Quantitative evaluation of retinal response to laser photocoagulation using dual-wavelength fundus autofluorescence imaging in a small animal model

Purpose. To demonstrate the usefulness of dual-wavelength fundus autofluorescence (FAF) imaging for noninvasive, quantitative monitoring of dynamic changes associated with healing of retinal photocoagulation lesions in a small animal model. Methods. Brown Norway rats, exhibiting substantial age-dependent lipofuscin autofluorescence, were used to characterize the kinetics of FAF recovery after retinal photocoagulation. An argon laser with a beam diameter of 100 μm, exposure duration of 0.1 seconds, and a range of laser powers (8-22 mW) were used to create subthreshold, threshold, and suprathreshold lesions. A modified retinal angiograph was used to obtain dual-wavelength FAF images at 488 and 514 nm to quantify and monitor changes in retinal fluorescence up to 6 months. Results. Compared to white light funduscopy, the FAF images exhibited heightened definition and clarity of lesion boundaries immediately after laser exposure. No significant reduction in FAF was measured at or below laser powers of 8 mW. Furthermore, a linear, dose-dependent decrease in FAF (R2 = 0.9605) was observed immediately after laser exposures of 13 to 22 mW. Complete recovery of baseline FAF was observed for 13.5 and 16 mW exposures at 3 weeks and 4 months, respectively. However, retinal damage was still evident at 6 months after suprathreshold exposure induced using 22 mW laser power. Conclusions. The accumulation of lipofuscin in the aged Brown Norway rat makes it a suitable small animal model for the characterization of laser-induced injury in the retina based on FAF. Dual-wavelength FAF measurements provide a sensitive, quantitative, noninvasive means of monitoring recovery of laser-induced retinal injury.