Age-related Macular Degeneration
Age-related Macular Degeneration (AMD) is the leading cause of irreversible blindness in the developed world. The primary cause is thought to be the premature dysfunction of the retinal pigment epithelium (RPE), a monolayer responsible for most of the maintenance functions of the neurosensory retina. The early stages manifest themselves by the development of drusen and hyper-pigmentation or hypo-pigmentation of the RPE. Patients at the later stage usually suffer from severe loss of visions and signs of choroidal neovascularization, sub-retinal hemorrhage, or geographic atrophy.
There are essentially two categories of AMD: namely, wet (exudative), and dry (non-exudative). The dry form is more common. Dry AMD manifests itself clinically as formation of drusen and geographic atrophy of the RPE. Drusen are produced by the deposition of lipofuscin (a retinal waste product) and by RPE separation from its underlying basement membrane. This process results from an accelerated ageing of the RPE, and accounts for approximately 10% of the cases of severe visual loss seen caused by AMD.
Approximately 10% of patients with AMD suffer from its wet form. Wet or exudative AMD is a secondary complication in which abnormal choroidal neovascularization breaches the weakened RPE, causing retinal edema, sub-retinal serous exudation, and eventual scarring of the overlying retina. Damage to the macula occurs very rapidly, as does loss of central vision.
Researchers have set forth several theories on the causes of AMD, including primary RPE and Bruch membrane senescence, ocular perfusion abnormalities, genetic defects, and oxidative insults.
Finally, small number of native macular pigments lutein and zeaxanthin has been hypothesized to contribute to AMD development. These pigments are thought to play a protective role by limiting oxidative insults or by filtering out harmful wavelengths of light. It is a degenerative condition caused by vascular abnormalities that deprive the sensitive retinal tissue of oxygen and nutrients, and prevent the removal of the waste products of retinal cellular metabolism.
Incidence and Prevalence
AMD is the most prevalent form of macular disease in older persons and the leading cause of blindness in individuals over age 50 in industrialized countries.
15% of individuals with non-exudative AMD develop vision loss.
10-20% of patients with non-exudative AMD progress to the exudative form.
85% of exudative cases develop vision loss.
Risk factors consistently identified in studies are advancing age, a family history of AMD, and smoking.
For more about AMD see:
http://www.amd.org/what-is-amd
www.heidelbergengineering.com/clinical-applications/retina-clinical-applications/
http://www.alcon.com/en/eye-health/macular-degeneration.asp
http://www.bluepeakexperience.com/home.html
