Psychophysical investigations of the temporal modulation sensitivity function in amblyopia: uniform field flicker

The temporal modulation sensitivity function was studied in eight strabismic and/or anisometropic amblyopes and in two subjects with amblyopia resulting from monocular stimulus deprivation (cataract and ptosis). Half of the strabismic/anisometropic amblyopes showed a reduction in the sensitivity of the amblyopic eye. These differences were more marked at low and middle temporal frequencies. Two strabismic/anisometropic observers showed little difference in sensitivity between the two eyes, but in the remaining two observers the amblyopic eye was slightly more sensitive to low-frequency modulation than was the nonamblyopic eye. Four of the strabismic/anisometropic amblyopes also showed a small (5% to 10%) but statistically significant difference in the critical fusion frequency, with the sensitivity of the amblyopic eye being reduced. These differences in sensitivity were not related to the visual acuity loss. However, all differences in sensitivity between the two eyes were reduced or eliminated when the mean luminance of the test field was decreased by 2 log units form 32 to 0.32 cd/m2, or with suprathreshold stimulation. One of the two stimulus-deprivation amblyopes showed a decrease in sensitivity to low and middle temporal modulation frequencies similar to that found in four of in sensitivity to low and middle temporal modulation frequencies similar to similar to that found in four of the strabismic/anisometropic amblyopes, and the other observer showed a marked decrease in sensitivity at all temporal frequencies. The losses in temporal resolution of the amblyopic eye in both strabismic/anisometropic and stimulus-deprivation amblyopia are small in comparison with those reported in the spatial domain.