Age-related macular degeneration (AMD) is the leading cause of blindness in people over the age of 60 in the western world. About 25% of over 60s in the UK have some degree of visual loss due to AMD. This figure is expected to triple within the next 10-20 years.
AMD is a disease associated with aging that gradually destroys sharp, central vision. Central vision is needed for seeing objects clearly and for common daily tasks such as reading and driving.
The retina is a very thin tissue that lines the back of the eye and contains the light-sensing cells that send visual signals to the brain. Sharp, clear central vision is processed by the macula (also sometimes called the fovea) which is a circular patch in the central part of the retina and is about the size of a grain of barley.
AMD occurs in two forms: dry and wet.
Dry AMD occurs when the light-sensitive cells in the macula slowly break down, gradually blurring central vision in the affected eye. As dry AMD gets worse, patients may see a blurred spot in the center of their vision. Over time, as less of the macula functions, central vision is gradually lost in the affected eye.
The most common symptom of dry AMD is slightly blurred vision. Patients may have difficulty recognizing faces or may need more light for reading and other tasks. Dry AMD generally affects both eyes, but vision can be lost in one eye while the other eye seems unaffected.
One of the most common early signs of dry AMD is drusen.
Wet AMD occurs when abnormal blood vessels behind the retina start to grow under the macula. These new blood vessels tend to be very fragile and often leak blood and fluid. The blood and fluid raise the macula from its normal place at the back of the eye. Damage to the macula occurs rapidly.
With wet AMD, loss of central vision can occur quickly. Wet AMD is also known as advanced AMD. It does not have stages like dry AMD.
An early symptom of wet AMD is that straight lines appear wavy.
AMD is associated with defects of the retinal support cells – the retinal pigment epithelial cells (RPE). The rods and cones (the photoreceptors) in the retina, which are the light sensitive cells, depend for their survival on the normal functioning of these cells, and so failure of these cells leads to progressive loss of vision. To make matters worse, the disease often provokes a scarring process at the back of the eye leading to the formation of new blood vessels within the retina which subsequently leak fluid resulting in exudative AMD or so called “wet” AMD.