July 16, 2012 Macular degeneration is a disease of the central part of the retina called the macula, which usually occurs in older adults, which results in loss of sight in the center of the visual field. It occurs in two forms: “dry” and “wet”. Macular degeneration is the leading cause of blindness in people older than 50 years. This disease can make it difficult or even disable the ability of reading and recognizing faces, even though the remaining peripheral vision enables the patient to do other daily activities.
Although some macular dystrophies that affect young people are sometimes associated with macular degeneration, the term “macular degeneration” generally refers only to senile macular degeneration.
Senile macular degeneration begins with characteristic yellow deposits in the macula (the central area of the retina that allows visual acuity) called druses between the lower layer of the choroid. This phase of the early changes is called senile maculopathy. Most people with these early changes have good visual acuity. For some people, however, senile maculopathy progresses to age-related macular degeneration. The risk of progression is significantly higher when druses are larger and numerous, and when they are associated with changes in the retinal pigment epithelium beneath the macula. Recent studies indicate that large and soft druses are associated with hypercholesterolemia, and that they may respond to medications that lower blood cholesterol levels.
Causes:
The retina is the inner layer of the eye, and it contains nerve cells and nerve fibers that enable the eyesight. Behind the retina is the choroid, the middle layer of the eye that contains blood vessels that participate in feeding the retina. In dry (non-exudative) form of macular degeneration, the cellular remnants aka druses accumulate between the retina and choroid, which causes retina to detach from its substrate, retinal pigment epithelium. In the wet (exudative) form, which is more severe, blood vessels grow from the choroid, and may also cause retinal detachment from its substrate.
The cause of this disease is unknown, but the risk factors identified so far are age, heritage, hypertension, hypercholesterolemia, obesity and smoking.
Types:
Advanced senile macular degeneration, which is responsible for severe vision loss, but never for complete blindness, has two forms: dry and wet.
Central geographic atrophy, “dry” form of advanced age-related macular degeneration, occurs as a result of atrophy of the retinal pigment epithelium, which in turn causes the loss of photoreceptors (rods and cones) in the central parts of the retina, and consequently decreases in visual acuity. Currently there is no effective treatment for central geographic atrophy. Some studies show that a combination of high doses of vitamins and antioxidants lutein and zeaxanthin, slow down the progression of dry age-related macular degeneration.
Dry form Wet form
Neovascular or exudative senile macular degeneration, “wet” form of advanced AMD, causes vision loss due to abnormal blood vessels that grow out of choriocapillaris breaking the Bruch’s membrane, causing bleeding and accumulation of fluid and protein under the macula. If this condition is left untreated, bleeding, fluid and protein accumulation, and scarring as a result of the growth of blood vessels, eventually causes permanent and irreparable damage to the photoreceptors, and rapid loss of visual acuity.
Wet form represents 88% of cases of blindness caused by senile macular degeneration. Wet form is always evolving from the dry form.
Symptoms:
Blurred vision of patients with non-exudative macular degeneration may be asymptomatic or they may notice a gradient loss of central vision, while those with exudative macular degeneration often notice the rapid appearance of vision loss; central scotoma (shadows or areas with a lack of vision), distorted vision (metamorphopsia) – grid with straight lines appear wavy and parts of the grid may appear white (patients often notice it by looking at the mini-blinds in their house); problem of distinguishing colors, especially dark from dark colors and light from light colors, slow recovery of visual function after exposure to bright light, loss of contrast sensitivity.
Normal vision Vision of a patient suffering from macular degeneration
Stains changes, pigment changes, exudative changes: bleeding in the eye, severe exudation, subretinal / sub-RPE (ie, below the retinal pigment epithelium) / intraretinal fluid; atrophy: beginning and geographical, visual acuity drastically decreasing (two levels or more) from: 20/20 to 20/80.
Treatment:
Until recently there was no effective treatment of wet form of age-related macular degeneration. However, new drugs, called anti-angiogenic or anti-VEGF (anti- Vascular Endotheilal Growth Factor) agents, can cause regression of abnormal blood vessels and improve vision when injected in the vitreous of the eye. Injections can be moderately painful and usually require several repetitions in one month apart. Currently on the market are ranibizumab (Lucentis), bevacizumab (Avastin) and pegaptanib (Macugen). Only Lucentis and Macugen are approved by FDA (Food and Drug Administration) since April 2007. In
Amsler’s test is one of the simplest and most effective methods for patients to monitor the health of the yellow spot (macula). Amsler’s web is a square grid pattern with lines and a black dot in the center. The central black dot is used for fixation (i.e., as a place to which the respondent looks). When looking at a central black dot, in people with normal sight, lines all around the black spot look straight and evenly arranged, without redundant or deficient areas. For persons with the eye spot affected by the disease, as in macular degeneration, the lines can look bent, distorted and / or missing. Macular degeneration alone does not lead to complete blindness, and in almost all cases remains at least some vision. That is because the area of yellow spot affects about 5% of the retina and is responsible for approximately 35% of the visual field. The remaining 65% (peripheral visual field) remains unaffected by the disease. Loss of central vision significantly affects visual function. For example, without central vision it is not possible to read. Pictures of the loss of central vision in macular degeneration that are illustrated with black spots are not accurate and do not give the right idea about the type of vision loss. This may be proved by writing letters 15 cm high on a piece of paper and give the patient to try to identify them looking straight ahead while holding the paper slightly to the side. For most people, this is surprisingly difficult to do. There is a loss of feeling for contrast so that the outlines, the shadows and the colors are less vibrant. Loss of sense of contrast can be easily measured on the contrast sensitivity test. Similar symptoms with a lot of different etiology and different treatment may be caused by epiretinal membrane, macular fold (macular pucker) or rupture of blood vessels in the eye.
