Reduced fluence rate PDT

Abstract

The invention relates to the use of reduced fluence rate PDT to treat neovasculature, particularly choroidal neovasculature (CNV). Reduced fluence rate PDT decreases the likelihood of molecular oxygen being the limiting factor in the photodynamic reaction so that the concentration of either photons (light intensity) or photosensitizer in the target tissue controls the photodynamic reaction.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application is a continuation of U.S. patent application Ser. No. 10 / 072,009, filed Feb. 6, 2002, which claims benefit of priority from U.S. Provisional Patent Application No. 60 / 266,960 filed Feb. 6, 2001. The entire contents of both are hereby incorporated by reference in their entirety.TECHNICAL FIELD [0002] The invention relates to the use of reduced fluence rate photodynamic therapy (PDT) in the treatment of unwanted or undesirable neovasculature, especially that of the choroid. The invention is particularly advantageous in the treatment of ocular conditions and diseases. BACKGROUND ART [0003] Neovascularization occurs when either there is proliferation of blood vessels in tissues that would otherwise not contain or there is a growth of a different kind of blood vessel in a tissue. Unwanted neovascularization is associated with a number of disease conditions, such as that seen to occur with tumor growth or vision loss. One exa...

AI Technical Summary

Benefits of technology

[0011] The present invention provides PDT with a lower amount of light per unit time (a lower fluence rate) to treat neovasculature and CNV. With reduced fluence rates, molecular oxygen concentrations around PS molecules in the CNV are less likely to become the rate-limiting factor in the photodynamic production of oxygen singlet free radicals. With a reduced fluence rate, the concentration of either photons (light intensity) or PS, rather than molecular oxygen, in the tissue would control the photodynamic reaction, resulting in better selectivity to the CNV, less damage to the normal choriocapillaris and possibly to the retinal pigment epithelium (RPE), and reduction of post-treatment hypoxia and resultant production of angiogenic factors. These effects would lead to improved visual outcome and a prolonged time period without leakage.

[0012] By minimizing the damage to the choriocapillaris and the response to that injury using a reduced fluence rate, the invention provides improve visual outcomes as well as lower rates of recurrence and CNV progression. Use of the invention is also expected to reduce the need for retreatments.

Problems solved by technology

In the presence of excess radiation during PDT, either molecular oxygen or PS may be rate-limiting in the production of free radicals.

Under conditions where a PS is present at high concentrations, molecular oxygen is potentially the rate-limiting molecule.

Where molecular oxygen is a limiting factor, irradiation beyond that necessary to activate the photosensitizer (PS) and generate singlet oxygen during PDT (or “excess irradiation”) may be inefficient because the continued activation of PS is unable to generate any additional singlet oxygen.

Moreover, the excess irradiation is likely to be counterproductive in the treatment of CNV by undermining the preferential accumulation of PS in the CNV.

This continued activation of PS is likely aggravated by the higher oxygen tension found in normal choriocapillaris than in CNV and results in unwanted and / or undesirable damage to the surrounding normal tissue.

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