ABSTRACT
Vision is perhaps the most remarkable of the senses. The human eye has been likened to a camera in many descriptions and indeed, superficially, this is true. Processing of images, their meaning and the context within which they appear is distributed throughout various parts of the brain and not presently fully understood. The visual cortex, however, is primarily responsible for perception of patterns and shapes encoded by the retina. The coloured portion of the eye, the iris, controls the amount of light entering the visual system by changing the size of the pupil, the dark centre, in a similar manner to a lens aperture. The eye may be considered as comprising three tunics, or layers, identified as the fibrous, vascular and nervous tunics. These approximately correspond to the outer, middle and inner layers of the wall of the eye. Beginning at the edge of the cornea, the conjunctiva is a membrane that covers the outer part of the sclera.
