Contribution of Short-Time Occlusion of the Amblyopic Eye to a Passive Dichoptic Video Treatment for Amblyopia beyond the Critical Period

Abstract

Dichoptic movie viewing has been shown to significantly improve visual acuity in amblyopia in children. Moreover, short-term occlusion of the amblyopic eye can transiently increase its contribution to binocular fusion in adults. In this study, we first asked whether dichoptic movie viewing could improve the visual function of amblyopic subjects beyond the critical period. Secondly, we tested if this effect could be enhanced by short-term monocular occlusion of the amblyopic eye. 17 subjects presenting stable functional amblyopia participated in this study. 10 subjects followed 6 sessions of 1.5 hour of dichoptic movie viewing (nonpatched group), and 7 subjects, prior to each of these sessions, had to wear an occluding patch over the amblyopic eye for two hours (patched group). Best-corrected visual acuity, monocular contrast sensitivity, interocular balance, and stereoacuity were measured before and after the training. For the nonpatched group, mean amblyopic eye visual acuity significantly improved from 0.54 to 0.46 logMAR (p < 0.05). For the patched group, mean amblyopic eye visual acuity significantly improved from 0.62 to 0.43 logMAR (p < 0.05). Stereoacuity improved significantly when the data of both groups were combined. No significant improvement was observed for the other visual functions tested. Our training procedure combines modern video technologies and recent fundamental findings in human plasticity: (i) long-term plasticity induced by dichoptic movie viewing and (ii) short-term adaptation induced by temporary monocular occlusion. This passive dichoptic movie training approach is shown to significantly improve visual acuity of subjects beyond the critical period. The addition of a short-term monocular occlusion to the dichoptic training shows promising trends but was not significant for the sample size used here. The passive movie approach combined with interocular contrast balancing even over such a short period as 2 weeks has potential as a clinical therapy to treat amblyopia in older children and adults.

Figure 1

Illustration of the dichoptic movies. The two eyes' views are shown side by side. Complementary patterned image masks composed of irregularly shaped blobs were overlaid over the images seen by the two eyes. The shape and location of the blobs were varied dynamically every 10 seconds. (a) 100% contrast images were presented to the two eyes. (b) A 100% contrast image is presented to the left eye, and an image with a contrast reduced to 40% is presented to the right eye. Movie examples are available as supplementary material. Source video: Lauren Sauvan, wikimedia commons/CC-0.

Figure 2

Test stimuli illustrations. (a) qCSF stimulus illustration. In a single-interval identification task, the subject had to judge the orientation (horizontal or vertical) of a filtered noise pattern of varying spatial frequency and contrast. (b) Dichoptic letter chart illustration. Five letters of 2 c/d were presented at various contrasts to the left eye and 5 different letters with complementary contrasts to the right eye at the same spatial locations. So when viewed with both eyes, letters appeared overlapping on screen. Adapted from Kwon et al. [61]; Birch et al. [62].

Figure 3

Visual acuity improvement. (a) Visual acuity of the amblyopic eye (AE) of the participants reported at baseline, at the outcome of the training, and at the follow-up control one month later. (b) Visual acuity difference from the baseline of the amblyopic eye. (c) Visual acuity difference from baseline as a function of the initial acuity of the amblyopic eye. Participants from the patched group are indicated with filled grey symbols, and participants of the nonpatched group with open black symbols. Dashed lines represent linear regressions.

Figure 4

Contrast sensitivity improvement. (a) Contrast sensitivity of the amblyopic eye as a function of spatial frequency at baseline (solid line) and at the training outcome (dashed line) for the nonpatched group. Grey areas represent ±standard error. (b) Contrast sensitivity of the amblyopic eye as a function of spatial frequency at baseline and at the training outcome for the patched group. Same line style as (a). (c) Individual sensitivity gain of the participants at baseline, at the outcome of the training, and at the follow-up control one month later. Participants from the patched group are indicated with filled grey symbols, and participants of the nonpatched group with open black symbols.

Figure 5

Effect of training on binocular vision. (a) Interocular balance amblyopic/nonamblyopic eye expressed in dB at baseline, at the outcome, and at the follow-up of the training. (b) Disparity sensitivity threshold at baseline, at the outcome, and at the follow-up of the training. Participants from the patched group are indicated with filled grey symbols, and participants of the nonpatched group with open black symbols.