Dry Macular Degeneration

 

Macular degeneration, also known as age-related macular degeneration (AMD or ARMD), is a medical condition which may result in blurred or no vision in the center of the visual field. Early on there are often no symptoms. Over time, however, some people experience a gradual worsening of vision that may affect one or both eyes. While it does not result in complete blindness, loss of central vision can make it hard to recognize faces, drive, read, or perform other activities of daily life. Visual hallucinations may also occur and these do not represent a mental illness.

Macular degeneration typically occurs in older people. Genetic factors and smoking also play a role. It is due to damage to the macula of the retina. Diagnosis is by a complete eye exam. The severity is divided into early, intermediate, and late types. The late type is additionally divided into “dry” and “wet” forms with the dry form making up 90% of cases.

Prevention includes exercising, eating well, and not smoking. Antioxidant vitamins and minerals do not appear to be useful for prevention. There is no cure or treatment that returns vision already lost. In the wet form, anti-VEGF medication injected into the eye or less commonly laser coagulation or photodynamic therapy may slow worsening. Supplements in those who already have the disease may slow progression.

In 2015 it affected 6.2 million people globally. In 2013 it was the fourth most common cause of blindness after cataracts, preterm birth, and glaucoma. It most commonly occurs in people over the age of fifty and in the United States is the most common cause of vision loss in this age group. About 0.4% of people between 50 and 60 have the disease, while it occurs in 0.7% of people 60 to 70, 2.3% of those 70 to 80, and nearly 12% of people over 80 years old.

Signs and Symptoms
Signs and symptoms of macular degeneration include:

Visual symptoms
Distorted vision in the form of metamorphopsia, in which a grid of straight lines appears wavy and parts of the grid may appear blank: Patients often first notice this when looking at things like miniblinds in their home or telephone poles while driving. There may also be central scotomas, shadows or missing areas of vision
Slow recovery of visual function after exposure to bright light (photostress test)
Visual acuity drastically decreasing (two levels or more), e.g.: 20/20 to 20/80
Blurred vision: Those with nonexudative macular degeneration may be asymptomatic or notice a gradual loss of central vision, whereas those with exudative macular degeneration often notice a rapid onset of vision loss (often caused by leakage and bleeding of abnormal blood vessels).
Trouble discerning colors, specifically dark ones from dark ones and light ones from light ones
A loss in contrast sensitivity
Macular degeneration by itself will not lead to total blindness. For that matter, only a small number of people with visual impairment are totally blind. In almost all cases, some vision remains, mainly peripheral. Other complicating conditions may lead to such an acute condition (severe stroke or trauma, untreated glaucoma, etc.), but few macular degeneration patients experience total visual loss.

The area of the macula comprises only about 2.1% of the retina, and the remaining 97.9% (the peripheral field) remains unaffected by the disease. Even though the macula provides such a small fraction of the visual field, almost half of the visual cortex is devoted to processing macular information.

The loss of central vision profoundly affects visual functioning. It is quite difficult, for example, to read without central vision. Pictures that attempt to depict the central visual loss of macular degeneration with a black spot do not do justice to the devastating nature of the visual loss. This can be demonstrated by printing letters six 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 difficult to do.

Epidemiology
Age-related macular degeneration accounts for more than 54% of all vision loss in the white population in the USA. An estimated 8 million Americans are affected with early age-related macular degeneration, of whom over 1 million will develop advanced age-related macular degeneration within the next 5 years. In the UK, age-related macular degeneration is the cause of blindness in almost 42% of those who go blind aged 65–74 years, almost two-thirds of those aged 75–84 years, and almost three-quarters of those aged 85 years or older.

Macular degeneration is more likely to be found in Caucasians than in people of African descent.

Research directions
Association with other age-related diseases
Studies indicate drusen associated with AMD are similar in molecular composition to Beta-Amyloid (βA) plaques and deposits in other age-related diseases such as Alzheimer’s disease and atherosclerosis. This suggests that similar pathways may be involved in the etiologies of AMD and other age-related diseases.

Genetic testing
A practical application of AMD-associated genetic markers is in the prediction of progression of AMD from early stages of the disease to neovascularization.

Stem cell transplant
Cell based therapies using bone marrow stem cells as well as retinal pigment epithelial transplantation are being studied. A number of trials have occurred in humans with encouraging results.

Other types
There are a few other (rare) kinds of macular degeneration with similar symptoms but unrelated in etiology to Wet or Dry age-related macular degeneration. They are all genetic disorders that may occur in childhood or middle age.

Best’s disease
Sorsby’s fundus dystrophy is an autosomal dominant, retinal disease characterized by sudden acuity loss resulting from untreatable submacular neovascularisation
Stargardt’s disease (juvenile macular degeneration, STGD) is an autosomal recessive retinal disorder characterized by juvenile-onset macular dystrophy, alterations of the peripheral retina, and subretinal deposition of lipofuscin-like material.
Similar symptoms with a very different etiology and different treatment can be caused by epiretinal membrane or macular pucker or any other condition affecting the macula, such as central serous retinopathy.

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