Abstract
Abstract: :
Purpose: Detection of radial deformation involves both contour integration and shape discrimination mechanisms. This study examines deficits in these mechanisms in strabismic, anisometropic and deprivation amblyopia. Methods: Subjects were patients with strabismic (n=15, VA ≤0.5 logMAR), anisometropic (n=11, VA ≤0.5 logMAR) or deprivation (n=6, VA ≷0.3 logMAR) amblyopia. Stimuli were paired circular D4 contours. The task was to identify the deformed circle in a spatial 2AFC staircase paradigm. Deformation threshold (log sec) was analysed as a function of contour frequency (CF), defined as radial cycles/contour length in viewing angle (log cyc/cl-deg). Based on Jeffrey et al (ARVO 2001) a bilinear model of the shape discrimination and contour integration mechanisms was fit to deformation threshold as a function of CF. The slope of the shape discrimination mechanism was set to -1 and the contour integration mechanism plateau to 0. The intersection point between the mechanisms c, and the vertical position of the plateau a were fit by the model. Results: Compared to control eyes (c=0.28 log cyc/cl-deg, a=0.90 log sec) the strabismic group had a decrease in c of 0.3 log cyc/cl-deg; at CF ≷c threshold was elevated by an average of 0.35 log sec while at CF<c there was no threshold deficit. The anisometropic group showed no change in c; but for CF≷c and CF<c, threshold was elevated by an average of 0.20 log sec. Those with deprivation amblyopia had a reduction in c ranging from 0.4 to 0.9 log cyc/cl-deg with the amplitude of reduction related to severity of amblyopia. All patients with deprivation amblyopia showed a threshold elevation for CF≷c (up to 1.27 log sec), in addition the 2 patients with severe amblyopia showed a threshold elevation for CF<c (0.34 log sec). Conclusion: The shift observed in c in the strabismic group is consistent with a shift in spatial scale of the contour integration mechanism. A uniform elevation in deformation threshold was observed in the anisometropic group, which is consistent with an efficiency loss affecting the threshold of both mechanisms. The pattern of threshold elevation in moderate deprivation amblyopia was similar to strabismic amblyopia but both changes in spatial scale and efficiency were apparent in severe deprivation amblyopia.
Keywords: 313 amblyopia • 586 spatial vision • 588 strabismus