Differences in vernier discrimination for grating between strabismic and anisometropic amblyopes.

Two gratings composed of lines were displayed one above the other, and the vernier threshold was measured as a function of spatial frequency and vertical separation between gratings for 12 strabismic and/or anisometropic amblyopes. The vernier acuity of the anisometropic amblyopes was similar to that of nonamblyopic eyes when scaled proportionally to their reduced grating acuity. Strabismic amblyopes, on the other hand, have poorer vernier acuity than might be predicted from their grating resolution, even at low spatial frequencies. In addition, the strabismic amblyopes showed "crowding effects" for vernier gratings well within their resolution limit, while anisometropic amblyopes, like normals, showed no such effects.