A computer-based method to quantify the classic pattern of choroidal neovascularization in order to monitor photodynamic therapy.

Background: Photodynamic therapy (PDT) is a new treatment modality which relies on a nonthermal light exposure of choroidal neovascularization (CNV) which has accumulated a photosensitizer, to produce a photochemical thrombosis. The aim of the present study was to develop a more quantitative outcome parameter that can be used to optimize a number of treatment parameters which in PDT are larger than many other modalities.

Methods: Nine patients underwent up to four standardized fluorescein angiography (FA) examinations on a Zeiss 30 degrees retinograph using Kodak Trimax film. The 35-mm pictures were digitized. The CNV size was evaluated using the NIH Image 1.60 software, comparing the CNV surface to the disk area. The fluorescence intensity was measured comparing the grayscale fluorescence levels of the CNV classic pattern with the mean grayscale level of control areas. A combination of the CNV size parameter with the fluorescence contrast parameter was called "integrated contrast" (IC). The IC amplitude was then used to describe and compare the fluorescence before and after PDT.

Results: FAs on three normal patients defined the normal range of the IC. IC measurements on two patients with a classic CNV who underwent FA examinations respectively 1 and 3 months apart demonstrated the robustness and the reproducibility of the method. IC measurements on three patients who underwent PDT with three different treatment parameters demonstrated the feasibility of using this IC measurement as a PDT outcome criteria.

Conclusion: We have developed a method to transform a qualitative clinical evaluation of CNV leakage into a more quantitative grading.