Sense organs

The structures of the eye include: cornea, iris, pupil, lens, retina, optic nerve, and blind spot. Each structure has a specific role in vision.

The cornea refracts (bends) light as it enters the eye, helping to focus the image onto the retina. The cornea is the first point of refraction in the eye.

The iris controls the amount of light entering the pupil by adjusting its size. In bright light, the iris constricts the pupil; in dim light, it dilates the pupil.

The lens focuses light onto the retina to create a clear image. It changes shape to allow focus on both near and distant objects, a process called accommodation.

The retina contains photoreceptor cells (rods and cones) that detect light and convert it into electrical signals. These signals are then sent to the brain via the optic nerve.

The optic nerve carries electrical impulses from the retina to the brain, where they are interpreted as images. It connects the eye to the visual cortex.

In bright light, circular muscles in the iris contract and radial muscles relax, causing the pupil to constrict. This reduces the amount of light entering the eye and protects the retina.

To focus on near objects, the ciliary muscles contract, reducing tension on the suspensory ligaments, making the lens thicker and more curved. This increases refraction of light.

To focus on distant objects, the ciliary muscles relax, increasing tension on the suspensory ligaments, making the lens thinner and less curved. This reduces the refraction of light.

Rod cells are highly sensitive to light and are responsible for night vision. They detect shades of gray and enable us to see in dim light conditions but do not detect colour.

Cone cells are responsible for colour vision and function best in bright light. There are three types of cones, each sensitive to different wavelengths of light (red, green, or blue).