Contrast thresholds for sine gratings of children with amblyopia.

Contrast threshold functions were measured on 26 amblyopic children before and after minimal occlusion therapy. On initial presentation the relative contrast sensitivity deficit the amblyopic eye was in every case much less than that predicted from the deficit in visual acuity for letters. In fact, in seven of the children the contrast sensitivity functions for the amblyopic and fellow nonamblyopic eye were indistinguishable despite the expression of substantial amblyopia on letter charts. Only four children exhibited a substantial contrast sensitive loss in the amblyopic eye with a cut-off spatial frequency below 30 cycles/degree. The majority of children who showed deficits in contrast sensitivity did so only at medium and high spatial frequencies. On the basis of these findings it appears that measurements of contrast thresholds for single sinusoidal gratings do not probe fully the deficits of spatial resolution in amblyopia. Finally, among the few children who exhibited a sizeable initial deficit, only two showed obvious improvement in contrast sensitivity in response to minimal occlusion therapy.