Eyes and Vision

The eye is a complex organ composed of multiple specialized structures. The structures work together to capture light rays and transform them into nerve impulses that the central nervous system can analyze so that we can see.

Among the different types of electromagnetic radiation, only visible light can be perceived by the human eye.

The eye is made up of membranes, transparent structures, and multiple other structures. The eye is also protected by several accessory organs.

The eye is composed of three superimposed membranes, namely the sclera, the choroid, and the retina.

The eye is composed of four transparent structures: the cornea, the aqueous humour, the lens, and the vitreous humour (or vitreous body).

The eye includes many other structures such as the iris, the pupil, the optic nerve, and the lateral muscles.

The eye is a complex and fragile system. The accessory organs around the eye provide protection.

Objects must emit or reflect visible light to be seen by the human eye. Light rays travel in a straight line to reach our eye.

When light rays reach the eye, they first pass through the cornea which causes them to converge. The rays then pass through the aqueous humour and the pupil to reach the lens. The lens also converges light rays. They then pass through the vitreous humour to finally reach the retina.

The retina is the light path’s ending point. The cells of the retina actually transform the light rays into nerve impulses which are conveyed by the optic nerve to the central nervous system. The nervous system then analyzes the information received and interprets it in the form of images.

The retina includes multiple cells, called photoreceptors, that capture light and transform it into nerve impulses: the photoreceptors are called the cones and rods.

The cones are concentrated in an area called the yellow spot. They capture the colour of images. The rods make it possible to capture the contrast in the images, which is especially helpful in dim environments. They are mostly found around the edges of the yellow spot.

Where the retina attaches to the optic nerve, there are no photoreceptors, so no image is produced if the rays converge on this area. It is why the area is called the blind spot.

For the image perceived by the nervous system to be sharp, the light rays must reach a specific location on the retina. To do this, the lens changes in shape, changing the angle of refraction of the light rays. The lens is said to be accommodating.

So, when an observed object is moved away from the eye, the lens is at rest and has a flattened shape. When the object observed is close to the eye, the lens tends to bulge. Some vision disorders may result in the inability of the lens to sufficiently accommodate in order to create sharp images.