The third eyelid is a blinking membrane that exists in some animals.
It protects the eyes and moisturizes them without loss of visibility.
Sharks, birds and some reptiles have a full third eyelid.
In humans, the rudiment of a blinking membrane is called a lunate fold.
What is the third eyelid?
Semilunar fold (rudiment of the third century) isVertical fold of the mucosa (conjunctiva). It is located at the inner corner of the eyelids and is small in size. This fold is strongly developed in Negroes and Malayans and can contain cartilage, like the eyelids. It produces mucus, which collects foreign bodies (dust, dirt, causing damage to the cornea). Then they move into the tear duct and are removed from the eye. Near the semilunar fold is a teardrop. It has no specific functions. Pathologies in this area of the eye can cause disturbances in tearing.
Diseases of the semilunar fold and teardrop
Diseases of lacrimal flesh and semilunar foldsAre rare. They are manifested by developmental anomalies, dystrophic changes, inflammations, tumors. Anomalies in the development of the semilunar fold and teardrop are manifested by changes in their shape. In some cases, there is atrophy of the semilunar fold, it can cause lacrimation due to loss of contact of lacrimal points with the fluid.
Anatomically teardrop is an education,In its structure includes including sweat and sebaceous glands, fatty tissue, hair follicles. A person can develop purulent inflammation of a teardrop. The disease usually develops quickly and begins with sharp pains and redness in the inner corner of the eye, with a temperature increase, a malaise and a headache. The lachrymus sharply increases in size, with painful touching. Further in its tissues appear purulent plugs, which merge, forming an abscess. When the abscess breaks, the inflammation subsides, in the next four to five days recovery occurs.
With argyrosis (pigmentation) of the semilunar foldAppears dirty gray color, extending to the eyeball and conjunctiva of the eyelids. Pathology develops as a result of too long instillation of eye drops, which includes silver salts (collargol, silver nitrate, protargol). Argyrosis of a semilunar fold, teardrop does not affect the lacrimal function. Treatment for cosmetic purposes is ineffective, since this process is irreversible, silver particles can not be removed from the tissues.
In the lacrimal flesh can formBenign and malignant tumors. Most prevalent benign neoplasms (papillomas, adenomas, fibromas) there are polyps, cysts. Malignant tumors are predominantly melanoblastomas, sarcomas. On the semilunar fold, birthmarks are sometimes formed (nevi), which are developmental defects. In some cases, there is a tendency to their growth and malignant degeneration.