Symmetry detection in amblyopia

Purpose: It has been suggested that the term tarachopia, meaning ‘distorted sight’, provides an accurate description of the visual deficit in amblyopia. This follows psychophysical findings of spatial inaccuracy in amblyopia, as well as subjective reports of perceptual distortions by amblyopic observers. Mirror symmetry is a salient feature in normal human vision and its detection is critically dependent upon the spatial relations between the elements of the pattern. This study investigates whether the perceptual distortions in amblyopia extend to mirror symmetry detection. Methods: Three strabismic and three non‐strabismic amblyopes participated in the experiment (acuity range 6/9 to 6/90). Symmetric and random dot patterns were briefly presented (<250 msecs) at three retinal locations (centred at fixation, and 4° to the left and right of fixation). The patterns were generated and displayed on a Macintosh computer. After each stimulus presentation the subject was required to press one of two keys to indicate whether the pattern was symmetrical or random. The d ′ statistic was computed for three symmetry orientations (H, V, and 45°) for each of the three retinal locations. Results: Amblyopic‐eye performance was equivalent to fellow‐eye performance in 5 of the 6 amblyopes tested. In the remaining amblyope symmetry detection in the amblyopic eye. This is likely to have resulted from reduced visibility of the dot pattern since the acuity in this eye was 6/90. Conclusions: The ability to detect mirror symmetry in briefly presented dot patterns is not affected by amblyopia.