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PostPosted: 26 Jun 2018 17:07 

Joined: 19 Dec 2017 14:21
Posts: 55
Age related macular degeneration (AMD) is the leading cause of severe vision loss among people aged 55 years and older. It results from damage to the macula, a small spot near the center of the retina (the back of the eye)and is responsible for good central vision.

The macula is the most sensitive part of the retina, and contains millions of photoreceptors or light sensing cells. When the macula is damaged, the central field of vision may appear distorted, hazy or dark

However, peripheral vision - the 'side' vision which is not focused remains unaffected and patients can still see enough to manage independently and recognize objects and persons until the advanced stages. To give an example persons with AMD may see the outline of the clock but cannot tell the time.

Facts about AMD
• AMD is the most common reason for loss of vision in older adults affective about 30 million persons globally
• It is of two types namely dry and wet AMD
• It is more common in women
• About 80-90% of persons have dry AMD
• Caucasian ethnicity is more commonly affected compared to Africans or Hispanics
• Wet AMD accounts for the majority cases of severe visual impairment in later stages of the disease

Risk factors of AMD

• The following factors increase the risk of development of AMD
• Increasing age
• Smoking history
• Family history of AMD – This suggests that genetic factors can play a role. Nearly 20 genes have been identified that are associated with an increased risk of developing AMD. Siblings of affected persons are four times more likely to develop AMD. The occurrence in identical twins is 50-100%
• Cardiac risk factors such as hypertension, hypercholesterolemia, obesity
• Cumulative damage to eye resulting from prolonged sunlight exposure
• Diet high in fat and foods having high glycemic index

Types of AMD
There are two types of AMD namely dry and wet.

Early or Dry AMD
Nearly 80% of persons suffer from “early” or “dry” AMD, which develops when there is accumulation of inadequately cleared waste material (drusen) under the macula and thinning of macular region of the retina. In this condition, vision is near normal or only mild visual impairment and may be incidentally detected during eye testing

Advanced or Wet AMD
A small proportion of patients with early (dry) AMD can progress to advanced or late AMD associated with severe visual impairment. Persons with large sized drusen have a greater risk of progressing to the wet form of AMD

The most common form of late AMD is “exudative” or “wet” AMD accounting for about 60% cases.
Wet AMD occurs due to growth of abnormal blood vessels under the retina. These abnormal vessels leak blood and fluid, which interfere with normal retinal function. Ultimately the bleeding and healing with scar formation results in severe permanent loss of central vision. However, the eye
does not become blind all at once as peripheral vision is intact

The less common form of late AMD termed geographic atrophy, where there is no accompanying abnormal vessel growth but severe thinning of the macula with resultant loss of vision

Classification of severity of AMD

The classification scheme developed by the 'Age-Related Eye Disease Study' (AREDS) trial has been found to be simple and useful to clinicians

• No AMD – Absence of very few drusen
• Early AMD - multiple small or a few intermediate drusen that may or may not be associated with abnormalities of retinal pigment epithelium (RPE)
• Intermediate AMD – several intermediate sized or one or more large drusen that may or may not be associated with geographical atrophy (GA) sparing the fovea
• Advanced AMD – GA affecting the fovea that may or may not be associated with features of wet AMD

Signs and symptoms of AMD
• Gradual and painless deterioration of vision despite usual glasses
• Needing brighter light to read as words appear hazy
• Colours appear dull and gray
• Reduced ability to discern objects and faces and facial expressions which appear dark
• Flickering or flashing lights (photopsia)
• In later stages, images are distorted, (for example patients report that straight lines appear wavy) with marked and rapid deterioration of vision
• Visual hallucinations (Charles Bonnet syndrome) – patients perceive different images than what is seen

Tests for AMD
In the early stages the patient may be asymptomatic and changes may be only detected by special tests
• Visual acuity test – The test chart assesses clarity of distant vision
• Dilated eye exam – After dilating the pupil with eye drops, the ophthalmologist looks at the back of the eye (retina) using a funduscope to look for characteristic changes
• Amsler grid – In AMD, reduced central vision may make the lines in the grid to disappear or seem wavy.
• Optical coherence tomography - The test gives precise information about the macula to distinguish between dry and wet form of AMD and to monitor response to treatment
• Fluorescein angiogram – A fluorescent dye is injected into the arm and images are captured as the dye passes through the blood vessels in the eye. This enables visualisation of leaking blood vessels, seen in late stages and rapidly progressive type of AMD.

Treatment of AMD
There is currently no treatment for dry form of AMD
Early AMD
Currently, early AMD has no treatment, which in many people is asymptomatic with no visual
impairment. Patients are usually advised periodic monitoring with retinal eye examination to
determine if the condition is advancing

Intermediate or late Dry AMD
Studies conducted by the National Eye Institute on the value of nutritional supplements in preventing or reducing progression of AMD - Age-Related Eye Disease Studies ((AREDS and AREDS2) have concluded that supplements containing the following ingredients may help persons with late AMD.

• 500 milligrams (mg) of vitamin C
• 400 international units of vitamin E
• 80 mg zinc as zinc oxide
• 2 mg copper as cupric oxide
• 10 mg lutein and 2 mg zeaxanthin

Advanced Wet AMD
The treatments described below offer symptomatic relief and are not a cure
VEGF Injections
VEGF is a protein that promotes formation of abnormal new blood vessels. Anti-VEGF injection therapy prevents this growth and patients may need multiple monthly injections.

Photodynamic therapy
This involves cold laser treatment in specific areas of the retina. This procedure is used less commonly than anti-VEGF injections, and is usually given in combination with anti-VEGF therapy for specific types of neovascular AMD

Laser Surgery
Not a common treatment. Uses intense hot laser in specific cases. May damage healthy tissue but prevents severe visual loss that would occur later

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