Abstract: PURPOSE: Amblyopia is a developmental visual disorder that results from abnormal visual experiences during critical periods of development. It is believed that abnormal visual experiences disrupt the interocular connections in the visual cortex, resulting in impaired stereopsis in amblyopia. However, human visual system can extract depth information in space from various monocular cues, include perspective, shadows, blur, and texture etc. Whether the depth perception from the monocular cue is normal in amblyopia is not clear. On the other hand, the quality-of-life assessment of amblyopic patients is heavily based on their stereopsis function, while ignoring the abilities to processing other monocular depth cues. This might result in an underestimate of the quality of life for amblyopic patients. Thus, it is necessary to investigate the ability to extracting depth information from monocular cues in amblyopia. Given that texture cue is a representative monocular depth cue which generates significant depth perception, we attempt to investigate whether the depth perception of amblyopic monocular texture cue is normal.
METHODS: Twenty-three amblyopic patients (24.5 ± 4.0 years, 13 males), and eighteen normal participants with normal stereoscopic function and age-matched (24.4 ± 1.3 years, 8 males) were recruited. The amblyopic eye (AE), fellow eye (FE) of amblyopic patients, and the non-dominant eye (NDE) in normal participants were tested. In Exp 1, the slant stimuli textured with Voronoi pattern were used. The participants were asked to perform a discrimination task and a matching task. In the slant discrimination task, a 45° reference plane and a test plane were presented side-by-side on the display. The participants were required to indicate which of the two planes was rotated further away. The discrimination threshold was measured using a 3-up-1-down staircase procedure. In the slant matching task, the participants were required to adjust the angle of a straight line to match the angle of the slant they just saw. Five slant angles, 0°, 15°, 30°, 45°, and 60° were used. The trials of different angles were intermixed randomly. In Exp 2, same participants performed the discrimination and matching tasks with dihedral stimuli. The discrimination threshold and perceived angle for the dihedral stimuli were recorded.
RESULTS: In Exp 1, there were significant differences in the slant discrimination thresholds between the AE and NDE (t(39) = 2.161, P = 0.037, Cohen's d = 0.699) and between the AE and FE (t(18) = 2.987, P = 0.008, Cohen's d = 0.68). However, there was no significant difference in the perceived slant angle between the AE, NDE and FE (F(2,57) = 2.134, P = 0.128). No significant correlation was found between the discrimination threshold and visual acuity. In Exp 2, the discrimination threshold in the AE group was higher than that of the NDE (t(39) = 2.092, P = 0.043, Cohen’s d = 0.674), and than that of the FE (t(18) = 2.642, P = 0.017, Cohen’s d = 0.424). The threshold correlated significantly with visual acuity (r = 0.48, P = 0.019). However, there was no significant differences in the perceived dihedral angle between the AE, NDE and NE (F(2,57) = 0.06, P = 0.942).
CONCLUSIONS: In conclusion, the amblyopic patients showed normal ability to extract depth information from texture cue. This work provides a basis for future studies on monocular depth perception in amblyopia. It also suggests that the quality-of-life assessment should include the monocular depth perception.

Key words: Depth perception, Stereopsis, Amblyopia, Texture cue, Discrimination threshold