Macular Degeneration Disease is a medical condition predominantly found in elderly adults in which the center of the inner lining of the eye, known as the macula area of the retina, suffers thinning, atrophy, and in some cases bleeding.
This can result in loss of central vision, which entails inability to see fine details, to read, or to recognize faces. According to the American Academy of Ophthalmology, it is the leading cause of central vision loss (blindness) and in the United States today for those over the age of fifty years.
Although some macular dystrophies that affect younger individuals are sometimes referred to as Macular Degeneration Disease, the term generally refers to age-related macular degeneration (AMD or ARMD).
Age-related Macular Degeneration Disease begins with characteristic yellow deposits in the macula (central area of the retina) called drusen. Most people with these early changes have good vision. People with drusen can go on to develop advanced Macular Degeneration Disease. The risk is considerably higher when the drusen are large and numerous and associated with disturbance in the pigmented cell layer under the macula. Recent research suggests that large and soft drusen are related to elevated cholesterol deposits and may respond to cholesterol lowering agents or the Rheo Procedure.
Advanced Macular Degeneration Disease, which is responsible for profound vision loss, has two forms: dry and wet. Central geographic atrophy, the dry form of advanced Macular Degeneration Disease, results from atrophy to the retinal pigment epithelial layer below the retina, which causes vision loss through loss of photoreceptors (rods and cones) in the central part of the eye. While no treatment is available for this condition, vitamin supplements with high doses of antioxidants, Lutein and Zeaxanthin, have been demonstrated by the National Eye Institute and others to slow the progression of dry macular degeneration and in some patients, improve visual acuity.
Neovascular or exudative AMD, the wet form of advanced AMD, causes vision loss due to abnormal blood vessel growth in the choriocapillaries, through Bruch's membrane, ultimately leading to blood and protein leakage below the macula. Bleeding, leaking, and scarring from these blood vessels eventually cause irreversible damage to the photoreceptors and rapid vision loss if left untreated.
Until recently, no effective treatments were known for wet macular degeneration. However, new drugs, called anti-VEGF (anti-Vascular Endothelial Growth Factor) agents, when injected directly into the vitreous humor of the eye using a small, painless needle, can cause contraction of the abnormal blood vessels and improvement of vision. The injections frequently have to be repeated on a monthly or bi-monthly basis. Examples of these agents include Lucentis, Avastin and Macugen. Only Lucentis and Macugen are FDA approved as of April 2007, and only Lucentis and Avastin appear to be able to improve vision, but the improvements are slight and do not restore full vision.
Where is the macula:
The macula is located in the center of the retina, the light-sensitive tissue at the back of the eye. The retina instantly converts light, or an image, into electrical impulses.
The retina then sends these impulses, or nerve signals, to the brain.
Aging: Approximately 10% of patients 66 to 74 years of age will have findings of Macular Degeneration Disease. The prevalence increases to 30% in patients 75 to 85 years of age.
Smoking: The only environmental exposure clearly associated with Macular Degeneration Disease is tobacco smoking. Exposure to cigarette smoke more than doubles the risk of macular degeneration.
Family history: The lifetime risk of developing late-stage Macular Degeneration Disease is 50% for people who have a relative with macular degeneration vs. 12% for people who do not have relatives with macular degeneration.
Macular degeneration gene: The genes for the complement system proteins factor H (CFH) and factor B (CFB) have been determined to be strongly associated with a person's risk for developing Macular Degeneration Disease.
CFH is involved in inhibiting the inflammatory response mediated via C3b (and the Alternative Pathway of complement) both by acting as a cofactor for cleavage of C3b to its inactive form, C3bi, and by weakening the active complex that forms between C3b and factor B. C-reactive protein and polyanionic surface markers such as glycosaminoglycans normally enhance the ability of factor H to inhibit complement.
But the mutation in CFH(Tyr402His) reduces the affinity of CFH for CRP and probably also alters the ability of factor H to recognise specific glycosaminoglycans. This change results in reduced ability of CFH to regulate complement on critical surfaces such as the specialised membrane at the back of the eye and leads to increased inflammatory response within the macula.
High fat intake is associated with an increased risk of Macular Degeneration Disease in both women and men.
Oxidative stress: It has been proposed that age related accumulation of low molecular weight, phototoxic, pro-oxidant melanin oligomers within lysosomes in the retinal pigment epithelium may be partly responsible for decreasing the digestive rate of photoreceptor outer rod segments (POS) by the RPE.
Exposure to sunlight especially blue light. There is conflicting evidence as to whether exposure to sunlight contributes to the development of macular degeneration.
Signs of Macular Degeneration Disease:
Drusen
Pigmentary alterations
Exudative changes: hemorrhages in the eye, hard exudates, subretinal/sub-RPE/intraretinal fluid
Atrophy: incipient and geographic
Visual acuity drastically decreasing (two levels or more) ex: 20/20 to 20/80.
Symtoms
Blurred vision: Those with nonexudative macular degeneration may by asymptomatic or notice a gradual loss of central vision, whereas those with exudative macular degeneration often notice a rapid onset of vision loss.
Central scotomas (shadows or missing areas of vision)
Distorted vision (i.e. metamorphopsia) - A grid of straight lines appears wavy and parts of the grid may appear blank. Patients often first notice this when looking at mini-blinds in their home.
Trouble discerning colors; specifically dark ones from dark ones and light ones from light ones.
Slow recovery of visual function after exposure to bright light
The Amsler Grid Test is one of the simplest and most effective methods for patients to monitor the health of the macula. The Amsler Grid is essentially a pattern of intersecting lines (identical to graph paper) with a black dot in the middle. The central black dot is used for fixation (a place for the eye to stare at). With normal vision, all lines surrounding the black dot will look straight and evenly spaced with no missing or odd looking areas when fixating on the grid's central black dot.
When there is disease affecting the macula, as in Macular Degeneration Disease, the lines can look bent, distorted and/or missing.
'Vision loss' or 'blindness' in macular degeneration refers to the loss of 'central vision' only. The peripheral vision is preserved. Blindness in macular degeneration does not mean 'inability to see light' and even with far advanced macular degeneration, the peripheral retina allows for useful vision.
The loss of central vision profoundly affects visual functioning. It is not possible, for example, to read without central vision. Pictures which attempt to depict the central visual loss of macular degeneration with a black spot do not really do justice to the devastating nature of the visual loss. This can be demonstrated by printing letters 6 inches high on a piece of paper and attempting to identify them while looking straight ahead and holding the paper slightly to the side. Most people find this surprisingly difficult to do.
Similar symptoms with a very different etiology and different treatment can be caused by Epiretinal membrane or macular puckeror leaking blood vessels in the eye..
Fluorescein angiography allows for the identification and localization of abnormal vascular processes. Optical coherence tomography is now used by most ophthalmologists in the diagnosis and the followup evaluation of the response to treatment by using either Avastin or Lucentis which are injected into the vitreous of the eye at various intervals.
Prevention:
The Age-Related Eye Disease Study showed that a combination of high-dose beta-carotene, vitamin C, vitamin E, and zinc can reduce the risk of developing advanced AMD by about 25 percent in those patients who have earlier but significant forms of the disease.
This is the only proven intervention to decrease the risk of advanced Macular Degeneration Disease at this time.
Research cited in several of optometric journal articles identifies certain vitamins and minerals, known as antioxidants, that are effective in preventing cell destruction.
A follow up study, Age-Related Eye Disease Study 2 to study the potential benefits of lutein, zeaxanthine, and fish oil, is currently underway.
Anecortave acetate, (Retanne), is an anti-angiogenic drug that is given as an injection behind the eye (avoiding an injection directly into the eye) that is currently being studied as a potential way of reducing the risk of neovascular (or wet) AMD in high-risk patients.
Lutein:
One of over 600 known naturally occurring carotenoids.
Lutein was found to be present in a concentrated area of the macula, a small area of the retina responsible for central vision.
The hypothesis for the natural concentration is that lutein helps protect from oxidative stress and high-energy light.
Several studies show that an increase in macula pigmentation decreases the risk for eye diseases such as Age-related Macular Degeneration (AMD).
Zeaxanthin:
One of the two carotenoids contained within the retina.
Within the central macula, zeaxanthin is the dominant component.
There is epidemiological evidence of a relationship between low plasma concentrations of lutein and zeaxanthin on the one hand, and the risk of developing age-related macular degeneration (AMD) on the other.
Some studies support the view that supplemental lutein and/or zeaxanthin help protect against Macular Degeneration Disease.
Macular Degeneration Disease in its advanced forms, can result in legal blindness, resulting in a loss of driving privileges and an inability to read all but very large type. Perhaps the most grievous loss is the inability to see faces clearly or at all.
Some of these losses can be offset by the use of adaptive devices. A closed-circuit television reader can make reading possible, and specialized screen-reading computer software, e.g., JAWS for Windows, can give the blind person access to word processing, spreadsheet, financial, and e-mail access.
Current Research Into Macular Degeneration Disease:
There is currently enourmous amounts of research into Macular Degeneration Disease taking place around the world.
Some of this research includes:
Studying the possibility of transplanting healthy cells into a diseased retina.
Evaluating families with a history of AMD to understand genetic and hereditary factors that may cause the disease.
Looking at certain anti-inflammatory treatments for the wet form of AMD.
Research into nutrition and its effects on Macular Degeneration Disease.
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