Neuroplasticity and perceptual learning in adult amblyopia: rehabilitation perspectives from a systematic review and a pilot study

Introduction and objectives: amblyopia has traditionally been considered treatable only during childhood, within the critical period of visual development, which is generally assumed to extend up to approximately 8-10 years of age. However, evidence of adult neuroplasticity suggests that functional recovery may still be achievable beyond early developmental stages, and new techniques such as perceptual learning have emerged as promising approaches to induce adaptive changes in the visual system. This thesis aimed to evaluate the effectiveness of perceptual learning in adult amblyopia through a pilot study conducted at the NeuroVisUS laboratory, and to contextualize the results within the existing literature. Materials and Methods: a literature review was conducted, including 15 studies investigating perceptual learning using Gabor stimuli. At the same time, a single-case pilot study involved a 53-year-old woman with unilateral amblyopia undergoing a 24-day perceptual learning protocol with alternating occlusion. Outcome measures included visual acuity, visual acuity under crowding conditions, Vernier visual acuity, contrast sensitivity, and stereopsis. Results: the review demonstrated consistent improvements in visual acuity (pooled SMD = 3.44; 95% CI: 1.63–5.24), although with high heterogeneity (I² ≈ 99.2%). The pilot study data were analyzed on a weekly basis using linear regression to evaluate temporal trends over the intervention period. The results showed progressive improvements in visual acuity and Vernier visual acuity, following a non-linear trajectory. No changes were observed in stereopsis, and no effects of inverse occlusion were detected. Discussion: both the literature and the pilot study support the effectiveness of perceptual learning in adult amblyopia, suggesting the persistence of residual neuroplasticity in the adult visual system. However, the high variability observed across studies highlights the individual nature of outcomes. Improvements appear to primarily involve early visual processing functions, while binocular functions remain less responsive. In addition, no subjective improvements were reported. Conclusion: perceptual learning represents a promising yet highly variable approach for the treatment of adult amblyopia. Further large-scale studies and personalized interventions protocols are needed to optimize and better characterize treatment outcomes.