The Status of Vernier Acuity Following Late Sight Onset.

We possess a remarkably acute ability to detect even small misalignments between extended line segments. This "vernier acuity" significantly exceeds our "resolution acuity"-the ability to resolve closely separated stimuli-and is generally considered a "hyperacuity," since the detectable misalignments are markedly finer than the diameter of single retinal cones. Vernier acuity has, thus, often been proposed to reflect spatial organization and multi-unit cortical processing, rendering it an important index of visual function. Notably, vernier acuity exhibits a characteristic developmental signature: it is inferior to resolution acuity early in life but eventually exceeds it by up to one order of magnitude. However, vernier acuity may be disproportionately sensitive to developmental disruptions. Here, we examined the resilience of acquiring this visual proficiency to early-onset, prolonged deprivation by longitudinally tracking vernier and resolution acuities in children with dense congenital cataracts who gained sight late in life as part of Project Prakash. Our data reveal marked longitudinal improvements in both acuity measures and also demonstrate that, like the normally-sighted, late-sighted individuals' vernier acuity exceeds their resolution acuity, thereby rendering it a hyperacuity. However, the extent of this hyperacuity is weaker than observed in normally-sighted controls, pointing to partial limitations in postsurgical skill acquisition. Despite these constraints, our findings point to the feasibility of forming some integrative circuits in the visual system even when inputs are severely compromised, and to the availability of some residual plasticity late in childhood, with implications for the rehabilitation prospects of children following treatment for congenital cataracts.