Age-related macular degeneration (ARMD)
 

A dry ARMD showing drusen with areas of RPE atrophy. Soft drusen Elevated macula with exudate due to  choroidal neovascularization and  pigment epithelium detachment.

Age-related macular degeneration is another popular macular case. You will be expected to know the Macular  Photocoagulation Study and TAP study on photodynamic therapy (which is currently in vogue). The macula contains drusen. In the non-exudative type there are areas of RPE atrophy. Confluent areas of atrophy  form geographic atrophy (see picture above). In the exudative (wet) type there may be hard exudates with or without subretinal haemorrhage.  The  macula may be  elevated due to RPE atrophy.  In chronic exudative type, the macula contains fibrosis with RPE atrophy. Other features to look for: examine the opposite eye for similar changes. Age-related macular degeneration is always bilateral. (In younger  patients, consider Doyne's disease or familial inherited drusen or Stargardt's disease).

Questions:

1. What does the Macular Photocoagulation Study show with regard to age-related macular degeneration?

Answer
Macular Photocoagulation Study shows that laser is useful in treating extra-foveal neovascularization.

2. How useful is laser treatment in treating subretinal neovascularization caused by ARMD?

Answer
Although Macular Photocoagulation Study shows the usefulness of laser in extra-foveal subretinal neovascularization. The great majority of patients in clinical practise are not suitable for laser due to the presence of subfoveal choroidal neovascularization. Even in treated case, about 50% shows recurrence within the first three years.

3. What is the difference between classical and occult choroidal neovascularization?

Answer
Classical choroidal neovascularization is well-defined and on fluorescein angiography shows localized area of hyperfluorescence which increases with time.
Occult choroidal neovascularization is poorly defined and on fluorescence angiography there are areas of diffuse hyperfluorescence.

4. A 63 year-old GP with a past history of wet ARMD was reviewed in your clinic. He had with him a recent paper cutting on photodynamic therapy performed by some hospital in the North. How would explain to him the theory behind this therapy?

Answer
Photodynamic therapy or PDT is a new treatment for exudative ARMD. It is a relatively selective form of treatment for choroidal neovascularization. It is a two-step process that involves the infusion of the photosensitizing dye followed by the application of the appropriate wavelength light to the target tissue. The dye is administered intravenously. A short waiting period between the dye infusion and the light application is needed to allow for clearance of the dye out of the surrounding normal retinal choroidal vasculature while it localizes in the target tissue ie the choroidal neovascularization. A predetermined amount of laser is delivered to the choroidal neovascularization over 60 to 90 seconds. The laser is specific for the absorption peak of the particular dye used. The most commonly used dye in the study so far is verteporfin a benzoporphyrin derivative.
PDT works by causing direct endothelial cell damage and unlike conventional laser there is no damage to the surrounding tissue.
The benefit of photodynamic therapy has been shown by the TAP study (The treatment of age related macular degeneration by photodynamic therapy)
 

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Classic choroidal neovascularization. Refer to the fluorescein angiography below for the complete  fluorescein angiography.

Occult choroidal neovascularization Return to the top

 
 

A patient with a right classic subretinal neovascular membrane.