Retinitis pigmentosa

For those not familiar with the structure of the eye, think of it as similar to an old fashioned camera, which has a lens at the front, the purpose of which is to focus light onto a light sensitive film inside the camera towards the back. In a similar way, the eye is a sphere, with a lens at the front which focuses light onto a light sensitive tissue, which lines the inside of the back of the eye. This tissue is called the retina, a multi-layered delicate structure, which is the area affected by all types of RP. Over time the retina ceases to function and then dies away.

The lens at the front of the eye is normally completely transparent but can become opaque with increasing age or when there are diseases of the eye. An opaque lens is termed a cataract. A cataract can be treated by cataract surgery in which the opaque natural lens is removed and replaced by an artificial lens. Many elderly individuals develop cataract as a result of ageing changes in the lens. Patients with RP can develop cataracts at a younger age. The results of cataract surgery are usually excellent.

The onset of symptoms is variable but usually begins between the ages of 10 and 30, although some changes may become apparent in earlier childhood. In one type of early-onset RP, Leber congenital amaurosis, children are severely visually impaired at birth or in early infancy. By contrast, other types of RP may only show symptoms late in life.

In the more common types of RP, a person will first notice visual problems at dusk or in poor light, so-called night blindness, and also a gradual reduction in the peripheral field of vision, loss of the outer edges of vision (‘side vision’), resulting in a tendency to miss things or trip over things. At an early stage the central vision (‘straight-ahead and reading vision’) is unaffected. As the outer edges of the field of vision gradually disappear, the RP sufferer is left with the condition commonly referred to as “tunnel vision”.

Many people retain this central tunnel of useful vision until quite late in life, thereby being able to recognise faces and continue reading. The rate of loss of central vision is slower than that of peripheral visual field loss.

Retinitis pigmentosa can be classified according to its inheritance pattern. The different forms of RP result from the presence of one or two “faulty genes”. Genes are the instructions or recipes the body uses to build and repair itself. Genes determine many of your body characteristics including the colour of your hair and eyes. There are three possible inheritance patterns, Autosomal Dominant, Autosomal Recessive and X-Linked.