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NSR:National Skill Registry

CATAGORIES
Anatomy of Eye
The Cornea
The Iris & Pupil
Aqueous Humour
Vitreous Humour
The Lens
The Retina
The Optic Nerve
Cillary Muscle
Sclera
Choroid

Eye Anatomy – Aqueous Humour


Behind the cornea is the eye’s anterior chamber filled with fluid called aqueous humour (or just “aqueous”). This is how the cornea is nourished, since it lacks blood vessels. The aqueous bathes both the cornea and the lens, removing waste products as well as providing nourishment.

Three Main Corneal Layers

Epithelium – the top protective layer. It is five cells thick (50 microns). Epithelial cells are discarded and replaced continuously, which helps the eye to heal itself from any trauma or damage. The epithelium can regenerate itself entirely in about one week.
Tears keep the epithelium moist and wash out foreign bodies like dust or eyelashes. There are nerve endings in the epithelium, which is why it is painful when something scrapes or hits the eye.

Stroma – the layer that gives the cornea strength and keeps its curved shape. The stroma makes up about 90 percent of corneal thickness. It has several hundred sheets of collagen fibres, each just one to two microns thick. Because the fibres are equally spaced and regular, they maintain corneal transparency. They are embedded in a substance that holds water.
Stromal cells do not register pain. They also do not replace themselves, which is why laser vision correction is done on this layer – the changes will be permanent.

Endothelium – the layer that maintains equal water distribution in the cornea. If too much water builds up, the cornea starts to lose its transparency and impaired vision will result. The endothelium is just one cell thick and these cells pump out excess water. They are tightly packed and waterproof and form the cornea’s inner lining.
Endothelial cells cannot regenerate themselves. As we age, we slowly lose them at the rate of about ten percent each decade. Remaining cells enlarge to fill the gaps.



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