2 Clinical need and practice
2.1 Age-related macular degeneration (AMD) is an eye condition that leads to a progressive loss of central vision. People retain some peripheral vision, but the ability to see well enough to recognise faces, drive and read is affected, and vision can deteriorate rapidly.
2.2 AMD occurs in two forms, dry and wet AMD. Dry AMD (non-neovascular) is a form of extensive atrophy (wasting) of cells that progresses slowly, whereas the wet form can lead to a rapid worsening of vision. Wet (neovascular) AMD is characterised by the development of immature blood vessels that grow between the retinal pigment epithelial cells and the photoreceptor cells in the centre of the retina, a process known as choroidal neovascularisation (CNV). These vessels easily haemorrhage and cause lesions on the macula, leading to visual impairment. A protein known as vascular endothelial growth factor (VEGF), which induces new blood vessel formation (angiogenesis), vascular permeability and inflammation, has been implicated in the development and progression of CNV. CNV can be subdivided into classic and occult forms according to its appearance on investigation by fluorescein angiography. A mixture of classic and occult CNV can occur in the same lesion. CNV can also be described in terms of its location: the fovea is the central part of the macula, and CNV that develops below the foveal area is termed 'subfoveal CNV'.
2.3 There are about 26,000 new cases of wet AMD in the UK each year and the condition affects more women than men. The condition usually affects people who are over 50 years old and the risk increases significantly with age. The most commonly cited risk factor for AMD is cigarette smoking; the risk of developing AMD is 3.6 times greater for current and former smokers than for people who have never smoked.
2.4 Patient management consists of social support, visual rehabilitation and the provision of aids to help with low vision. However, in the 20% of patients with classic no occult subfoveal CNV and a best-corrected visual acuity of 6/60 or better, photodynamic therapy (PDT) is an option. Visual acuity of 6/60 means that the patient can only see from a distance of 6 metres or less what someone with normal vision can see from 60 metres away. PDT involves injecting verteporfin, a photosensitive drug that remains in the new blood vessels in the eye. This is followed by treatment with a low-powered laser, which activates the drug causing cell death. The aim is to destroy the CNV lesions without damaging the retina, thereby halting or reducing progressive loss of vision. PDT does not prevent new vessels forming: it only treats established pathological vessels. More recently, drugs that inhibit the action of VEGF have been developed for the treatment of wet AMD.