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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.
In addition, some uveal regions have special functions of great importance, including secretion of the aqueous humour by the ciliary processes, control of accommodation (focus) by the ciliary body, and optimisation of retinal illumination by the iris's control over the pupil. Many of these functions are under the control of the autonomic ...
Symptoms include eye pain, eye redness, floaters and blurred vision, and ophthalmic examination may show dilated ciliary blood vessels and the presence of cells in the anterior chamber. Uveitis may arise spontaneously, have a genetic component, or be associated with an autoimmune disease or infection .
The pupil function or aperture function describes how a light wave is affected upon transmission through an optical imaging system such as a camera, microscope, or the human eye. More specifically, it is a complex function of the position in the pupil [ 1 ] or aperture (often an iris ) that indicates the relative change in amplitude and phase ...
The pupil constricts when the iris sphincter muscle is stimulated and contracts In humans, it functions to constrict the pupil in bright light ( pupillary light reflex ) or during accommodation . [ citation needed ] In lower animals, the muscle cells themselves are photosensitive causing iris action without brain input.
With this simple geometrical similarity, based on the laws of optics, the eye functions as a transducer, as does a CCD camera. In the visual system, retinal , technically called retinene 1 or "retinaldehyde", is a light-sensitive molecule found in the rods and cones of the retina .
The extraneous pupil is c. 2.5mm away from the principal pupil. In cases of true polycoria there is an intact sphincter muscle, which contracts and dilates the pupils. [5] In an eye without polycoria, the sphincter muscle is a part of the iris that functions to constrict and dilate the pupil.
The pupil is the dark circular opening in the center of the iris and is where light enters the eye. By analogy with a camera, the pupil is equivalent to aperture, whereas the iris is equivalent to the diaphragm.