ABSTRACT
The eye consists of three layers enclosing its contents, the sclera, the choroid and the retina. The eye is divided into two by the lens. In front, the anterior and posterior chambers contain aqueous humor and behind the lens lies the vitreous humor. Aqueous humor is actively secreted by the epithelium of the ciliary body into the posterior chamber. The biconvex lens of the human eye has a diameter of 9 mm. It is encapsulated within an elastic connective tissue membrane which is attached to the suspensory ligament. The pupil light reflex controls the amount of light entering the eye by altering pupil size. This ranges between 1.5 and 8 mm in diameter, being maximal in complete darkness. For close objects, light rays are diverging as they enter the eye and so greater refraction is needed to bring them to focus at the fovea. This is achieved by the accommodation reflex.
