macular degeneration
Wet AMD: PDT
Photodynamic Therapy (PDT)
This therapy aims to destroy the membrane without causing damage to the surrounding normal retinal tissue. It does this by utilising the light-sensitive nature of a chemical dye, called Visudyne®, to allow the use of a non-destructive low powered "cold" laser beam.
The dye is injected into the blood stream over 10 minutes. The dye has a particular affinity to certain receptors that are more concentrated in abnormal blood vessels than in normal (retinal) blood vessels. In this way the dye is targeting itself to the membrane. Fifteen minutes after the start of the dye injection, a cold laser beam is used to activate the dye. This process leads to chemical reactions inside the membrane blood vessels causing them to become damaged and ultimately to "close up" by coagulation. In theory this should be a perfect treatment however in practice what we normally see is early success in nearly all cases with membrane closure but very often the blood vessels recover and around three months later recurrence of the membrane is usually the norm. The treatment is therefore repeated up-to 3 times in the first year and 1 or 2 times in the second year of follow up and may even be required once or twice in the third year.
The drug used in PDT causes sensitivity to light and patients are advised to stay indoors and away from direct sunlight for 48 hours after treatment. Other side effects include decreased vision that is usually temporary lasting up to 14 days.
There is also a small risk of irreversible severe vision decline after PDT; the risk of this is quoted as between 1%-4%.
PDT is not a cure for wet AMD. It should be thought of as a therapy that attempts stabilise the condition and the vision. Unfortunately even with PDT, people with wet AMD can still lose some vision however this loss is likely to be considerably less than what would happen without PDT.
For patients with either pure classic or mainly classic membranes in wet AMD, PDT is able to reduce the chance of significant vision decline occurring over a two year period by around 50%.
For patients with pure occult membranes the chances of experiencing significant vision decline over a two-year period can be reduced by around 30% with PDT.
Results
