Anatomy of the Eye

The eye is a fascinating and complicated organ that allows us to see the world around us. We are going to focus on each anatomical part that makes up the eye, following the path the light travels through it!

1 - Cornea

The front of the eye is protected by the cornea, a transparent covering of the pupil and iris. The cornea refracts the light entering the eye in order to focus on the object the person is looking at. The shape of the cornea can affect whether the person is long or short sighted, and if severely misshaped it can distort or blur vision at any distance, called astigmatism. Eye laser surgery can help to correct the shape of the cornea.

2 - Sclera

The white of the eyes, which are covered with a thin mucous membrane (conjunctivia), containing tiny blood vessels and underlining the undersurface of the eyelids. The sclera is a tough layer that covers and protects the whole eyeball. It is there to prevent injury and help the eyeball keep its shape. The sclera has muscles at different points that allow the eye to move around. These are the superior rectus, inferior rectus, lateral rectus, medial rectus, superior oblique, trochlea of superior oblique and inferior oblique muscles.

3 - Anterior chamber

The space between the cornea and the iris is known as the anterior chamber. It is filled with a watery fluid called the aqueous humour. The fluid is in constant supply and nourishes the inside of the eye. It before drains away through a narrow space at the outside of the iris where it is attached to the sclera. If the fluid does not drain away properly then pressure can build up and damage sight, causing glaucoma.

4 - Iris

This is the coloured part of the eye. Colours of eyes can include brown, blue, grey, green, black or hazel and this is affected by how much pigment or melanin is in the iris. The iris is designed to control the size of the pupil and therefore the amount of light that is allowed into the eye.

5 - Pupil

This is black opening into the eye. It sits in the centre of the iris and is black in appearance as the tissues inside the eye absorb the light as it enters, leaving no colour left behind in the pupil itself! The pupil dictates how much light can enter the eye. If there is not much light, then the pupil will dilate or grow bigger to let more in. If the light is too bright, the pupil can contract or grow smaller to limit how much light can enter the eye.

6 - Lens

The lens is transparent, which allows the light to pass through it and be focused on the retina. The lens is able to focus on objects whether they are near or far away with its ability to change shape, but around the age of 40 it starts to thicken which reduces this ability. Cataracts may also form which cause the lens to enlarge and become cloudy.

7 - Retina

The retina is at the back of the inner surface of the eye. It contains millions of photoreceptors, which are known as rods and cones, capturing light and turning them into electrical impulses. The rods work best in dim light, and offer night and peripheral vision. There are around 125 million rods in the retina. Cone cells are approximately six million in number and are found in the macular, an oval-shaped part towards the centre of the retina. They help sharpen vision, using bright light to see colour. Colours are less accurate when it is dark because cones need bright light to work properly. In the centre of the macular is the fovea. This area has most of the cone cells. It helps the eye to have sharp central vision.

8 - Optic Nerve

By the time the light reaches here, it’s not really light anymore, but actually electrical signals. The optic nerve connects the retina and the brain. Where the optic nerve leaves the eye, the retina stops, causing a ‘blind spot’.

Areas where the light does not touch, but are still very important!

The rest of the space in the eyeball that isn’t part of the viewing process is filled with a jelly-like substance called either the vitreous humour, vitreous body or just the vitreous. It helps the eye to maintain its spherical shape and helps to keep the pressure inside it constant. The gel also helps to keep the retina in place and provides nutrition.

In between the sclera and the retina is a layer of connective tissue and blood vessels called the choroid. The function of the choroid is to transport oxygen and nutrients to the retina. It also provides the blood supply to the macula and optic nerve.

Eye related AnatomyStuff resources: 
 
Anatomy of the Eye Chart / Poster - Laminated

Budget Giant Eye Model (6 times life size, 7 part)

Eye Model in Bony Orbit (5 times life size, 12 part)

Eye Model with Muscles and Nerves (6 times life size)


Pathological Eye Model
MICROanatomy Eye Model

Understanding Glaucoma Chart / Poster – Laminated

Further reading / sources

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