The eye can be compared to a camera. The pupil of the eye is like the aperture of a camera, regulating the amount of light entering the eye. Light is focussed by the cornea, the clear window into the eye, and the lens, which lies behind the pupil.
In the healthy eye, light passes through the lens and vitreous to reach the retina. The vitreous is a clear, jelly-like substance which occupies about two thirds of the volume of the eye. It is comprised of over 99% water, but also contains structural elements such as collagen fibres, proteins, and hyaluronan. The vitreous is normally attached to the retina in several areas, and so many disorders of the retina and vitreous are closely related.
The retina is the light-sensitive nerve tissue that lines the inner wall of the eye, like the film in a camera. Rays of light enter the eye, passing through the cornea, pupil and lens before focusing on to the retina. The retina contains photoreceptors which convert light into electrical impulses. In the healthy eye these impulses are sent via the optic nerve to the brain, where sight is interpreted as clear, bright, colourful images.
The retina lies on a layer of supporting tissue known as the retinal pigment epithelium or RPE. The RPE is important as it nourishes the photoreceptors and removes their waste products.
The macula is a small area at the centre of the retina. It is very important as it is responsible for our central vision. It allows us to see fine detail for activities such as reading, recognising faces, watching television and driving. It also enables us to see colour.
The choroid is the underlying vascular (blood vessel) layer of the eye from which the retina receives oxygen and nutrients.