Age-related Macular Degeneration

Background

  • Commonest cause of blindness in the Western world in patients over 65.
  • Two types

Dry ARMD (85%)

Background

  • Dry (non-exudative) ARMD accounts for the majority of patients with ARMD.
  • srongly related to age- rare to have a case in someone <50
  • the most common cause of blindness in those >50 in the western world
  • A family history will greatly increase the risk as some genes seem to be inherited in an autosomal dominant fashion.
    • CFH gene (Ch1)
    • BF (complement factor B) gene and C2 (complement component 2) gene (Ch6)
    • LOC gene (ch10)
  • Smoking and obesity are also independent risk factors.

Pathophysiology

  • Degeneration of the retina and choroid  in the posterior pole (macular region) due to either atrophy (common) or retinal pigmented epithelium (RPE) detachment
  • This degeneration is preceded and accompanied by yellow extracellular deposits just under the RPE (known as drusen)
    • made of proteins (inflammatory/immune/plasma) and lipids- and are hyalinated (this is seen at ophthalmoscopy)

Presentation

  • Deteriorating central vision (since this is a macular problem).
    • In dry ARMD, there is a gradual loss of central vision (scotoma).
    • This may begin as a distortion (metamorphopsia) e.g. curving of straigt lines.
  • Examination
    • The first sign is the appearance of drusen on fundoscopy in the macular area of both eyes.
    • Atrophy of the macular appears later as a pale, mottled region (the reason for the mottled appearance is because of atrophy and secondary RPE hyperplasia).
    • You may also be able to see underlying vessels if the atrophy is severe enough.

Investigation

  • Fluorescein angiography and OCT may be used to identify choroidal neovascularisation in the macular area.
    • This will confirm the diagnosis but clinical suspicion is often enough.

Management

  • no known cure for dry ARMD.  The use of magnifying aids may help initially but will not improve symptoms (quality of life measure)

Wet ARMD (10-15%)

Background

  • Wet (exudative) ARMD, although not accounting for the majority of ARMD cases, accounts for the majority (90%) of severe visual loss and there is a high chance of second eye involvement.
  • It is also a much faster progressing disease.
  • Around 10-20% of people with dry ARMD will progress to the wet type.
  • Wet ARMD is also a disease of age, and is possibly more common in women than in men.
  • Family history and genes (see above) is a risk factor and hypertension (PMHx) may play a role too.

Pathophysiology

  • The mechanism to wet ARMD has similar features of the dry type but the damage to Bruch’s membrane caused by the drusen (Bruch’s membrane is the innermost layer of choroid) causes a release of vascular endothelial growth factor (VEGF) that causes neovascularisation of the choroid.
    • The vessels are not well formed so release an exudate that further damages the retina and can cause scarring at end-stage disease.

Presentation

  • Patients with wet ARMD generally have a much faster progression than those with dry type, but symptoms are generally the same (possibly with more severe distortion symptoms initially; also tends to present in one eye due to the acute nature of this type).

  • Examination
    • In contrast to dry ARMD, as well as atrophy and drusen, there are also choroidal neovascularisation, seen as small, focal, pale pink-yellow or green-grey elevations at the macula.
    • Microhaemorrhage or other exudates may be seen from leaky abnormal new vessels.

Investigation

  • Fluorescein angiography is of more use in the wet form than the dry form as any neovascularisation can be better visualised.  Depending on how much of the new vessels are seen, neovascularisation can be described as classic (clearly delineated) or occult (full extent not visible).

Management

  • In contrast with the dry type, there are several approaches that can be made with wet type:
    • Anti-VEGF (macugen/lucentis/avastin)- injection of anti-vegf works by inhibiting the VEGF and thus preventing neovascularisation.
  • Photodynamic therapy- works by ablating the newly formed vessels and preventing further growth (rarely done now)
Advertisements

2 thoughts on “Age-related Macular Degeneration”

  1. I like your summary of ARMD. I found your link by searching on LOC gene. You reference it in another chapter, but there is a dead end. 😦

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s