Quantitative fluorescein angiography following diode laser retinal photocoagulation

Objective: An in vivo study was done to establish if laser-induced damage of the retina could be quantified using fluorescein angiography. Method This study was carried out on rabbit eyes (n = 6) with an 810 nm diode laser (spot diameter: 500 Ir-m, pulse duration: 1 second, power: 100 mW-400 mW) adapted on a slit lamp. Fluorescence measurements were performed with a fundus camera connected to a fluorescence imaging system. Fluorescence staining of the retina was evaluated by mathematical modeling. Lesions were correlated to laser parameters and to histologic data. Results: Image analysis shows that the laser lesions stained progressively. Fluorescence appears first at the borders of the lesion exhibiting a fluorescent ring. A progressive increase of the fluorescence into the central zone is observed. The maximum fluorescence intensity into the center of the laser spot is obtained after a delay depending on the laser energy. Below 100 a 20 mW, lesions are detectable by fluorescence imaging only. A fluorescence plateau appears for a threshold light dose above 200 +/- 20 mW. Mathematical modeling demonstrates that quantitative assessment of laser-induced damage to the retina is feasible using fluorescence imaging. Conclusion: The quantification of fluorescence staining in terms of both intensity and time can contribute to a better quantification of laser-induced damage. At last, since laser damage may mimic naturally occurring pathology, this method should also be considered to quantify different types of lesions. Lasers Surg. Med. 24:338-345, 1999. (C) 1999 Wiley-Liss, Inc.