Fig. 8. A. Contrast sensitivity functions for the normal (open circles) and amblyopic (closed circles) eyes of a patient with strabismic amblyopia. The difference between the eyes is plotted in the upper part of the figure and is significant only at high spatial frequencies. B. Contrast sensitivity functions for a different strabismic amblyopic patient. In this case, the eyes differ significantly at all spatial frequencies. The grating acuity of the amblyopic eyes is the same in the two cases. (Hess RF, Howell ER. The threshold contrast sensitivity function in strabismic amblyopia: Evidence for a two-type classification. Vis Res 1977;1049, 1051.)