Macular Degeneration or Age-related Macular Degeneration (AMD) is the leading cause of central vision loss in people 60 years or older.
The retina is the lining at the back of the eye. Along with the optic nerve, it forms the ‘nerve’ of the eye. A healthy retina is essential for normal vision. The retina is a complex structure, made up of ten different layers. The most important are two – the retinal pigment epithelium (RPE) and the photoreceptors (rods and cones). A healthy RPE is essential for the normal functioning of the retina. Rods generally help with night vision while cones help with day vision and colour vision. The central retina is called the macula; this area is very rich in cones and a healthy macula is essential to be able to read fine print, identify colours, faces and so on.
With age, the RPE becomes less efficient, leading to the formation of ‘Drusen’, which is a hallmark of AMD. AMD affects the macular region of the retina, leading to loss of central vision. It accounts for 8.7% of all blindness worldwide and is the most common cause of blindness in people older than 60 years. It is estimated that about 1.5 Cr to 4 Cr people in India suffer from AMD. AMD can have a profound impact on quality of life and independence. Affected individuals may be unable to read, write, and drive due to their loss of central vision. The greatest risk factors for AMD are ageing and smoking. Excessive exposure to sunlight and an unhealthy diet may increase the risk. Genetics also plays a role in AMD; this is however not routinely tested in people at risk.
There are two types of AMD-dry (Atrophic) and wet (Exudative). Dry AMD constitutes about 85% of the cases and is characterized by yellow subretinal deposits called drusen. The advanced form of dry AMD is called ‘Geographic atrophy’. In wet AMD, abnormal blood vessels grow under the retina that then leak blood and other fluids. Although more serious, and faster to progress, wet AMD can be treated with injections of Anti VEGF (vascular endothelial growth factor) into the cavity (vitreous) of the eye. There is currently no known therapy for dry AMD.
One of the ways that scientists are addressing treatment for dry AMD is to replace the diseased RPE with healthy cells. Organizations like Eyestem (www.eyestem.com) are aimed at doing precisely this. The process involves obtaining peripheral blood from healthy donors and converting them into RPE cells. These cells will then be injected under the retina, in the subretinal space in place of the lost RPE as a means to halt the progression of dry AMD. However, this treatment is still in the experiment stage.
The National Eye Institute, USA conducted a landmark study called the Age-Related Eye Disease Study (AREDS) for the treatment of AMD. It showed that a specific antioxidant supplementation can slow the progression of AMD. The AREDS2 formulation, which is available as several over-the-counter supplements in India is recommended for patients with both dry and wet AMD. Use of appropriate low visual aids helps significantly in AMD.