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Pathophysiology

Dry AMD

Dry AMD causes a gradual deterioration of the macula, usually over many years, as the retinal cells die off and are not regenerated. There is no current treatment for dry AMD. Around 10% to 15% of people with dry AMD go on to develop wet AMD. In wet AMD, abnormal blood vessels grow into the macula and leak blood or fluid which leads to scarring of the macula and rapid loss of central vision.

In the early stages of the disease lipid material accumulates in deposits underneath the retinal pigment epithelium. These deposits are known as drusen, and can be seen as pale yellow spots on the retina.

The pigment of the retinal pigment epithelium may become disturbed, with areas of hyperpigmentation and hypopigmentation. In the later stages of the disease, the retinal pigment epithelium may atrophy completely. This loss can occur in small focal areas or can be widespread (geographic atrophy).

Wet AMD

In some cases, new blood vessels grow under the retinal pigment epithelium and occasionally into the subretinal space (exudative or neovascular AMD, or “wet AMD”). Haemorrhage can occur which often results in increased scarring of the retina. The early stages of the disease are in general asymptomatic. In the later stages there may be considerable distortion within the central visual field leading to a complete loss of central visual function.

Some people with dry AMD go on to develop wet AMD. In wet AMD, abnormal blood vessels grow into the macula and leak blood or fluid which leads to scarring of the macula and rapid loss of central vision.

Risk factors

The major risk factors for AMD are age, genetic factors and tobacco smoking. AMD usually affects people over 60, but can occur earlier. Considerable research has focussed on the role of diet, light exposure and association with cardiovascular disease and its risk factors, however, the effects of these risk factors are less certain.

Impact

AMD is the third most common cause of blindness in the world and the leading cause of blindness in higher income countries with ageing populations.

Approximately 5% of blindness globally is due to AMD. It is estimated that globally 196 million people have AMD in 2020, increasing to 288 million in 2040.

Treatment and successes

Currently there is no effective treatment for dry AMD. There is some evidence that antioxidant vitamin supplements may slow down the progression of AMD to late stage disease and visual loss.

Treatment of AMD has been revolutionised by the use of anti-vascular endothelial growth factor agents that bind to vascular endothelial growth factor or their receptors and slow down the growth of new blood vessels. These interventions are delivered by injection into the eye. However, they are expensive and are only applicable for the neovascular form of the disease.

 

Photo Credits

Rachael Ferguson