Editing Visual acuity (section)

== Other measures ==
Normally, visual acuity refers to the ability to resolve two separated points or lines, but there are other measures of the ability of the visual system to discern spatial differences.

[[Vernier acuity]] measures the ability to align two line segments. Humans can do this with remarkable accuracy. This success is regarded as'' [[hyperacuity]]''. Under optimal conditions of good illumination, high contrast, and long line segments, the limit to [[Vernier scale|vernier]] acuity is about 8 arc seconds or 0.13 arc minutes, compared to about 0.6 arc minutes (6/4) for normal visual acuity or the 0.4 arc minute diameter of a [[Fovea centralis|foveal cone]]. Because the limit of vernier acuity is well below that imposed on regular visual acuity by the "retinal grain" or size of the foveal cones, it is thought to be a process of the [[visual cortex]] rather than the retina. Supporting this idea, vernier acuity seems to correspond very closely (and may have the same underlying mechanism) enabling one to discern very slight differences in the orientations of two lines, where orientation is known to be processed in the visual cortex.

The smallest detectable visual angle produced by a single fine dark line against a uniformly illuminated background is also much less than foveal cone size or regular visual acuity. In this case, under optimal conditions, the limit is about 0.5 arc seconds or only about 2% of the diameter of a foveal cone. This produces a contrast of about 1% with the [[lighting|illumination]] of surrounding cones. The mechanism of detection is the ability to detect such small differences in contrast or illumination, and does not depend on the angular width of the bar, which cannot be discerned. Thus as the line gets finer, it appears to get fainter but not thinner.

[[Stereoscopic acuity]] is the ability to detect differences in [[depth perception|depth]] with the two eyes. For more complex targets, stereoacuity is similar to normal monocular visual acuity, or around 0.6–1.0 arc minutes, but for much simpler targets, such as vertical rods, may be as low as only 2 arc seconds. Although stereoacuity normally corresponds very well with monocular acuity, it may be very poor, or absent, even in subjects with normal monocular acuities. Such individuals typically have abnormal visual development when they are very young, such as an alternating [[strabismus]], or eye turn, where both eyes rarely, or never, point in the same direction and therefore do not function together.

Another test, including Visual acuity (EVTS/OptimEyes), uses targets which change in size, contrast, and viewing time. This test was developed by Daniel M. Laby with colleagues and uses [[item response theory]] to calculate a vision performance score (core score). This specific test of visual function has been shown to correlate to professional sports performance.<ref>{{Cite journal |last1=Laby |first1=Daniel M. |last2=Kirschen |first2=David G. |last3=Govindarajulu |first3=Usha |last4=DeLand |first4=Paul |date=2019-11-14 |title=The Effect of Visual Function on the Batting Performance of Professional Baseball Players |journal=Scientific Reports |language=en |volume=9 |issue=1 |page=16847 |bibcode=2019NatSR...916847L |doi=10.1038/s41598-019-52546-2 |issn=2045-2322 |pmc=6856529 |pmid=31728011}}</ref>