Fundus reflectometry for photocoagulation dosimetry

A dosimetry technique has been developed which utilizes three-wavelength fundus reflectometry, a quantitative model of fundus reflectance, and a model of thermal tissue damage to control photocoagulation lesion size. The fundus reflectance model uses Lambert-Beer's law exponential attenuators to describe the ocular media, retinal pigment epithelium (RPE), and choriocapillaris transmission characteristics while the choroid is described as a Kubelka-Munklike homogeneous scatterer/absorber. Three reflecting layers are included in the model at the retinal inner limiting membrane, Bruch's membrane, and the sclera. Measured lesion size variability contained components which resulted from variations in choroidal blood and melanin and RPE melanin concentration. Photocoagulation dosimetry was found to reduce the photocoagulation lesion size coefficient of variation for red light from 45% to 10% for the control and dosimetry cases, respectively. Similar improvement was noted for yellow photocoagulation light.