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The cornea is the front-most part of the eye, and the corneal epithelium is a transparent, thin stratum that covers the exterior of the cornea. This stratum is usually made up of six or seven layers of cells, and is self-renewing, with cells being shed from the outermost layer and renewed from the deeper layers at a very fast rate. The corneal epithelium is the part of the eye that is most exposed to injuries, and damage to the epithelial tissue can lead to vision problems, pain, infection and other eye problems. Injuries and irritation can occur as a result of a variety of factors such as abrasions, vitamin A deficiency, eye disorders such as corneal ulcers and recurrent corneal erosion, and certain complications of laser eye surgery. Pain and discomfort in the eye can indicate damage to the corneal epithelium, and one should consult an eye care professional for diagnosis and treatment.
There are no blood vessels in the cornea to bring oxygen or required nutrients to the corneal cells or to the cells in the corneal epithelium. Instead, these cells receive their oxygen from the air and their nutrients from nerve fibers in the eye, tear fluid, and from the liquid substance located between the cornea and the lens. The corneal epithelium is constantly kept moist by tear fluid, and any problems related to tear production, such as dry eye syndrome or exposure to very dry air, can lead to discomfort.
Damage to the corneal epithelium can be the result of physical trauma, causing a corneal abrasion, or by inflammation or infection, causing corneal ulcers. These types of eye damage can lead to a painful eye disorder called recurrent corneal erosion. It occurs when the epithelial cells do not attach properly to the corneal tissue below the epithelium. Complications of LASIK surgery, a form of laser eye surgery, can also damage this part of the eye, causing a condition called epithelial ingrowth. This condition is rare, and only occurs when the procedure involves making a corneal flap to achieve vision correction.
Corneal epithelium cytology is the scientific study of the cells in this part of the eye. Some of this research has focused on the fast rate of cell self-renewal in the corneal epithelium, and specifically on the existence of corneal epithelial stem cells. Scientific studies show that transplanting such stem cells to patients suffering from vision loss due to various disorders and eye injuries, can improve vision and at least temporarily reverse blindness.