymmetry reversed in one of the seven subjects (14%) with the 0.3 log unit filter.
Lack of fixation caused an apparent afferent papillary defect in seven of ten normal subjects without amblyopia. Thus, there is no need to postulate a failure of development of retinal ganglion cells in amblyopes. However, no pupillary asymmetry resulting from lack of fixation measured greater than 0.3 log units in our study. Any larger asymmetric response warrants further investigation for optic nerve disease.
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