PHOTODYANAMIC THERAPY

Abstract

PDT is evolving rapidly as treatment modality for ocular neovascularization and tumors. PDT is an exciting and promising new treatment option for patients with CNV in whon1 a safe and selective treatment may be critical to prevent blindness. For many years thern1allaser photocoagulation has been the only accepted treatment, but nwnerous studies have shown that photocoagulation of subretinal vessels destroys the overlying retina as well as high recurrence rate. Thus, the ideal treatment of subretinal neovascularization should combines selective destruction of the subretinal vessels with minimal damage to their overlying retina. That is being achieved by photodynamic therapy. The tpain advantages of photodynamic_ therapy are its photosensitizing potency, absorption peak around 690nm enabling better penetration, rapid and selective accumulation by endothelial cells m neovasculature, and rapid clearance from the body.

Photodynamic therapy combines application of low intensity, non-thermal light with a photosensitizing agent to produce effects m tissue. Ex perimental studies suggest that main mechani sms of action are intravascular damage leading to thrombus formation and selective vascular occlusion, and direct endothelial damage results from the production of singlet oxygen and other free radicals with alten1ation of cell membranes.

The most important advantage of this therapy is the potential selective destruction of the choroidal neovascularization tissue retinal and choroidal tissue ' surrounding the choroidal neovascularization may be minimally disturbed, thus maintaining function of surrounding sensory retina, retinal pigment epithelium and choroid.

With the development of second generation photosensitizer there is much increase in efficacy, better tissue penetration and marked diminished cutaneous photosensitivity.

Few ocular or systemic adverse effects are associated with photodynamic therapy. The photosensitivity reactions are the most common systemic complication; this can be avoided following the post treatment instructions. The ocular· adverse effects are minimal in the form of subretinal hemorrhage, increased fibrosis associated with CNV and increased RPE atrophy.

The improved efficacy of PDT demonstrated in recent experimental and cliillcal studies suggests that PDT show a promise as a primary treattnent for ocular neovascularization and tumors.