A new counterintuitive training for adult amblyopia

Abstract

Objectives: The aim of this study was to investigate whether short-term inverse occlusion, combined with moderate physical exercise, could promote the recovery of visual acuity and stereopsis in a group of adult anisometropic amblyopes.

Methods: Ten adult anisometropic patients underwent six brief (2 h) training sessions over a period of 4 weeks. Each training session consisted in the occlusion of the amblyopic eye combined with physical exercise (intermittent cycling on a stationary bike). Visual acuity (measured with ETDRS charts), stereoacuity (measured with the TNO test), and sensory eye dominance (measured with binocular rivalry) were tested before and after each training session, as well as in follow-up visits performed 1 month, 3 months, and 1 year after the end of the training.

Results: After six brief (2 h) training sessions, visual acuity improved in all 10 patients (0.15 ± 0.02 LogMar), and six of them also recovered stereopsis. The improvement was preserved for up to 1 year after training. A pilot experiment suggested that physical activity might play an important role for the recovery of visual acuity and stereopsis.

Conclusions: Our results suggest a noninvasive training strategy for adult human amblyopia based on an inverse-occlusion procedure combined with physical exercise.

Figure 1

Pilot experiment results. Five out of the 10 patients recruited for the study performed a pilot experiment. In three consecutive days, the non‐amblyopic eye was patched without the simultaneous physical exercise training. (A) LogMar visual acuity plotted as a function of time from the beginning of the pilot experiment (different symbols colors represent individual patient's performance). Only a small improvement in visual acuity was observed. (B) LogMar stereo‐threshold plotted as a function of time from the beginning of the pilot experiment (C) Comparison between the visual acuity improvement observed in the pilot experiment and after the first 3 days of training in the main experiment combining monocular occlusion and physical exercise (different symbols for single subjects, bars: average visual acuity). The visual acuity improvement is significantly larger (bootstrap sign test, ***P < 0.001) for the main experiment.

Figure 2

Training induces a recovery of visual acuity and stereo‐threshold. (A) LogMar visual acuity plotted as a function of time from the beginning of training. To achieve a robust quantification of visual acuity, each point represents the average of three different ETDRS charts. Different symbol colors represent the individual subjects’ performances after each training session. (B) Stereo‐thresholds plotted as a function of time from the beginning of training. Stereo‐thresholds were obtained using the TNO test. For subjects showing course stereopsis with the TNO test (S3, S8, S11), stereo‐thresholds were obtained using the LANG stereo‐test.

Figure 3

Visual acuity and stereo‐threshold in follow‐up measurements. Box plots showing visual acuity (A) and stereo‐thresholds (B) measured before and after 4 weeks of training and in follow‐up measurements obtained 1 months, 3 months, and 1 year after the end of training. Box plot explanation: upper horizontal line of box, 75th percentile; lower horizontal line of box, 25th percentile; whiskers, 10th and 90th percentile. Squares represent means.

Figure 4

Correlations between anisometropia, visual acuity improvement, and fixation quality. (A) Scatter plot of the LogMar visual acuity measured for each subject (different symbol colors) before training (x‐axis) and the difference between visual acuity measured after and before the 4‐week training (y‐axis). No correlation is observed between initial anisometropia and visual acuity. (B) Scatter plot reporting the percentage of fixations falling within a 2° radius from the fixation cross presented inside a microperimeter obtained before and after training. No consistent change in fixation quality is observed across subjects.

Figure 5

Sensory eye dominance changes after training. (A) Sensory eye dominance assessed before and after each 2 h training session (amblyopic eye occlusion + physical exercise), averaged for each subject across training sessions, different symbols colors for different subjects. (B) Proportion of mixed percepts measured before and after short‐term monocular deprivation combined with physical exercise, different symbols colors for different subjects (paired‐samples bootstrap sign test, ***P < 0.001, *P < 0.05). (C) Ocular dominance index measured at each training session before deprivation. The red line represents the linear fit of the data, the slope is significantly (F(1, 4) = 39.9, P = 0.004) higher than 0, indicating a positive trend. (D) Same as (C) but for the proportion of mixed percepts, the slope is significantly (F(1, 4) = 65.5, P = 0.0013) lower than 0, indicating a negative trend. Error bars represent 1 ± SEM.