Macular degeneration is a disorder of the retina (the light sensitive membrane lining the inner surface of the back of the eye). The macula is the small central area of the retina used for central vision (for reading, watching TV, recognising faces, driving). Macular degeneration can result in diminished central vision.

Incidence/age

Macular degeneration is the leading cause of impaired vision in individuals over 50 years of age in Ireland. It occurs rarely in younger patients.

Causes

Macular degeneration is thought to occur as part of the body's natural ageing process.

Signs/symptoms

Patients with macular degeneration may experience blurring, dimming or distortion of the centre of the vision. Straight objects such as the edge of a door may appear bent. Difficulty in reading, carrying out close work or driving may be experienced.

Although the central vision is affected, in the vast majority of cases the peripheral (side) vision is spared. This allows, for example, a patient to see the outline of a head but have difficulty making out the facial features. There may be a loss of colour vision from the affected eye.

In many cases little or no change occurs over a number of years whereas in others there is a slow progressive loss of the central vision. Occasionally there is sudden loss of the central vision due to leakage from tiny blood vessels under the macula.

Complications of disorder

Approximately 10% of cases will develop a disciform macular degeneration. This is caused by sudden leakage from tiny blood vessels under the macula. With time the affected area will heal with a scar which has a more severe effect on a larger area of the central vision.
Tests

An Amsler grid test in which a patient looks at a dot in the centre of a grid drawn on a piece of paper is used to detect areas of distortion or loss of the central vision.

A colour vision test may be used to detect loss of colour vision.

A fluorescein (or indocyanine green) angiogram may be carried out if the presence of leaking blood vessels under the macula is suspected. The pupils are dilated with drops and an injection of dye is given into a blood vessel in the arm.

The dye will circulate throughout the body and as it passes through the eye photographs of the blood vessels at the back of the eye are taken. This will demonstrate abnormal or leaking blood vessels under the macula and will indicate whether laser treatment would be of benefit.

Treatment

Medical Treatment
Unfortunately there is no cure for macular degeneration. In some cases where there is a leaking blood vessel adjacent to the macula then laser treatment may be indicated to seal the blood vessel and slow the progression of the disease.

Although the disease cannot be cured usually the side or peripheral vision is not affected and most patients with macular degeneration can be helped to see better. Many are helped with reading with the help of optical aids.

These can include large print books, books on tape, computer readers, better lighting, and training in the use of peripheral vision. There are a large range of visual aids available and a careful assessment by an ophthalmologist or by an optician will be necessary to find the aid best suited to each individual.

In some patients the central vision may fall to a very low level and these patients benefit from being registered as a visually handicapped person. A visit at home will then be carried out by a vision impairment officer trained in visual handicap who will advise on ways of improving safety in the home, coping better with daily activities and explain the benefits that are available to the visually handicapped person.

Because of the large numbers of patients in the population affected by macular degeneration considerable research throughout the world has been carried out in an attempt to find alternative treatment and prevention options. Nutritional and dietary factors such as vitamin supplementation have not been shown at the present time to be of benefit to patients with macular degeneration. Alternative treatment options which are at present the subject of research evaluation but which are still in clinical trials include radiation therapy and photodynamic therapy.

Surgical Treatment

In a limited number of patients it is possible to carry out vitrectomy surgery within the eye to obtain access to the space between the retina and the back wall of the eye to remove the tiny blood vessels responsible for leakage leading to disciform macular degeneration. This surgical technique is being evaluated through clinical trials to establish what benefit is achieved following the operation and which patients would be appropriate for the operation.

A number of surgical techniques for the treatment of macular degeneration are being explored. These include retinal translocation (the rotation of the retina) to move the damaged macula away from the centre of the retina. These techniques are very experimental and, while research continues, have not yet been shown to be a proven benefit to patients with macular degeneration.

The use of a retinal prosthesis (microchip on the retina) has been explored for patients wth severe retinitis pitmentosa but is unlikely to be of benefit to patients with macular degeneration.
Outcome

Macular degeneration can vary in severity between individuals. The condition may be very mild in the early stages with a minimal effect on vision. In some cases only one eye is affected and one eye continues to see well for many years. Even when both eyes are involved macular degeneration usually affects only the central portion of the vision and the side or peripheral vision is retained. The remaining sight can be very useful and many people can continue with their favourite activities with the use of optical aids.

Patients with macular degeneration can use their eyes as much as they wish. It is not possible to wear the eyes out from over use.

In order to detect early loss of vision associated with macular degeneration patients are recommended to self test their eyes using the Amsler grid. This involves looking at a square grid made up of criss cross lines with a dot in the centre. The grid is held 12" from the face and reading spectacles are used if appropriate.

The lines of the grid should all be straight and continuous. If the lines are wavy, distorted or blurred or if there are missing or broken areas on the grid then the significance of this should be discussed with the optician or the ophthalmologist at an early stage. Early evaluation is important because laser treatment, if it is suitable, is only effective in the early stages of the condition.