Understanding the back of the eye
When you look at an object, light from the object passes through the cornea, then the lens, and then hits the retina at the back of the eye.
- The retina is basically made up of two layers. There is an inner layer of 'seeing cells' called rods and cones. These cells react to light and send electrical signals down tiny nerve fibres (which collect into the optic nerve) to the brain. The outer layer - the retinal pigment epithelium - is a layer of cells behind the rods and cones. These cells help to nourish and support the rods and cones. They pass nutrients from the blood vessels in the choroid to the rods and cones. They also take waste materials from the rods and cones to the blood vessels in the choroid.
*The rod cells ('rods') enable you to see shades of grey.
- The macula is a small but vital area of the retina at the back of your eye. It is about 5 mm in diameter. The very centre of the macula is called the fovea. The macula is the part of the retina that is the most densely packed with 'seeing cells' - especially cones.
- The choroids is a layer of tissue behind the retina which contains many tiny blood vessels. These help to take oxygen and nutrients to the retina.
- Bruch's membrane is a thin membrane which helps to form a barrier between the choroid and the delicate retina.
- The sclera is the outer thick white layer of the eye.
When you look at an object, the light from the object focuses on the macula. You need a healthy macula for detailed central vision such as when reading, writing, driving and recognising faces. The rest of the retina is used for peripheral vision - the 'side' vision which is not focussed. Therefore, without a macula you can still see enough to get about, be aware of objects and people, and be independent. However, the loss of central vision will severely affect normal sight.
What is age-related macular degeneration (ARMD)?
Age-related macular degeneration (ARMD) is a condition that occurs when cells in the macula degenerate. That is, they become damaged and die. Damage to the macula affects your central vision which is needed for reading, writing, driving, recognising people's faces and doing other fine tasks. There are two types - 'dry' and 'wet' ARMD - described below.
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