Preeti Verghese

Despite normal motor control, saccadic latencies are delayed in the non-preferred eye of patients with amblyopia ( approximately 25-100ms1,2). This delay extends to manual reaction time when responding to targets with the amblyopic eye ( approximately 50-100ms1,3,4). Previous researchers have shown a positive correlation between the delay and the magnitude of visual acuity impairment in the amblyopic eye5. This delay may be due to a difference in effective stimulus strength of the targets, since reaction times to weak stimuli are prolonged, decreasing as stimulus strength increases, until reaching a plateau6. Here, we measure saccadic and manual reaction times of normal and amblyopic subjects to the abrupt appearance of a Gabor patch at 5 degrees to the left or right of fixation, while varying the contrast of the patch. Even after adjusting for differences in effective stimulus strength, we find significant delays in both saccadic and manual response times when viewing with the amblyopic eye. We speculate that this irreducible delay may be a consequence of impaired ability to rapidly direct spatial attention with the amblyopic eye. 1 Mackensen, G. (1958). Reaktionszeitmessungen bei Amblyopia. Graefes Arch Ophthalmol 159:636 - 642. 2 Ciuffreda, K.J., Kenyon R.V. Stark L. (1978). Increased saccadic latencies in amblyopic eyes. Invest Ophthalmol Vis Sci 17: 697-702. 3 Von Noorden, G.K. (1961). Reaction time in normal and amblyopic eyes. Arch Ophthalmol 66:695-699. 4 Levi, D.M., Harwerth, R.S., and Manny, R.E. (1979). Suprathreshold spatial frequency detection and binocular interaction in strabismic and anisometropic amblyopia. Invest Ophthalmol Vis Sci 18:714-725. 5 Hamasaki, D.I. and Flynn, J.T. (1981). Amblyopic eyes have longer reaction times. Invest Ophthalmol Vis Sci 21:846-853. 6 Pieron, H. (1952). The Sensations: Their Functions, Processes and Mechanisms. London: Frederick Muller Ltd. Meeting abstract presented at VSS 2015.