Definition

Age-related macular degeneration (AMD) is the term applied to changes, without any other obvious precipitating cause, which occur in the central area of the retina (macula) in people aged 55 years and over.

Subtypes

• Early AMD — a combination of multiple small drusen, few intermediate sized drusen (63–124 micrometres in diameter), or mild abnormalities of the RPE.

• Intermediate AMD — characterized by any of: numerous intermediate sized drusen; at least one large druse greater or equal to 125 micrometress in diameter; geographic atrophy not involving the centre of the fovea.

• Advanced AMD — characterized by one or both of geographic atrophy of the RPE involving the foveal centre ('dry AMD'), or neovascular AMD ('wet AMD').

Pathology

• Drusen — collections of lipid and protein material which occur beneath the retinal pigment epithelium (RPE) and within Bruch’s membrane.

• Abnormalities of the RPE — areas of hypopigmentation or hyperpigmentation.

• Geographic atrophy — one or more sharply demarcated areas of depigmentation (atrophy) of the RPE which can enlarge over time.

• Neovascular (exudative) AMD — the development of new blood vessels beneath and within the retina.
  The new vessels are unlike normal vessels and easily bleed or leak blood constituents, resulting in distortion and scarring of the retina.

Prevalence

Advanced AMD is the commonest cause of severe visual impairment in older adults in the developed world and is responsible for two-thirds of registrations of visual impairment or blindness in the UK.

In the UK, advanced AMD affects about 2.4% people over 50 years of age.
The prevalence rises steeply with age affecting about 4.8% of those aged 65 years or older, and about 12.2% of those aged 80 years or older

Aetiology

The cause of AMD is unknown but established risk factors include smoking, a family history of AMD, and genetic factors.

Complications

• Visual impairment and blindness.

• Depression.

• Falls and fractures.

• Reduced quality of life.

• Generally, early and intermediate AMD are not associated with disturbances of central visual function but advanced AMD can cause severe visual impairment.

• Geographic atrophy tends to progress slowly.

• Untreated neovascular AMD can progress within weeks or months to cause severe visual loss.

Symptoms and Signs

• Painless deterioration or blurring of central vision, typically in a person aged 55 or more.

• Metamorphopsia: Distortion of vision, where straight lines appear crooked or wavy.

• Scotoma: A black or grey patch affecting the central field of vision.

• Difficulty reading, driving, or seeing fine detail (such as facial features).

• Flickering or flashing lights (photopsias).

• Difficulty adjusting from bright to dim lighting.

• Visual hallucinations (associated with severe visual loss).

On examination:

Visual acuity may be reduced, but may be normal.

With fundoscopy:

• Drusen.

• Pigmentary, exudative, haemorrhagic, or atrophic changes affecting the macula.

Treatment and prognosis

Management in secondary care includes intraocular injections of anti-angiogenic drugs for neovascular AMD.

Since anti-angiogenic drugs became available, the prevalence of blindness and visual impairment due to neovascular AMD has been considerably reduced.

Urgent referral to ophthalmologist within a week

If AMD is suspected, urgent referral to an ophthalmologist should be arranged within a week as treatment for neovascular AMD should be started promptly to preserve sight.