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How Your Eyes Work
The eye is a very complex organ with many different components that work together and allow us create images of our surrounding environment. Light rays first enter through the cornea, a transparent layer at the front of the eye and into the pupil, the dark circle positioned at the centre of the eye.
Depending on whether the incoming light is bright or dim, the pupil narrows or widens respectively, all of which is controlled by the iris. The lens is behind the iris and changes its shape, to focus incoming light on the retina. The retina is the tissue layer which lines the back of the eye and converts light it receives into neural signals which travel along the optic nerve and into the brain. The brain finally processes these signals which it receives from each eye to create images.
Watch this brief audio-visual by the National Eye Institute about the visual system and how it works.
Parts of Our Eyes
The cornea is the transparent outer layer of the eye that refracts, or redirects light and focuses it as it enters the eye.
The pupil is the dark hole in the centre of the eye that lets light in and depending on whether this is bright or dim light, the pupil widen or narrow respectively.
The iris is the coloured part of our eye and is responsible for adjusting the size of the pupil and controlling how much light reaches the retina.
The lens is a transparent structure inside the eye that works with the cornea to focus light on the retina. The lens can change shape, flattening to focus on objects far away and bending to focus on objects that are close.
The retina is a light-sensitive tissue that lines the back of the eye. It consists of rod and cone cells (photoreceptor cells). These cells collect the light signals directed onto them and send them as electrical signals to the optic nerve at the back of our eye.
The macula is the central part of the retina that allows us to achieve high-quality and central vision, helping us to read, drive safely and to see the world in detail and colour. The macula is yellow due to the collection of pigment from coloured fruit and vegetables we eat as part of our daily diet.
The fovea is the centre of the macula which provides the sharp vision.
Rod cells are concentrated around the edge of the retina. They help us to see things that are outside our central line of vision (peripheral vision) and recognise obstacles around us. Rod cells also enable us to see things in dim light.
Cone cells are concentrated in the centre of our retina where the light is focused by the cornea and lens. This area is called the macula. Cone cells give us our detailed vision which we use when reading and looking at people’s faces. They are also responsible for most of our colour vision.
The retinal pigment epithelium is a layer of cells located just outside the retina and is attached to the choroid. RPE cells form the blood-retina barrier and have a primary role in nourishing and maintaining the rod and cone photoreceptor cells.
The choroid is a layer containing blood vessels that lines the back of the eye; it is located between the retina and the sclera.
The sclera is the white outer coat of the eye, surrounding the iris.
The optic nerve carries information as electrical impulses from the retina to the brain where the visual images are formed.
This is the clear, jelly-like substance found in the middle of the eye that helps to regulate eye pressure and shape.