How does the eye focus light?

The eye focuses light through the cornea and lens, which refract light to create a clear image on the retina.

The process of focusing light in the eye is a complex one, involving several different parts of the eye. The first step in this process occurs when light enters the eye through the cornea, the clear front surface of the eye. The cornea refracts, or bends, the light that enters the eye, beginning the process of focusing it.

After passing through the cornea, the light then travels through the pupil, the small black hole in the centre of the iris, the coloured part of the eye. The size of the pupil can change, controlled by the iris, to regulate the amount of light entering the eye. In bright light, the iris contracts to make the pupil smaller and reduce the amount of light entering the eye. In dim light, the iris relaxes to make the pupil larger and allow more light into the eye.

The light then reaches the lens, a clear structure located behind the iris and pupil. The lens further refracts the light, focusing it onto the retina, the light-sensitive layer at the back of the eye. The lens can change shape, becoming thinner or thicker, to adjust the eye's focus and allow us to see objects clearly at different distances. This process is known as accommodation.

The ciliary muscles, which are attached to the lens, control the shape of the lens. When these muscles contract, they cause the lens to become thicker, increasing its refractive power to focus on near objects. When the ciliary muscles relax, the lens becomes thinner, reducing its refractive power to focus on distant objects.

Finally, the light that has been focused by the cornea and lens forms an image on the retina. This image is then converted into electrical signals by the photoreceptor cells in the retina, which are sent to the brain via the optic nerve, allowing us to perceive the image.