Age-related macular degeneration

fundoscopy

ARMD is a leading cause of blindness, accounting for 40% to 50% of new cases of blindness. It causes severe loss of central vision.

Light-generated metabolic waste products accumulate in the retinal pigment epithelium (RPE), which results in degeneration and atrophy of the choroid capillaries. Drusen are invariably present and usually precede visual disturbances by many years.

There are two forms of ARMD. Atrophic ("dry") macular degeneration rarely results in a visual acuity worse than 20/80 (6/24). Exudative ("wet") or disciform macular degeneration is less frequent but potentially far more devastating.

In this type a fragile subretinal neovascular membrane develops that can distort the macula, which results in metamorphopsia and may lead to severe and sudden visual loss from retinal detachment.

Approximately 90% of people with ARMD have atrophic maculopathy; of those who are legally blind (visual acuity of less than 20/200 [6/60]) about 90% have exudative maculopathy

Funduscopy reveals drusen and fine pigment stippling in the macular area, which progresses to larger clumps of pigment. Although drusen are readily recognized by ophthalmologists and optometrists, sensitivity for their detection by primary care physicians is unknown.

Most fundi in people over 20 years of age will show drusen histologically; however, only one third of those examined clinically in people over 52 were found to have drusen.28 The presence of many drusen, pigmentary changes or "softening" should be detectable by primary care physicians.

Retinal photography is a standardized way to record abnormalities of the fundus, but it is not available to primary care physicians. Fluorescein angiography evaluates the vascularity of the fundus and determines capillary leakage, but it is unsuitable for screening.

Effectiveness of intervention

There was no effective treatment for ARMD before the introduction of laser photocoagulation. Bursts of argon (blue-green) laser energy are used to obliterate the neovascular changes.

In three randomized controlled trials photocoagulation was compared with no treatment among subjects over 50 years of age with drusen and subretinal neovascular complexes identified by means of fluorescein angiography.

In each study, photocoagulation improved preservation of visual acuity. Older patients and those with neovascular tissue distant from the fovea were the most likely to benefit.

The benefits of photocoagulation offer a rationale for early detection and observation of ARMD. Unfortunately, visual deterioration usually occurs and lesions progress beyond the point at which treatment is successful.

For example, in one study the condition was treatable in 80% of patients who presented to an ophthalmologist within 2 weeks after symptoms developed; this rate dropped to 40% among those who presented after 1 month and to less than 10% among those who waited 4 months.

Disciform ARMD may be amenable to treatment in up to 50% of patients if it is identified early enough. Treatment is most beneficial for patients with a visual acuity of 20/60 (6/18) or better. In the event of retinal detachment, there is no benefit to photocoagulation.

Photocoagulation using krypton red laser energy has been found to be no more effective than that using argon green laser energy.

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