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The pupil is the central opening of the iris on the inside of the eye, which normally appears black. The grey/blue or brown area surrounding the pupil is the iris. The white outer area of the eye is the sclera. The central outermost transparent colorless part of the eye (through which we can see the iris and pupil) is the cornea.
The iris consists of two layers: the front pigmented fibrovascular layer known as a stroma and, behind the stroma, pigmented epithelial cells.. The stroma is connected to a sphincter muscle (sphincter pupillae), which contracts the pupil in a circular motion, and a set of dilator muscles (dilator pupillae), which pull the iris radially to enlarge the pupil, pulling it in folds.
The eyes sit in bony cavities called the orbits, in the skull. There are six extraocular muscles that control eye movements. The front visible part of the eye is made up of the whitish sclera, a coloured iris, and the pupil. A thin layer called the conjunctiva sits on top of this. The front part is also called the anterior segment of the eye.
The sclera's blood vessels are mainly on the surface. Along with the vessels of the conjunctiva (which is a thin layer covering the sclera), those in the episclera render the inflamed eye bright red. [6] In many vertebrates, the sclera is reinforced with plates of cartilage or bone, together forming a circular structure called the sclerotic ring.
A limbal ring is a dark ring around the iris of the eye, where the sclera meets the cornea. [1] It is a dark-colored manifestation of the corneal limbus resulting from optical properties of the region. [2] The appearance and visibility of the limbal ring can be negatively affected by a variety of medical conditions concerning the peripheral ...
Eye color is an inherited trait determined by multiple genes. [14] [15] These genes are sought by studying small changes in the genes themselves and in neighboring genes, called single-nucleotide polymorphisms or SNPs. The total number of genes that contribute to eye color is unknown, but there are a few likely candidates.
The resulting eye is a mixture of a simple eye within a compound eye. Another version is a compound eye often referred to as "pseudofaceted", as seen in Scutigera . [ 28 ] This type of eye consists of a cluster of numerous ommatidia on each side of the head, organised in a way that resembles a true compound eye.
The uvea (/ ˈ j uː v i ə /; [1] derived from Latin: uva meaning "grape"), also called the uveal layer, uveal coat, uveal tract, vascular tunic or vascular layer, is the pigmented middle layer of the three concentric layers that make up an eye, precisely between the inner retina and the outer fibrous layer composed of the sclera and cornea.