Age-Related Macular Degeneration (AMD) is a condition in which the centre of the retina (the macula) gradually deteriorates, and the detailed vision needed for reading, driving and recognizing faces is lost. There are two types of AMD, a dry form and a wet form: the dry form is more common, but less severe, than the wet form. In the dry form, the cells don’t take in enough vital nutrients and fail to clear cellular by-products so that eventually photoreceptors are lost from the central part of the eye. The wet form is characterised by the growth of new blood vessels which can bleed and leak fluid, leading to scarring and more rapid loss of vision. There is currently no specific treatment for dry AMD, whilst treatment for the wet form involves laser treatment to seal the leaking blood vessels or injection of anti-vascular endothelial growth factor (anti-VEGF) drugs directly into the eye.
A report in the New England Journal of Medicine now warns that a new treatment being developed for the treatment of wet AMD may actually cause harm in patients with the dry form of the disease. The new treatment, which is currently undergoing clinical trials, uses interfering RNA (RNAi) technology to downregulate production of VEGF or VEGF receptors. The new study identifies a link between toll-like receptor 3 (TLR3), which helps the immune system to recognize viral infections, and dry AMD. A mutation associated with low activity of TLR3 appears to offer protection against dry AMD, possibly by suppressing death of retinal cells. The use of RNAi induces TLR3 activation, and so could worsen the prognosis in patients with dry AMD. The discovery also suggests that TLR3 inhibitors may offer a potential new treatment for the more common, dry, form of AMD.