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What happens in the brain?

While the eye detects and encodes the visual information, the brain is ultimately responsible for most of the processing and for making sense of it.

In particular, a large region of the visual cortex is concerned with analysing the information from a small area of the central visual field.  As a result of the loss of photoreceptors resulting from Age-related macular degeneration (AMD), there is initially a reduction in the visual information reaching the brain originating from this area and, subsequently, visual function degenerates. As the disease progresses, no information from this area reaches the brain and visual perception here is lost.

It is currently an active area of research to find out what happens to the visual regions of the brain lacking their normal input. Animal studies have shown that although regions of the early visual cortex lacking its normal visual input become silent, they can still be responsive after some time. A recent study in advanced AMD patients has shown that visual stimulation on spared peripheral visual areas can elicit a response in an otherwise silent region. However, what is the extent of this plasticity? Would it be beneficial or detrimental to the subject’s vision? Is it reversible? These issues are important in order to decide which strategies to preserve vision are most adequate, when they should be attempted to obtain optimal results and, ultimately, what their limitations are.