The Suppressive Basis of Ocular Dominance Changes Induced by Short-Term Monocular Deprivation in Normal and Amblyopic Adults

Abstract

Purpose: We aimed to study the effect of short-term monocular deprivation on the suppressive interocular interactions in normals and amblyopes by using a dichoptic masking paradigm.

Methods: Nine adults with anisometropic or mixed amblyopia and 10 control adults participated in our study. The contrast sensitivity in discriminating a target Gabor dichoptically masked was measured before and after 2 hours of monocular deprivation. The mask consisted of bandpass-filtered noise. Both the target and the mask were horizontally oriented at the spatial frequency of 1.31 cpd. Deprivation was achieved using an opaque patch on the amblyopic eye of amblyopes and the dominant eye of controls.

Results: Results were similar in both controls and amblyopes. After 2 hours of monocular deprivation, the previously patched eye showed a significant increase in contrast sensitivity under dichoptic masking, which also suggested reduced suppressive effect from the nonpatched eye. Meanwhile, the contrast sensitivity of the nonpatched eye remained almost unchanged under dichoptic masking.

Conclusions: We demonstrate that the ocular dominance changes induced by short-term monocular deprivation-namely, the strengthening of the deprived eye's contribution-are associated with the unilateral and asymmetric changes in suppressive interaction. The suppression from the nondeprived eye is reduced after short-term monocular deprivation. This provides a better understanding of how inverse patching (patching of the amblyopic eye) could, by reducing the suppressive drive from the normally sighted (nondeprived) eye, form the basis of a new treatment for the binocular deficit in amblyopia.

Figure 1.

(A) An illustration of the experimental procedure. The DE of normal controls or the AE of amblyopes was patched for 120 minutes. The contrast thresholds were measured before monocular deprivation (baseline) and 0 (T1), 5 (T2), 10 (T3), 15 (T4), and 30 (T5) minutes after monocular deprivation. (B) Dichoptic stimuli in a typical trial. The target and mask were dichotically presented to the tested eye and untested eye, respectively. Each trial began with an orange fixation point (200 ms), followed by a first interval stimulus (117 ms), an interstimulus interval with an orange fixation point (200 ms), then the second stimulus interval (117 ms), and a green fixation point until response. The target was presented in one of the two intervals, and the mask was presented in both intervals.

Figure 2.

Contrast sensitivity under dichoptic masking before monocular deprivation (baseline) in normal controls and amblyopes. On the x-axis is reported the contrast sensitivity of the eye subjected to interocular masking from the other eye. Error bars represent standard errors. Each dot/square represents one normal control/amblyope. The asterisk indicates a significant difference. **P < 0.01. ***P < 0.001.

Figure 3.

(A) Mean change in contrast sensitivity under dichoptic masking after monocular deprivation in normal controls. Results for the NPE (NDE) and the PE (DE) are shown in purple and green, respectively. (B) Change in contrast sensitivity under dichoptic masking after monocular deprivation for each normal adult (N1 to N10). Results for NPE (NDE) and PE (DE) are shown in purple and green, respectively. (C) Mean change in contrast sensitivity under dichoptic masking after monocular deprivation in amblyopes. Results for the NPE (FE) and the PE (AE) are shown in crimson and blue, respectively. (D) Change in contrast sensitivity under dichoptic masking after monocular deprivation for each amblyopic adult (A1 to A9). Results for NPE (FE) and PE (AE) are shown in crimson and blue, respectively. T1, T2, T3, T4, and T5 are the five time points (0, 5, 10, 15, and 30 minutes) at which we measured observers’ contrast thresholds after the removal of the patch. Error bars represent standard errors. Positive value represents improved sensitivity of the eye with target (reduced suppression from the eye with mask) after short-term monocular deprivation. Negative value represents reduced sensitivity of the eye with target (increased suppression from the eye with mask) after short-term monocular deprivation.

Figure 4.

The contrast sensitivity under dichoptic masking before and after 2 hours of monocular deprivation in normal adults (A) and adult amblyopes (B). The sensitivity of the two eyes at post-patching (y-axis) is plotted against the sensitivity at pre-patching (x-axis). In normal participants, results for the NPE (NDE) and the PE (DE) are represented by purple and green, respectively. In amblyopes, results for the NPE (FE) and the PE (AE) are represented by crimson and blue, respectively. The colored solid lines represent linear fits. T1, T2, T3, T4, and T5 represent the five time points (0, 5, 10, 15, and 30 minutes) after the removal of the patch. The data points in the shaded region represent the increased sensitivity of the tested eye to detect Gabor targets, which also represents the reduced suppression from the untested eye with mask after patching. The data points in the blank region represent the reduced sensitivity of the tested eye to detect Gabor targets, which also represents the increased suppression from the untested eye with mask after patching. The dashed unity line represents no change in sensitivity and suppression after patching. All P values were corrected by Bonferroni correction (P_c). Each dot/square represents one normal/amblyopic participant.

Figure 5.

The area under the changes in contrast sensitivity under dichoptic masking after the monocular deprivation versus time points curve (AUC) in normal controls and amblyopes. Error bars represent standard errors. Each dot/square represents one normal control/amblyope. The asterisk indicates a significant difference between the NPE and PE by paired t-test. *P < 0.05. ***P < 0.001. The sharp indicates a significant difference from 0 based on one-sample t-test. ^##P < 0.01. Positive value indicates increased sensitivity of the tested eyes to detect Gabor targets, as well as decreased masking effect from the untested eye after monocular deprivation. Negative value represents the opposite effect.