Reynaud Alexandre, Hess Robert F
McGill Vision Research, Department of Ophthalmology, McGill University, Montreal, Québec, Canada.
Invest Ophthalmol Vis Sci. 2016 Oct 1;57(13):5107-5115. doi: 10.1167/iovs.16-19682.
Amblyopic patients have a deficit in visual acuity and contrast sensitivity in their amblyopic eye as well as suppression of the amblyopic eye input under binocular viewing conditions. In this study we wanted to assess the origin of the amblyopic suppression by studying the contrast perception of the amblyopic eye at suprathreshold levels under binocular and monocular viewing.
Using a suprathreshold contrast matching task in which the reference and target stimuli were presented to different eyes either simultaneously or successively, we measured interocular contrast matching in 10 controls and 11 amblyopes (mean age 35 ± 15; 5 strabismics; 3 anisometropes; 3 mixed). This was then used as an index of the binocular balance across spatial frequency and compared against the contrast sensitivity ratio measured with the same stimuli.
We observed that binocular matching becomes more imbalanced at high spatial frequency for amblyopes, compared with controls; that this imbalance did not depend in either group on whether the stimuli were presented simultaneously or successively; and that for both modes of presentation the matching balance correlates well with the interocular contrast sensitivity ratio (mean correlation coefficient of the slopes R = 0.7125).
The results from our amblyopes show comparable losses of contrast perception at and above threshold under these binocular viewing conditions across a wide spatial frequency range, much stronger than that observed for our controls. This occurs under conditions in which there should be no dichoptic masking. Furthermore, the matching contrast could be well predicted by the monocular contrast sensitivity. Altogether, this suggests that amblyopic suppression cannot be explained by normal dichoptic masking but rather an attenuation of the input.
弱视患者的弱视眼存在视力和对比敏感度缺陷，且在双眼视觉条件下会抑制弱视眼的输入。在本研究中，我们希望通过研究弱视眼在双眼和单眼视觉下超阈值水平的对比感知，来评估弱视抑制的起源。
使用超阈值对比匹配任务，其中参考刺激和目标刺激同时或相继呈现给不同的眼睛，我们测量了10名对照者和11名弱视患者（平均年龄35±15岁；5名斜视患者；3名屈光参差患者；3名混合性患者）的双眼对比匹配。然后将其用作跨空间频率的双眼平衡指标，并与用相同刺激测量的对比敏感度比值进行比较。
我们观察到，与对照者相比，弱视患者在高空间频率下双眼匹配变得更加不平衡；这种不平衡在两组中均不取决于刺激是同时还是相继呈现；并且对于两种呈现方式，匹配平衡与双眼对比敏感度比值都有很好的相关性（斜率的平均相关系数R = 0.7125）。
我们的弱视患者结果表明，在这些双眼视觉条件下，在很宽的空间频率范围内，阈值及以上的对比感知损失相当，比我们的对照者观察到的要强得多。这发生在不应存在双眼视差掩蔽的条件下。此外，匹配对比度可以通过单眼对比敏感度很好地预测。总之，这表明弱视抑制不能用正常的双眼视差掩蔽来解释，而更可能是输入的衰减。
