Patient Information for Eye Diseases

To understand the different eye diseases, conditions, and treatments  it is helpful to understand the structure of an eye. This is a photograph of the inside of the eye, viewed from the side. As you will see, the eye works much like a camera with specialised structures that help focus light and others that make the picture.

Cornea

This is the clear surface of the eye through which light enters the eye. It is normally bathed by tears. Any abnormalities here, including astigmatism, can cause blurred vision.

Aqueous Humor

This is the liquid structure that is located between the cornea and the iris. It is formed by the ciliary body. The treatment of glaucoma, for example, involves managing how aqueous is produced by and drains from the eye.

Iris

This is the coloured part of the eye that forms the pupil. It is important in regulating the amount of light entering the eye. Disorders and diseases of the iris can include inflammation (uveitis) that needs to be treated urgently.

The Lens

This is the structure that focuses light onto the retina. If the lens is cloudy, the quality of the light entering the eye will be poor. This will cause blurred vision and difficulty managing in the dark. When the lens becomes cloudy, it is called a cataract.

Zonule Fibres

These are arranged like the spokes of a bicycle wheel and extend from the ciliary body to the edge of the lens. They suspend the lens in the centre of the pupil. The length of the fibres is modified by the eye to focus the lens at different distances. This ability reduces with time, making it harder to focus on near objects such as when reading. Multifocal lenses during cataract surgery are one option to address this.

Ciliary Body

This is a specialised ring of muscle that makes the aqueous humor and also helps to change the focusing power of the lens. This helps us remain focused on what we need to see at different distances such as when driving or reading.

The sclera and conjunctiva

This is the thick, protective ‘skin’ of the eye and is white in colour. Blood vessels are present on the surface. This is covered by a clear membrane called the conjunctiva. Red eyes can develop from a variety of inflammatory disorders including dry eyes, as a result of inflammation of the conjunctiva or layers of the sclera.

Vitreous Humor

This is a clear gel-like structure that is located between the lens and the retina. It is normally attached to the retina at certain points. With time, the gel-like structure becomes more liquid in nature and there may be more opaque fibres that float within the vitreous. These can interfere with the passage of light through the eye and give rise to the symptom of floaters. Depending on the cause of floaters, it may be possible to treat them with a painless and quick laser procedure called YAG vitreolysis.

Retina

This is a very important layer of nerves and fine blood vessels. It works in a similar manner to a film in a camera and it captures light and converts this into electrical impulses. These are then transmitted to the relevant parts of the brain through a series of nerves to make the picture that we all see. This structure can be damaged by eye diseases such as age-related macular degeneration, diabetic eye disease or vein occlusions. These need to be diagnosed quickly and urgent treatment given when necessary to prevent permanent sight loss.

The Fovea

This area measures about 0.3 mm in diameter and is located near the centre of the retina. It is this part of the retina that can determine the fine detail in what we see such as small letters or facial features. This is the vision we enjoy. The rest of the retina is more important in determining shapes and sees larger objects. Any abnormalities of the fovea can cause a dramatic reduction in vision and needs urgent assessment.

The Optic Nerve

This functions in a similar way to a cable, carrying electrical impulses made by the retina to the brain. Abnormalities of the optic nerve occur in diseases such as glaucoma and multiple sclerosis.

The Choroid

This is a rich network of blood vessels that lies immediately below the retina. It is important in nourishing a part of the retina. However abnormal blood vessels can develop in diseases such as age-related macular degeneration or in very short sighted (myopic) eyes requiring urgent treatment to prevent permanent sight loss.