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The normal (monocular) human visual field extends to approximately 60 degrees nasally (toward the nose, or inward) from the vertical meridian in each eye, to 107 degrees temporally (away from the nose, or outwards) from the vertical meridian, and approximately 70 degrees above and 80 below the horizontal meridian. [7] [1] [8] [9]
A reference value above which visual acuity is considered normal is called 6/6 vision, the USC equivalent of which is 20/20 vision: At 6 metres or 20 feet, a human eye with that performance is able to separate contours that are approximately 1.75 mm apart. [9]
If the analogy of the eye's retina working as a sensor is drawn upon, the corresponding concept in human (and much of animal vision) is the visual field. [2] It is defined as "the number of degrees of visual angle during stable fixation of the eyes". [3] Note that eye movements are excluded in the visual field's definition.
Figure 1 - Humphrey field analyser. Humphrey field analyser (HFA) is a tool for measuring the human visual field that is commonly used by optometrists, orthoptists and ophthalmologists, particularly for detecting monocular visual field. [1] The results of the analyser identify the type of vision defect.
Visual acuity is the eyes ability to detect fine details and is the quantitative measure of the eye's ability to see an in-focus image at a certain distance. The standard definition of normal visual acuity (20/20 or 6/6 vision) is the ability to resolve a spatial pattern separated by a visual angle of one minute of arc.
At the low end of the range is the absolute threshold of vision for a steady light across a wide field of view, about 10 −6 cd/m 2 (0.000001 candela per square meter). [23] [24] The upper end of the range is given in terms of normal visual performance as 10 8 cd/m 2 (100,000,000 or one hundred million candelas per square meter). [25]
Snellen chart is used to estimate visual acuity (last three rows are 20/15, 20/13 and 20/10) A Snellen chart is an eye chart that can be used to measure visual acuity . Snellen charts are named after the Dutch ophthalmologist Herman Snellen who developed the chart in 1862 as a measurement tool for the acuity formula developed by his professor ...
In human vision, the useful field of view (or UFOV) is the visual area from which information can be extracted without eye or head movements. [1] UFOV size generally decreases with age, [ 2 ] most likely due to decreases in visual processing speed, reduced perception, and increased susceptibility to distraction.
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