The Clinical Use of Vernier Acuity: Resolution of the Visual Cortex Is More Than Meets the Eye

Abstract

Vernier acuity measures the ability to detect a misalignment or positional offset between visual stimuli, for example between two vertical lines when reading a vernier scale. It is considered a form of visual hyperacuity due to its detectable thresholds being considerably smaller than the diameter of a foveal cone receptor, which limits the spatial resolution of classical visual acuity. Vernier acuity relies heavily on cortical processing and is minimally affected by optical media factors, making it a useful indicator of cortical visual function. Vernier acuity can be measured, usually in seconds of arc, by freely available automated online tools as well as via analysis of steady state visual-evoked potentials, which allows measurement in non- or pre-verbal subjects such as infants. Although not routinely measured in clinical practice, vernier acuity is known to be reduced in amblyopia, glaucoma and retinitis pigmentosa, and has been explored as a measure of retinal or neural visual function in the presence of optical media opacities. Current clinical utility includes a home-based vernier acuity tool, preferential hyperacuity perimetry, which is used for screening for choroidal neovascularisation in age-related macular degeneration. This review will discuss the measurement of vernier acuity, provide a current understanding of its neuro-ophthalmic mechanisms, and finally explore its utility through a clinical lens, along with our recommendations for best practice.

A history of visual acuity testing and optotypes

“…The most important improvements of these optotypes are discussed next, ignoring numerous later modifications of the first examples, ending with some recommendations and conclusions. It will disregard stereoscopic acuity, Vernier hyperacuity [ 7 ], low-contrast optotypes, spatial frequencies or integrations, cortical visual functions [ 8 ] and ultra-low vision [ 9 ].…”

Scotopic Contour Deformation Detection Reveals Early Rod Dysfunction in Age-Related Macular Degeneration With and Without Reticular Pseudodrusen

“… 23 – 26 Photoreceptors form the front end of the neural visual system, and the visual process begins by sampling of the retinal image by the photoreceptor mosaic. 27 Therefore, cortically mediated vision tasks, such as hyperacuity, 28 , 29 would be predicted to be sensitive to disruption of the cone mosaic. Hyperacuity forms the basis of several tests that use shape discrimination or Vernier alignment to assess AMD severity 27 , 30 – 33 and monitor progression of wet AMD.…”