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The iris (pl.: irides or irises) is a thin, annular structure in the eye in most mammals and birds that is responsible for controlling the diameter and size of the pupil, and thus the amount of light reaching the retina. In optical terms, the pupil is the eye's aperture, while the iris is the diaphragm. Eye color is defined by the iris.
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. [ 18 ] [ 19 ] [ 20 ] (that is it has a range of 10 14 , or one hundred trillion 100,000,000,000,000, about 46.5 f-stops).
medium spring-open used to cut the external side of the cornea, fine sutures; iris, etc. •de' Wecker's iris scissors: small slender spring-open scissors for intraoccular maneuvers (iris and deeper and more delicate structures); has two wings to operate it and one sharp and one blunt blade. •Vannas' scissors
Muscles around the iris change the size of the pupil, regulating the amount of light that enters the eye [3] and reducing aberrations when there is enough light. [4] The eyes of most cephalopods , fish , amphibians and snakes have fixed lens shapes, and focusing is achieved by telescoping the lens in a similar manner to that of a camera .
"Orbit" can refer to the bony socket, [1] or it can also be used to imply the contents. [2] In the adult human, the volume of the orbit is about 28 millilitres (0.99 imp fl oz; 0.95 US fl oz), [3] of which the eye occupies 6.5 ml (0.23 imp fl oz; 0.22 US fl oz). [4]
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This process, which takes place during the first 5 years of life, gradually enlarges the eye socket. [3] [5] [13] Socket expansion through the use of implants of increasing size is another effective strategy. [3] [13] After socket expansion is complete, a painted prosthetic eye can be worn for cosmetic reasons. [13]
Polycoria is a pathological condition of the eye characterized by more than one pupillary opening in the iris. [1] It may be congenital or result from a disease affecting the iris. [ 1 ] It results in decreased function of the iris and pupil, affecting the physical eye and visualization.