The human eye is approximately spherical and located in the orbit. The average diameter of normal adults is 24mm, the average vertical diameter is 23 mm, and the front end protrudes from the orbit 12 ~ 14 mm, which is protected by eyelids. The eyeball includes the wall of the eyeball, the inner cavity of the eye, contents, nerves, blood vessels and other tissues.
If the eyes are compared to a camera, the cornea is the lens of the camera, and eyelids and tears are the devices to protect the "lens". When we are unconscious, our eyelids blink. Every time we blink, tears will cover the corneal surface with a thin tear film to protect the "lens".
Because the cornea is transparent, there are no blood vessels on it. Therefore, the cornea mainly gets nutrition from tears. If the nutrients contained in tears are insufficient, the cornea will become dry and the transparency will decrease. Cornea also gets oxygen from the air, so many people will feel a little dry after waking up.
Extended data:
There is a lubricating film of tears on the surface of the eyeball, which is constantly refreshed with the blink of an eye to keep the eyes moist. If the air is always dry or absorbed, after about 10 seconds, dry spots will appear on the tear film and the surface of the eyeball will become drier and drier.
So in general, blink 10-20 times per minute. When you concentrate on reading or operating the computer, the blink frequency will be significantly reduced to about 5 times per minute.
Because the eyeball is dry, the eye between cornea and eyelid is easy to bruise when it is closed, which leads to dryness, fatigue, discomfort, inflammation and pain, and forms dry eye syndrome. If you don't pay attention to it, corneal ulcers and scars may appear, which will eventually lead to decreased vision.