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macular degeneration

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Age related macular degeneration (AMD) is defined as age related changes which occur without an obvious cause in the central part of the retina (macula) in people over the age of 50 years (1). Senile macular degeneration is the most common cause of registrable blindness in the UK in patients over the age of 65.

The disease is characterized by the presence of drusens (lipids and protein deposits under the retina), often with associated retinal pigment epithelial abnormalities (2).

In AMD, there is degeneration of the central retina (macula) and changes are usually bilateral. A broad spectrum of clinical findings occur. Visual acuity is reduced. Visual fields are unaffected by macular degeneration.

  • normally there is progressive loss of central vision
  • people retain some peripheral vision, but the ability to see well enough to recognise faces, drive and read is affected, and vision can deteriorate rapidly

There are two major clinical presentation of AMD (1):

  • geographic atrophy (GA, dry, non-neovascular)
    • is the presence of a discrete area of partial or complete retinal depigmentation with sharply demarcated, scalloped borders. Large choroidal vessels can be seen through the atrophic retinal pigment epithelium (1)
    • the visual loss progresses gradually (2)  
    • involvement of the central part of the macula is known as central geographic atrophy (2) and may result in central visual loss (3)
    • “dry AMD” is an earlier term used to describe various fundal signs (drusen and pigmentary changes, patchy areas of atrophy to geographic atrophy)
    • drusen and pigmentary changes are now termed as early AMD and the term dry AMD is reserved for GA (1).

  • exudative (wet, neovascular) AMD
    • characterised by choroidal neovascular lesions which develop when immature blood vessels from the choroid breeche the layer between the retina and choroid (Bruch membrane). These new blood vessel’s invade the subpigment epithelium and/or subretinal spaces, a process known as choroidal neovascularisation (CNV) (1,4)
      • these vessels leak easily which result in haemorrhage or detachment of the retinal pigment epithelium or the neurosensory retina
      • associated scar tissue formation will replace normal retinal tissue leading to visual impairment
      • it is responsible for around 90% of cases of severe vision loss (4)
      • if a patient has neovascular AMD in one eye, the risk of developing CNV in the second eye at 7 years is around 50% (3)
    • worst prognosis is carried by the exudative or wet form of senile AMD
      • if left untreated the complexes can expand rapidly resulting in severe loss of vision within 2 years (5)
    • are about 26,000 new cases of wet AMD in the UK each year and the condition affects more women than men
    • condition usually affects people who are over 50 years old and the risk increases significantly with age
    • most commonly cited risk factor for AMD is cigarette smoking; the risk of developing AMD is 3.6 times greater for current and former smokers than for people who have never smoked

Both these conditions can be seen in the same patient e.g. - dry AMD in one eye and wet AMD in the other or both dry and wet AMD in the same eye (8)

AMD is a painless condition that generally leads to the gradual impairment of vision, but it can sometimes cause a rapid reduction in vision

  • predominantly affects the central vision, which is used for reading and recognising faces
  • normal macular ageing changes are a common incidental finding on a routine visit to the optometrist, but AMD may also be detected this way before it is symptomatic, or people may present with difficulty in performing daily activities such as driving, reading and recognising faces

The consequences of this condition for vision can be severe

  • AMD is the most common cause of visual impairment in the developed world, and the Royal National Institute of Blind People (RNIB) reports that AMD is the most common cause of certification for vision impairment
    • in an Australian cohort study of people with early stage AMD, the risk of progression to intermediate or advanced AMD within 5 years was 17%
    • however, early AMD is not always significantly progressive because 83% did not progress and AMD lesions appeared to have improved and regressed in 8% of people.

The prevalence of late AMD in the UK among people aged 50 years or over is 2.4% (from a metaanalysis applied to UK 2007-09 population data)

  • increases to 4.8% in people aged 65 years or over, and 12.2% in people aged 80 years or over
  • same study found the prevalence of geographic atrophy to be 1.3 to 6.7%, and the prevalence of neovascular AMD to be 1.2 to 6.3%
  • estimates indicate that around 39,800 people develop neovascular AMD in the UK each year; given a total UK population of 60 million, this equates to 663 new cases per million per year.

There has been a significant increase in hospital activity in England for episodes with a primary diagnosis of AMD, from less than 10,000 episodes in the years 2005/06 to over 75,000 episodes in the years 2013/14

Notes:

  • a distinction can be drawn between 'early' and 'late' disease (9)
    • within 'late' disease, distinction should be drawn between disease that is
      • 'wet active' (neovascular lesions that may benefit from treatment),
      • 'wet inactive' (neovascular disease with irreversible structural damage) and
      • 'dry' (non-neovascular disease, including geographic atrophy)

    • an additional category - late AMD (indeterminate) - is introduced to reflect rarer subtypes

Reference:

Last edited 04/2018 and last reviewed 03/2021

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