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The pupil of the human eye can range in size from 2 mm to over 8 mm to adapt to the environment. The human eye can detect a luminance from 10 −6 cd/m 2, or one millionth (0.000001) of a candela per square meter to 10 8 cd/m 2 or one hundred million (100,000,000) candelas per square meter.
The human eye is an organ which reacts to light for several purposes. As a conscious sense organ, the eye allows vision. Rod and cone cells in the retina allow conscious light perception and vision including color differentiation and the perception of depth. The human eye can distinguish about 10 million colors. [3]
Distribution of rods and cones along a line passing through the fovea and the blind spot of a human eye [11] While rods outnumber cones in most parts of the retina, the fovea , responsible for sharp central vision, consists almost entirely of cones.
Entoptic phenomena (from Ancient Greek ἐντός (entós) 'within' and ὀπτικός (optikós) 'visual'), occasionally and incorrectly referred to as entopic phenomena, are visual effects whose source is within the human eye itself.
The highest such number that the eye can resolve as stripes, or distinguish from a grey block, is then the measurement of visual acuity of the eye. For a human eye with excellent acuity, the maximum theoretical resolution is 50 CPD [43] (1.2 arcminute per line pair, or a 0.35 mm line pair, at 1 m).
[9] [10] He was the first person to explain that vision occurs when light bounces on an object and then is directed to one's eyes. [11] Leonardo da Vinci (1452–1519) is believed to be the first to recognize the special optical qualities of the eye. He wrote "The function of the human eye ... was described by a large number of authors in a ...
The human eye can function from very dark to very bright levels of light; its sensing capabilities reach across nine orders of magnitude. This means that the brightest and the darkest light signal that the eye can sense are a factor of roughly 1,000,000,000 apart. However, in any given moment of time, the eye can only sense a contrast ratio of ...
An important risk factor is increased intraocular pressure (pressure within the eye) either through increased production or decreased outflow of aqueous humour. [8] Increased resistance to outflow of aqueous humour may occur due to an abnormal trabecular meshwork or due to obliteration of the meshwork resulting from injury or disease of the iris.