Positional loss in strabismic amblyopia: inter-relationship of alignment threshold, bias, spatial scale and eccentricity

In order to understand the spatial loss in strabismic amblyopia and its relationship to the contrast sensitivity deficit, we measured alignment performance for a three element vertical alignment task in which the elements were equi-visible, spatial Gabors. We derived the threshold and bias and compared these for stimuli of different spatial scale and eccentricity. Our results suggest that: (1) the deficits for alignment thresholds and bias are uncorrelated; (2) in the majority of strabismic amblyopes, both deficits are scale invariant; (3) the form of the regional distribution depends on the spatial measure used and the scale at which it is measured; and (4) there is a poor correlation between the deficit for either spatial measure and the contrast sensitivity loss.