Hyperacuity thresholds for oscillatory movement are abnormal in strabismic and anisometropic amblyopes

The hyperacuity performance of amblyopic individuals is known to be abnormal, particularly on vernier tasks. Oscillatory movement displacement thresholds (OMDT's) a form of hyperacuity, were investigated over a range of temporal frequencies (1, 4, 7, 10, and 13 Hz) in 8 normal controls, 5 strabismic amblyopes, and 4 anisometropic amblyopes to see if this form of hyperacuity was also affected by amblyopia. OMDT's were found to be significantly raised in all of the strabismic amblyopes and three of the four anisometropes over all temporal frequencies investigated when compared to the control group. In the fourth anisometrope, OMDT's were raised at low temporal frequencies only. The findings are interpreted as evidence that magnocellular and parvocellular channels are affected in the amblyopic visual system. The functional loss in amblyopia cannot be described completely unless both temporal and spatial thresholds are investigated.