cross-sectional view. Courtesy
NIH National Eye Institute ]]
National Eye Institute ]]
is a medical condition where the light sensing cells in the condition. These forms are sometimes called Juvenile macular degeneration (JMD). In macular degeneration the final form results in missing or blurred vision in the central, reading part of vision. The outer, peripheral part of the vision remains intact.
ARMD is further divided into a "dry," or nonexudative, form and a "wet," or exudative, form. Eighty five to ninety percent of cases are categorized as "dry" macular degeneration where fatty tissue, known as drusen, will slowly build up behind the
Retina . Ten to fifteen percent of cases involve the growth of abnormal blood vessels under the retina. These cases are called "wet" macular degeneration due to the leakage of blood and other fluid from behind the retina into the eye. Wet macular degeneration usually begins as the dry form. If allowed to continue without treatment it will completely destroy the macula. Medical,
Photodynamic , laser photocoagulation and laser treatment of wet macular degeneration are available.
- Approximately 10% of patients 66 to 74 years of age will have findings of macular degeneration. The prevalence increases to 30% in patients 75 to 85 years of age.
- The only environmental exposure clearly associated with macular degeneration is Tobacco Smoking {Link without Title} .
- The lifetime risk of developing late-stage macular degeneration is 50% for people who have a relative with macular degeneration vs. 12% for people who do not have relatives with macular degeneration, i.e. a four fold higher risk.
- Complement factor H (CFH) and complement factor B (CFB) genes have been determined to be strongly associated with a person's risk for developing macular degeneration. It is not yet clear what initiates the immune response against retina, although this might involve a humoral immune response.
- : Also known as High Blood Pressure .
- - high cholesterol, Obesity .
- is associated with an increased risk of macular degeneration in both women and men. Fat provides about 42 % of the Food Energy in the average American diet. A diet that derives closer to 20-25 % of total food energy from fat is probably healthier. Reducing fat intake to this level means cutting down greatly on consumption of red meats and dairy products such as milk, cheese, and butter. Eating more cold-water fish (at least twice weekly), rather than red meats and eating any type of nuts may help macular degeneration patients.(Reference: Macular degeneration Types and Risk Factors .
- It has been proposed that age related accumulation of low molecular weight, phototoxic, pro-oxidant Melanin oligomers within lysosomes in the retinal pigment epithelium (RPE) may be partly responsible for decreasing the digestive rate of photoreceptor outer rod segments (POS) by the RPE. A decrease in the digestive rate of POS has been shown to be associated with Lipofuscin formation - a classic sign associated with macular degeneration. (Reference: Ophthalmic Research, 2005; volume 37: pages 136-141. "Melanin aggregation and polymerization: possible implications in age related macular degeneration")
- Macular degeneration is more likely to be found in whites than in blacks {Link without Title} {Link without Title} .
- especially blue light. There is conflicting evidence as to whether exposure to sunlight contributes to the development of macular degeneration. A recent study in the ''British Journal of Opthalmology'' on 446 subjects found that it does notKhan JC, Shahid H, Thurlby DA, Bradley M, Clayton DG, Moore AT, Bird AC, Yates JR; Genetic Factors in AMD Study. "Age related macular degeneration and sun exposure, iris colour, and skin sensitivity to sunlight." ''Br J Ophthalmol.'' 2006 Jan;90(1):29-32.. High Energy Visible Light (HEV) has been implicated as a cause of age-related macular degenerationGlazer-Hockstein C, Dunaief JL. "Could blue light-blocking lenses decrease the risk of age-related macular degeneration?" ''Retina.'' 2006 Jan;26(1):1-4. PMID 16395131Margrain TH, Boulton M, Marshall J, Sliney DH. "Do blue light filters confer protection against age-related macular degeneration?" ''Prog Retin Eye Res.'' 2004 Sep;23(5):523-31. PMID 15302349.
- Drusen
- Pigmentary alterations
- Exudative changes: hemorrhages, 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.
- 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.
- 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 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, the lines can look bent, distorted and/or missing.
The traditional Amsler grid test is a black and white pattern that may miss early defects (references at
www.ixm.us ). Since treatment and vision preservation in macular degeneration is facilitated by early detection of the disease, a more sensitive blue-on-yellow Amsler grid test pattern has recently been introduced (
IXMUS Home Test ).
'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 effects 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 devasting 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.
Fluorescein Angiography allows for the identification and localization of abnormal vascular processes.
During the early stages of the disease, the neural layers of the retina remain relatively unaffected. This fact makes it a possible target for treatment with a retinal prosthesis, which are currently under development.
Several macular degeneration clinical trials are currently underway. The most promising approach is the anti- (Lucentis),
Anecortave (Retaane),
Bevacizumab (Avastin),
Squalamine (Evizon) and
SiRNA . Second generation antisense oligonucleotides
ICo-007 targeting the Raf-1 kinase are also under investigation as a target for broad inhibition of multiple pro-angiogenic signals. The most promising of these treatments,
Ranibizumab (Lucentis), is the 1st drug tested that has shown significant improvement in visual acuity in multiple phase III trials. Radiation therapy (
Brachytherapy ) and
Rheopheresis are also being evaluated for wet macular degeneration
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Recent studies suggest that
Statin s, a family of drugs used for reducing
Cholesterol levels, may be effective in prevention of AMD, and in slowing its progression
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The
Age-Related Eye Disease Study concluded that high levels of
Antioxidant s and
Zinc can reduce some people's risk of developing advanced AMD by about 25 percent.
"Macular degeneration" is a descriptive term for any condition which leads to loss of function of the light sensitive cells at the center of the retina. Several rare hereditary conditions can lead to macular degeneration in children and adolescents. These include:
