Vernier acuity cards: examination of development and screening validity

Leveraging neural plasticity for the treatment of amblyopia

Amblyopia is a form of visual cortical impairment that arises from abnormal visual experience early in life. Most often, amblyopia is a unilateral visual impairment that can develop as a result of strabismus, anisometropia, or a combination of these conditions that result in discordant binocular experience. Characterized by reduced visual acuity and impaired binocular function, amblyopia places a substantial burden on the developing child. Although frontline treatment with glasses and patching can improve visual acuity, residual amblyopia remains for most children. Newer binocular-based therapies can elicit rapid recovery of visual acuity and may also improve stereoacuity in some children. Nevertheless, for both treatment modalities full recovery is elusive, recurrence of amblyopia is common, and improvements are negligible when treatment is administered at older ages. Insights derived from animal models about the factors that govern neural plasticity have been leveraged to develop innovative treatments for amblyopia. These novel therapies exhibit efficacy to promote recovery, and some are effective even at ages when conventional treatments fail to yield benefit. Approaches for enhancing visual system plasticity and promoting recovery from amblyopia include altering the balance between excitatory and inhibitory mechanisms, reversing the accumulation of proteins that inhibit plasticity, and harnessing the principles of metaplasticity. Although these therapies have exhibited promising results in animal models, their safety and ability to remediate amblyopia need to be evaluated in humans.

Amblyopia and the whole child

Amblyopia is a disorder of neurodevelopment that occurs when there is discordant binocular visual experience during the first years of life. While treatments are effective in improving visual acuity, there are significant individual differences in response to treatment that cannot be attributed solely to difference in adherence. In this considerable variability in response to treatment, we argue that treatment outcomes might be optimized by utilizing deep phenotyping of amblyopic deficits to guide alternative treatment choices. In addition, an understanding of the broader knock-on effects of amblyopia on developing visually-guided skills, self-perception, and quality of life will facilitate a whole person healthcare approach to amblyopia.

Development differentially sculpts receptive fields across early and high-level human visual cortex

Receptive fields (RFs) processing information in restricted parts of the visual field are a key property of visual system neurons. However, how RFs develop in humans is unknown. Using fMRI and population receptive field (pRF) modeling in children and adults, we determine where and how pRFs develop across the ventral visual stream. Here we report that pRF properties in visual field maps, from the first visual area, V1, through the first ventro-occipital area, VO1, are adult-like by age 5. However, pRF properties in face-selective and character-selective regions develop into adulthood, increasing the foveal coverage bias for faces in the right hemisphere and words in the left hemisphere. Eye-tracking indicates that pRF changes are related to changing fixation patterns on words and faces across development. These findings suggest a link between face and word viewing behavior and the differential development of pRFs across visual cortex, potentially due to competition on foveal coverage.

Population receptive fields (pRFs) in the visual system are key information-processors, but how they develop is unknown. Here, authors use fMRI and pRF modeling in children and adults to show that in the ventral stream only pRFs in face- and word-selective regions continue to develop, mirroring changes in viewing behavior.

Abnormal radial deformation hyperacuity in children with strabismic amblyopia

PURPOSE

In infants and toddlers, letter acuity is not a useful option, and grating acuity may underestimate the depth of strabismic amblyopia. Here, as a first step to establish the effectiveness of the paradigm as a clinical test, we assessed if radial deformation hyperacuity, known to be severely disrupted in adults with strabismic amblyopia, could be a potential test to detect and monitor strabismic amblyopia in young children.

METHODS

Fifty-one strabismic children and 130 normal controls ages 3 to 17 years participated. Radial deformation hyperacuity with three different radial frequency (RF) patterns (1° radius 8 RF, 0.5° radius 8 RF, and 1° radius 16 RF), optotype acuity, and grating acuity were measured. For strabismic children, hyperacuity and grating acuity were identified as normal/amblyopic based on age-matched norms. The normal/abnormal classification was compared with amblyopia diagnosis by gold standard early treatment diabetic retinopathy study (ETDRS) optotype visual acuity.

RESULTS

The 0.5° radius 8 RF pattern had 83% sensitivity and 71% positive predictive value (PPV) for strabismic amblyopia. In comparison, the 1° radius 8 RF and 1° radius 16 RF patterns had poorer sensitivity (27%-12%) and PPV (57%-50%) for amblyopia, similar to grating acuity (sensitivity = 38%, PPV = 31%). Amblyopic deficits using the 0.5° radius 8 RF pattern were directly proportional to optotype visual acuity deficits.

CONCLUSIONS

The demonstrated feasibility of radial deformation stimuli for forced-choice preferential looking testing and the sensitivity and specificity of the small radius radial deformation hyperacuity stimulus for amblyopia support the potential to utilize this test to detect and monitor amblyopia in infants and preschool children.