The photodynamic therapy is an extremely innovative and promising method that a few years ago had an important development for the treatment of sub-retinal neo-vascularizations, complications which most of times are associated with the Senile Macular Degeneration (SMD).

In fact we remember that some time ago the most utilized therapy for these pathological processes was the laser photo-coagulation, but it had a rather limited effectiveness because of the high number of relapses noticed; besides that the percentage of sub-retinal neo-vascularizations considered untreatable because of their excessively central position was still very high, ranging around values of 60-70%, even if the verteporphirina angiography has increased the chances for a laser therapy. Other optional therapies such as surgical excision, or macular transfer are rarely actuated and only for selected particular cases, because of possible serious collateral effects. Neither radiotherapy nor the uses of interferon have produced any positive result for the treatment of macular pathologies.
After these facts, the PHOTODYNAMIC THERAPY (PDT) can be considered since now a good optional method to the laser therapy.
The drug adopted (VERTEPORPHIRINA) has been tested for the treatment of the skin cancers and proved to be capable of inhibiting the vascular supply to the new tissue through a toxic action on the vascular shaft inner part; this action induces the vessel obstruction by means of a real "plug" that prevents the nutrition of the cancer cell which finally decays. The purpose of therapy in the ophtalmological field is the selective obstruction of the choroidal neo-vessels with little or no damage for the neighboring tissues, which is the contrary of the traditional laser behavior.
The treatment is made through two steps; during the first one the drug is injected intravenously and it lays inside the "ill" vessels; during the second step, the drug action is stimulated by a low rate laser for about 80 seconds thus producing the selective destruction of the neo-vascularizations. The drug is completely excreted within 24 hours and during this time it is recommendable not to expose to the sunlight, as the substance is photosensitive.
Unfortunately, during the 2-3 months following the treatment, the occurrence of relapses is regular so that a new operation is needed.

How is PDT acting?

The drug injected inside the vein operates a selective connection with the neo-vascular membrane endothelium. The coloring substance, excited by the laser light, produces oxygen radicals with cells granulation and following obstruction of vessels. In this way the overlaying and adjoining retinal capillaries and the underlying vascular shaft should not be involved.
Recently a new hypothesis about the drug action has been suggested: the radicals produced by the therapy destroy the red corpuscles located on the membrane and the hemoglobin released acts as a vasoconstrictor on the endothelium cells of the neo-vascular membrane. The surrounding vessels would also be damaged, but since they have wider sizes and are more hemodynamical, damages would not be devastating.

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Results

After one year, the first clinical results have been issued. 61% of the patients treated by verteporphirina, against 46% of the patients treated by a placebo, had maintained a constant or even better visual capability.
The collateral effects were very small and included some temporary visual trouble (18%), some skin alteration on the injection point (13%) and photosensitivity (3%).

Up to February 2000 the drug registration was approved in Switzerland and it is therefore available even if its cost is high.
We therefore hope that photodynamic therapy can be a good treatment for the macular degeneration related to aging or to some kind of myopic macular pathology or generally to all kinds of neo-vascularizations of the rear pole (diabetic retinal pathology?).
Certainly the availability of a therapeutic option will lead to the development of new drugs thus producing also the reduction of PDT costs.

SUMMARY The percentage of sub-retinal neo-vascularizations which cannot be treated by laser photo-coagulation is very high: 60-70% The therapeutic surgical options are often disappointing or hardly applicable; the pharmacological therapies are still under testing. The PHOTODYNAMIC THERAPY on the contrary represents a good optional choice to the laser photo-coagulation and it is immediately available The treatment is performed through a drug that excites a selective thrombosis inside the choroidal neo-vessels with little damage for the neighboring structures.