Macular degeneration, also known as age-related macular degeneration (AMD or ARMD), is a medical condition which results in blurred (or absent) vision in the centre of the visual field. It can affect one or both eyes.

It's characterised by a general degeneration of the eye's central photo-receptors (retina) and surrounding tissues. Some types develop over a number of years, others in a matter of weeks.

It's estimated that it affects more than 6 million people worldwide - and it's a leading cause of vision loss in people 50 years or older. Autopsy research has shown that around a third of people over 65 have some degree of AMD.

The factors which trigger the development of the disease are not known, but there may be genetic links. Exposure to toxins etc (e.g. smoking), nutritional factors, and cardiovascular disease are also under consideration. Oxidative stress, hypertension, obesity, and atherosclerosis may also be factors.

Currently, the etiology of AMD remains elusive. In addition to age, recognized risk factors include cigarette smoking and diet.
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Among all identified potential environmental factors, only age, diet and smoking are agreed upon by all to increase the risk of AMD.

Source : Genetic factors of age-related macular degeneration ^{[ Paywalled ]} Progress in Retinal and Eye Research, Volume 23, Issue 2, Pages 229-249

It is a permanent condition. There are various injected-drug treatment options - some at the experimental stage - which can slow the progress of some types of the disease, but most of the drugs work by inhibiting blood vessel development, and are not without possible side effects (example ref.).

For further technical details of AMD see :

Clinical Interventions in Aging 2017; 12: and :

The Macular Society