Age Related Macular Degeneration
Dr Raja Narayanan, Consultant, Centre for Vitreo Retinal Diseases,
L V Prasad Eye Institute
Age-Related Macular Degeneration (AMD) is the leading cause of blindness in individuals over the age of 50 in the developed countries. Early manifestations of AMD include focal drusens - the yellow deposits under the retina associated with minor visual complaints. But the later stages of the disease result in severe vision loss.
The non-exudative or dry form of AMD is approximately 10 times more prevalent than the exudative or wet form of AMD, though the latter is the leading cause of blindness from AMD. Age is the most important risk factor for AMD. However, studies indicate genetic and environmental influences for AMD, with smoking being an important risk factor. Also, high cholesterol, hypertension, light exposure, light iris color have been suggested to have a possible association with AMD.
In the dry form of AMD, visual loss is gradual as opposed to the wet form of the disease in which there is usually a sudden visual loss. The complaints of patients with wet AMD may vary from distorted vision, central or paracentral black spots, to a sudden, nonspecific reduction in central vision. CNV or Choroidal neovascularization is the creation of new blood vessels in the choroid layer of the eye, and is a common symptom of wet AMD.
However, not all patients with CNV will manifest other symptoms of AMD. Therefore, even asymptomatic patients over 50 years of age with large, soft confluent drusen, and who have risk factors for CNV, should be periodically examined for signs of CNV development. A simple test for daily monitoring of vision in patients with AMD is the Amsler grid. It tests the central 10 degrees of visual field around the fixation, with each box on the grid representing one degree of visual field. If a patient notices distorted, missing areas, or black spots, then they should schedule an appointment with an ophthalmologist immediately.
Treatment of dry AMD
Nutritional supplements: Various trials have looked at the possibility of preventing AMD by nutritional supplementation with antioxidants because of the importance of free radicals in the pathogenesis of AMD. The Age Related Eye Disease Study (AREDS) data suggest that patients may reduce the risk of developing complications of AMD by taking daily nutritional supplements containing zinc and other antioxidants. Lutein and zeaxanthin are the two major antioxidant micronutrients found in the human retina. These micronutrients protect against AMD by absorbing light and quenching the free radicals, and the best natural food sources for these are green leafy vegetables and other green or yellow vegetables.
Treatment of wet AMD
Photodynamic therapy (PDT): In PDT, tissues treated with photosensitizers are exposed to low intensity laser exposure to produce a photochemical effect. It causes selective destruction of CNV with preservation of the overlying neurosensory retina. However, PDT treatment does not result in improvement in vision though it slows the progression of the disease.
Pharmacologic intervention: Pharmacotherapy not only avoids laser-induced damage to the overlying retina but also has been shown to improve vision significantly in many cases. At present, numerous drugs are available in the market and some are in the pipeline waiting for regulatory approval. The disadvantages of these intraocular injections are that the patient has to come frequently to the clinic for a checkup and most of them need multiple injections in the eye on a regular basis.
Future treatments in the horizon for AMD such as retinal pigment epithelium (RPE) and photoreceptor transplantation, gene therapy, and retinal implants provide hope for a long lasting solution for this blinding disease.
Low vision aids: In those patients whose eyes are in the last stage of the disease with no treatment available, low vision aids may help. These include appropriate lenses, magnifying aids (optical or electronic) and proper encouragement to the patient to use these. The L V Prasad Eye Institute has a world renowned Low Vision Aids department where many patients with advanced eye disease have benefited.
Figure: Abnormal blood vessels are seen with surrounding blood in the central retina in this patient of wet AMD.