Evaluation of photodynamic therapy in clinical studies
Photodynamic therapy (PDT) primarily allows a selective occlusion of choroidal neovascularization (CNV) without associated alteration of adjacent sensory retina and accompanying visual loss. Repeated application induces a progressive reduction of leakage from the neovascular complex over time and provides long-term visual stabilization. However, the method appears to require further evaluation regarding parameters, long-term results and indications.
Patients and methods: Clinical studies phase I/II and phase III exclusively include patients demonstrating subfoveal CNV angiographically. Three different light-activable compounds are under investigation: Benzoporphyrin (Visudyne), tin ethyl etiopurpurin (Purlitin) and lutetium texaphyrin (Lutex). All of these sensitizers are administered by i.v. injection and are activated intraocularly by light provided by specifically designed diode lasers emitting in the red wavelength range (690, 664 or 732 nm).
Results: A prospective, randomized, double-masked study evaluating Visudyne-PDT in CNV with classic component in AMD (TAP-Investigation) was just terminated, two-year data are being analyzed. A prospective, randomized trial with Visudyne-therapy in early classic CNV in AMD, isolated occult CNV in AMD and CNV secondary to pathologic myopia (VIP trial) will provide first results after termination of the first study year in mid 2000. Pilot studies in CNV associated with ocular histoplasmosis syndrome (OHS) demonstrate positive results. An own, independent study seeks to improve selectivity and long-term efficacy by optimization of the dosimetry. The Purlytin-study using PDT in CNV with any classic component resulted in a mean increase in visual acuity of 2.7 lines after 3 months and is now collecting participants for a prospective, randomized AMD only trial. An open-label pilot study in Europe has provided evidence for the efficacy of Lutex therapy in subfoveal CNV, randomized trials are being designed. Lutex may also be used as a fluorophore for diagnostic angiography.
Conclusion: Three sensitizers are currently under evaluation in five clinical trials. One compound, benzoporphyrin, is legally admitted for clinical use in predominantly classic CNV in AMD. New trial concepts are evaluating an optimization of treatment parameters, a reduction of treatment repetitions and expanded indications for benzoporphyrin therapy.
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