Anatomy of Eye    

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The eye can be broken down into 6 main parts.

1. Cornea

The cornea is found at the front of the eye.  It is clear and shaped like a dome.  It is often compared with the lens of a camera, as it refracts or bends light that enters the eye so that it can be focused at the back of the eye, on the retina.  It is the most sensitive part of the human body because it has the most nerve endings.  It is about 1/2 millimetre thick in adults and is comprised of 3 layers; the Epithelium, the Stroma and the Endothelium.

The Epithelium is the layer of cells that cover the surface of the cornea.  It is about 5-6 cell layers thick and can regenerate itself if it is injured.  The Bowman’s Membrane lies beneath the epithelium and protects the cornea from injury, as it is very tough.  The stroma is the thickest layer of the cornea and is made up of collagen fibrils, which give the cornea its clarity.  The Descemet's Membrane lies between the stroma and the endothelium.  The main function of the epithelium is to stop foreign bodies from entering the eye, including dust and fluids.  It also absorbs oxygen and nutrients from tears. 

The Stroma, is made up of mainly water and also layered protein fibres which make it strong and elastic and helps to keep the eye well nourished.  It has a very unique makeup of protein fibres, which are essential in producing the cornea's light-conducting transparency. 

The Endothelium removes fluid from the corneal stroma, enabling the cornea to remain optically clear. 

2. Aqueous Humour

This is a clear, watery fluid, which fills the front of the eyeball.  It lies between the cornea and the lens.  The aqueous fluid circulates in the anterior chamber and small amounts continuously flow over the cornea keeping the corneal cells refreshed and removing old cells. The pressure in the aqueous helps to maintain the globe like shape.

3. Iris

This is the coloured part of the eye, which surrounds the pupil and allows light into the back of the eye. The iris widens and shrinks depending on the brightness of the object and this controls the amount of light entering the eye.

4. Crystalline Lens

This sits behind the iris and is akin to the focussing mechanism on a camera.  Ciliary muscles, attach the lens to the outer edges of the cornea.  The shape of the lens is changed by muscles, which expand, and contract to ‘accommodate’ for objects at different distances. This helps images to focus on the retina. 

5. Vitreous Humour

This is the clear gelatinous substance that fills the eyeball between the retina and the crystalline lens.

6. Retina

This is the light sensitive part of the eye, and is located at the back of the eye.  It contains photosensitive cells called rods and cones, which send messages to the brain.  Rods adapt to the dark and cones focus on colour work.  The rods are highly sensitive to light and dark changes, as well as shape and movement and many are located in the periphery of the retina.  Cones on the other hand, are not as sensitive to light as the rods but respond to green, red and blue colours.  Signals from the cones are sent to the brain, which then converts the messages into the perception of colour.  Cones work in bright light and rods work in dim light.  At the centre of the retina, lies the fovea, which is the centre of the eye's sharpest vision and the location of most colour perception.

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