The eye

The eye is a sense organ that contains receptors sensitive to light intensity and colour. Structures in the eye include:

• Retina: contains light-sensitive receptor cells: rods and cones that convert light into an electrical impulse. Cones allow you to see in colour when light intensity is high (daytime), while rods work in lower light intensities (night-time) but only enable black and white vision.
• Optic nerve: takes electrical impulses from eyes to the brain to generate an ‘image’.
• Sclera: outer layer that protects the eye (white in humans).
• Cornea: transparent layer that refracts light through the pupil.
• Iris: muscles surrounding the pupil that control the size of the pupil. Muscles contract and relax to control how much light enters the eye.
• Lens: changes shape to focus light on the retina.
• Ciliary muscles: contract/relax to change the shape of the lens.
• Suspensory ligaments: loosen and tighten to change lens shape.