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The plica semilunaris is a small fold of bulbar conjunctiva on the medial canthus of the eye.It functions during movement of the eye, to help maintain tear drainage via the lacrimal lake, and to permit greater rotation of the globe, for without the plica the conjunctiva would attach directly to the eyeball, restricting movement. [1]
The nictitating membrane of a masked lapwing as it closes over the left eye, originating from the medial canthus. The nictitating membrane (from Latin nictare, to blink) is a transparent or translucent third eyelid present in some animals that can be drawn across the eye from the medial canthus to protect and moisten it while maintaining vision.
Eyelid edema is a condition in which the eyelids are swollen and tissues contain excess fluid. It may affect eye function when it increases the intraocular pressure. Eyelid edema is caused by allergy, trichiasis or infections. [4] The main symptoms are swollen red eyelids, pain, and itching. Chronic eyelid edema can lead to blepharochalasis.
Humans have two eyes, situated on the left and the right of the face. 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
An epicanthic fold or epicanthus [6] is a skin fold of the upper eyelid that covers the inner corner (medial canthus) of the eye. [3] However, variation occurs in the nature of this feature and the possession of "partial epicanthic folds" or "slight epicanthic folds" is noted in the relevant literature.
All geckos except those in the subfamily Eublepharinae (eyelid geckos) possess brilles. Some groups of bony fish have a transparent eyelid known as the adipose eyelid. [3] Some reptiles, mammals and birds have a translucent third eyelid that moves horizontally across the eye called the nictitating membrane. [4]
Entoptic phenomena (from Ancient Greek ἐντός (entós) 'within' and ὀπτικός (optikós) 'visual') are visual effects whose source is within the human eye itself. (Occasionally, these are called entopic phenomena , which is probably a typographical mistake.)
The parietal eye (very small grey oval between the regular eyes) of a juvenile bullfrog (Lithobates catesbeianus) Adult green anole (Anolis carolinensis) clearly showing the parietal eye (small grey/clear oval) at the top of its head Parietal eye of the Merrem's Madagascar swift (Oplurus cyclurus) is surrounded by a black-and-white spot on the skin, giving it the "three-eyed" appearance