Visual acuity is defined as the size of the smallest letter that we can distinguish. Visual hyperacuity allows us to differentiate two straight lines with precision ten times more than visual acuity. The limits of this are in the mosaic of the sensory elements of the retina, whereas that depends on the processing that the brain does.
At present, it is not known very much which are the neurological mechanisms in the brain.
Estereopia tests, which study the limit of the three dimensions, are based on this capacity. Currently, the periphery of a preferred hyperacuity is being investigated, which is used to detect before changes, for example, in age macular degeneration.