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The Eye and Eye Conditions

Summary: Find out more about how the eye works and common eye conditions in Ireland.

The eye is made up of three parts.

  • The cornea and lens focuses light on the front of the eye.
  • The retina is a light-focusing film at the back of the eye.
  • The optic nerve connects each eye to the brain.

Your eye

An illustration of the eye, showing the iris, lens, macula and other areas.

How your eye works

The front skin on your eye is called the cornea. Its job is to focus light onto the front of the eye. The light passes through your pupil. The iris, the coloured part of your eye, is a round muscle that surrounds the pupil. The lens focuses the light to the back of your eye, called the retina. Tiny light-sensitive photoreceptors at the back of the eye send signals down fine wires to the brain. The wires joining each eye to the brain are known as the optic nerves.

Eye conditions

In Ireland, only a small number of babies are born with sight problems. Some people develop an eye condition as a result of an illness or accident but most people with sight loss are those whose eyesight has reduced as they get older. The most common eye conditions are macular degeneration, glaucoma, retinitis pigmentosa, cataracts and diabetic retinopathy.

Compare this image of what someone with 20/20 vision might see to the others below, which represent some eye conditions.

An image of two small children playing as a person with 20 / 20 vision might see

Macular degeneration

Macular degeneration is one of the leading causes of sight loss in Ireland, and usually occurs among people aged over 65 years. This condition causes a reduction in vision in the centre of the eye. The person’s side vision usually remains but they may have difficulty with seeing enough to see their watch, read and write, distinguish colours, or recognise people’s faces. People with macular degeneration almost never lose all of their sight.

Glaucoma and retinitis pigmentosa (RP)

Glaucoma and RP can cause tunnel vision. The person’s side vision is reduced but they may retain a small central area where they can still see enough to read and do fine work. Moving around can be very difficult, especially at night when vision is even more reduced.

Glaucoma and retinitis pigmentosa: An image of two small children play as a person with glaucoma or retinitis pigmentosa might see. There is no side vision but central vision only.


Most people with cataracts will regain most or all of their vision. A cataract is a clouding of the lens in the eye. For a person with cataracts, everything looks blurred and misty.

Cataract: An image of two small children playing as a person with cataract might see. The image is blurred.

Diabetic retinopathy

A person with diabetes has a higher chance of having diabetic retinopathy. People with diabetes need to have their eyes checked regularly. Damage to the back of the eye can often be repaired if detected at an early stage. Diabetic retinopathy causes blurring or patchy loss of vision.

Diabetic retinopathy: An image of two small children playing as a person with diabetic retinopathy might see. The image has patches missing.

All images courtesy of the National Eye Institute.