Explanation

The choroid layer is thin over the posterior two third of the eyeball. But it becomes thick in the anterior part of form ciliary body. The ciliary body itself continues forward to form a pigmented and opaque structure called the iris which is the visible coloured portion of eye. The eyeball contains a transparent crystalline lens which is held in place by ligaments attached to ciliary body. In front of the lens, the aperture surrounded by the iris is called the pupil. This diameter of the pupil is regulated by muscle fibres of iris [image:21_image22.png]