Macular degeneration

Macular degeneration

What is macular degeneration?

The macula is the point of the retina on which light rays are focused by the cornea and the lens of the eye. Like the film in a camera, the retina is responsible for transforming focused light into an image which the brain can process.

If the macula is damaged, the central part of the image is blocked out or blurred, while the image around the blurred area may be unaffected.

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Macular degeneration is a group of chronic diseases which cause breakdown of the macular tissues. It does not cause complete blindness, but can make reading or close work very difficult or impossible.

Although macular degeneration often occurs in older people, age alone is not the only reason for central visual loss. The most common form is called atrophic macular degeneration, and accounts for about 70% of cases. It is caused by thinning or breakdown of tissues in and beneath the macula.

fig1About 10% of cases are associated with membranes of new blood vessels forming under the retina. Normal blood vessels have strong walls and do not leak, but these vessels are brittle, and cause fluids to accumulate under the retina, impairing its function. Sometimes they rupture and bleed, leading to scar tissue which impairs the function of the macula severely. Other diseases, like hypertension, may worsen macular degeneration. One of the worst risk factors is cigarette smoking, with central visual loss and recurrence of blood vessel membranes six times as common as in non-smokers. Many other factors may contribute but are not yet proven, such as nutrition, exposure to bright light (especially blue and ultraviolet frequencies), and genetic factors. It is more common in some families and people of certain ethnic origin. Others seem to have some form of genetic protection, such as people from central and west African origin, in whom macular degeneration is very rare.

Other types of macular degeneration may be inherited, and often start in youth. Injury, infection or inflammatory conditions may also damage the delicate macula.

If only one eye is affected, the condition is hardly noticeable in the early stages. It may take some time before a patient notices visual disturbance.

Macular degeneration causes different symptoms. Sometimes only one eye is affected, and the fellow eye continues to see well for many years. If both eyes are affected, reading and close work becomes progressively more difficult. Since peripheral vision is usually unaffected, most people can take care of themselves quite well.

Other symptoms include reduced color vision, distortion of straight lines, and empty or dark areas in the centre of the visual field.

Diagnosis
Many patients are unaware of problems until vision becomes blurred. Your ophthalmologist can detect macular degeneration in the early stages, before vision is affected. Instruments allowing high magnification and illumination of the retina are used to see if any damage is present. Additional tests may be required to determine the nature and extent of the damage. The most important of these is retinal angiography. High resolution photographs of the retina, macula and their blood vessels are taken while specific dyes are injected into a vein on the hand or forearm. These dyes allow detailed study of the integrity of retinal tissues and blood vessels, and also assist in deciding whether treatment is possible or appropriate. Doing an OCT scan of the eye is an extremely helpful way to visualise the condition of the various layers inside the eye and specific the retina and macula.

Treatment and new developments
At this stage, atrophic macular degeneration is still largely untreatable. However, it is usually slowly progressive and allows many patients to learn how to use low vision devices, which assist in applying the remaining side vision more effectively. New directions in research which hold promise, are transplantation of stem cells. Macular translocation, a new surgical procedure, may also be of benefit.
Laser treatment is very useful in cases where abnormal blood vessel membranes are present under the retina. The laser is used to seal leaking membranes and destroy abnormal blood vessels. It is mainly intended to prevent further damage, rather than improve vision, and only certain patients can expect to have improved vision again. Injecting anti VEGF drugs into the eye is also effective in many cases to stop the formation of new harmful abnormal blood vessels.
Surgical excision of membranes under the retina is now performed routinely, with modest but very promising results.
Electrical stimulation of the eye with pulsed currents, as used in several pain control devices, is a new field of research which may benefit selected patients.
Photodynamic therapy (PDT) is still experimental and not yet commercially available, but offers hope of significant recovery in a previously untreatable group of patients. Basically, it consists of injecting an inactive substance into a vein on the hand or arm. This collects in the abnormal tissues of subretinal membranes, where it is activated with a low-energy, harmless infrared laser. Much less damage is caused than with conventional laser techniques when the fovea, or centre of the macula, is involved. However, further research is required and long term results are awaited.

The latest and most exciting development is a new surgical technique, called macular translocation. In this complex operation, the retina is deliberately detached from the inside of the eye. The macula is then repositioned over an area of healthier pigment tissues, allowing it to regain function. The eye itself is also then modified to align the new macular position to the visual axis, allowing normal straight – ahead vision. Remarkable results have been achieved with this technique.

The investigation and treatment of macular degeneration does not fall in the interest field of all ophthalmologists, due to the challenges involved and difficulty in treatment. Patients should select an ophthalmologist with a specific interest in this and other retinal conditions, who is experienced in the current techniques.

If you are over 50, or if you have a family history of retinal problems, you should have your eyes examined regularly for signs of problems like macular degeneration. Early detection and treatment, if required, may help to prevent severe visual loss.

 

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