The retina is the light-sensitive layer of tissue coating the inside of the eye. Light entering the eye is focused by the cornea and lens before hitting the photoreceptors in the retina. It then triggers a series of chemical reactions in the two types of photoreceptors, the rods (for low light and peripheral vision) and cones (for detail, central and colour vision), and a nerve impulse is sent through the nerve fibre layer of the retina, via the optic nerve, to the brain where the image is interpreted. The retina needs a good supply of oxygen which is brought in through retinal arteries and de-oxygenated blood is taken away by retinal veins. These create a network across the retina from the optic nerve to the periphery.
The optic nerve connects the eye to the brain. Information is carried via nerve impulses from the retina through the optic nerve to the visual cortex in the brain, where it is interpreted into images. The optic nerve is a direct extension of the brain and is visible at the optic disc, where it enters the eye and can be seen when looking inside the eye.
The Optic Disc
The optic disc (or optic nerve head) is the visible cross section of the optic nerve where it enters the eye. The outer rim of the optic disc contains the nerve fibres from the retina and the hollow ‘cup’ in the middle is the space through which blood vessels (arteries and veins) travel in and out of the eye supplying it with oxygen (arteries) and taking deoxygenated blood away (veins).
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