Cambridge O Level Biology · Syllabus 5090 · Coordination and Control
Lens
What is Lens?
A transparent, flexible, biconvex structure behind the pupil that refracts light and focuses it onto the retina. Its shape is changed by the ciliary muscles acting through the suspensory ligaments, which is how the eye focuses on near and distant objects.
This definition is part of the Coordination and Control chapter in Cambridge O Level Biology.
Questions students ask about Lens
What are the parts of the eye and what do they do?
The cornea refracts light entering the eye. The iris contains muscles that control the size of the pupil, which is the opening light passes through. The lens refracts light and focuses it on the retina, changing shape to do so. The ciliary muscles alter the tension in the suspensory ligaments, which are attached to the lens. The retina contains the light receptor cells, and the fovea is the region of the retina with the greatest density of them. The optic nerve carries impulses to the brain, and the blind spot is the point where it leaves, containing no light receptors.
What is accommodation?
Accommodation is the change in shape of the lens that focuses a sharp image of a near or distant object on the retina. For a near object the ciliary muscles contract, the suspensory ligaments slacken, and the lens becomes thicker and more convex, refracting light more. For a distant object the ciliary muscles relax, the suspensory ligaments tighten, and the lens becomes thinner and less convex, refracting light less. Accommodation does not change the size of the pupil.