Spatial tuning properties in human amblyopia cannot explain the loss of optotype acuity.

Strabismic amblyopes may exhibit in their squinting eye an almost normal contrast sensitivity to gratings although their optotype acuity is strongly impaired. This discrepancy cannot be accounted for by reduced selectivity of spatial-frequency channels or line-sensitivity functions. Alternative explanations for the loss of letter visual acuity as abnormal interactions between psycho-physical detector-mechanisms or defects in spatial phase sensitivity are discussed.