AMD membrane and basal lamina of the RPE.

AMD – Age-related Macular Degeneration

RPE – retinal pigment epithelium

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Age-related Macular Degeneration – also
referred to as AMD – can be divided into dry AMD and wet AMD. Macular
degeneration is defined as the loss of macular function from the degenerative
changes of ageing and so mainly affects the central vision.  

80-90% of all AMD cases are of the dry form1
and 10-15% are wet, however 80% of severe vision loss relating to AMD is due to
the wet form2.

Due to wet AMD having such a severe impact
on vision it is important to prevent dry AMD developing into the wet form and
so prevention of this is key.

 

Pathogenesis

 

Dry AMD develops slowly and in stages. The
first initial pathological change is basal laminar and basal linear deposits
between the plasma membrane and basal lamina of the RPE. These start of very
small and can often be undetectable with an ophthalmoscope4.

These deposits then develop and increase to
form drusen between the retinal pigment epithelium and Bruch’s membrane.

These deposits and drusen that form are due
to oxidative stress throughout the patient’s life through UV light exposure and
ageing that causes the accumulation of Advanced Glycation end-products and
photo-oxidation end products, with inflammation and hypoxia playing a major
role3. Along with this hyper/hypo pigmentation of the RPE results
and also thickening of Bruch’s membrane occurs with age3.

The blood vessels in the choroid show a
narrowing of the lumens and decrease in the vessel density. Atrophy of the RPE
can also occur showing the absence and death of RPE cells leading to the loss
of photoreceptors. This can cause vision loss whilst the AMD is still in the
dry phase4.

 

1 – (Mitchell J, Bradley C.

http://www.hqlo.com/content/pdf/1477-7525-4-97.pdf )

2 – (Jager RD et al. N Engl J Med 2008; 358(24):
2606–2617)

3 – (Ocular Disease University of
Manchester Macular lecture)

4 – (Age-Related Macular Degeneration:
Etiology, Pathogenesis, and Therapeutic Strategies Jayakrishna Ambati, MD,1,2
Balamurali K. Ambati, MD,2,3 Sonia H. Yoo, MD,2,4 Sean Ianchulev, MD,2 and
Anthony P. Adamis, MD2,5,6 – SURVEY OF OPHTHALMOLOGY VOLUME 48 • NUMBER 3 •
MAY–JUNE 2003)

 

Risk
Factors

 

There are many risk factors, which can lead
to the formation of dry AMD. The main one is being elderly as AMD increases
with age. Having a family history of the condition increases the chances that
other family members will also get it with the gene variant Y402H being linked
to drusen formation.

Smoking increases the risk by two times and
also having other conditions such as cardiovascular disease and hypertension is
also a risk factors. Having a diet that lacks fruits and vegetables and consisting
of high amounts of unsaturated fats can increase the risk. Dry AMD is more
likely in those with light hair, light skin and light eyes and also in individuals
who have had more UV light exposure and is also known to pose more risk for
females. 2

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