DISPARITY BETWEEN FUNDUS CAMERA AND SCANNING LASER OPHTHALMOSCOPE INDOCYANINE GREEN IMAGING OF RETINAL-PIGMENT EPITHELIUM DETACHMENTS

Purpose: Indocyanine green (ICG) angiograms of each of five patients w ith retinal pigment epithelium (RPE) detachments were made using first a Topcon fundus camera and then a Heidelberg scanning laser ophthalmo scope (SLO); for each patient, both types of angiograms were obtained on the same day. In each case, the serous fluid appeared bright throug hout the fundus camera studies and dark throughout the SLO studies. Th is study sought to explain the disparity in the appearance of the lesi ons in the two kinds of images and to determine whether there was dye in the serous fluid. Methods: Simple model eyes were constructed to de monstrate the effects of Mie light scatter and integrating sphere beha vior of the sclera on ICG image formation by the fundus camera and SLO optics. Analysis was made of both the clinical angiograms and model e ye images to structure an explanation for the disparate RPE detachment angiographic images. Results: Indocyanine green fluorescent light fro m choroidal vessels adjacent to the lesions and scattered by the turbi d serous fluid accounted for the lesion brightness seen in the fundus camera images. The models confirmed that SLOs suppress scattered light . Conclusions: The apparent fluorescence of serous fluid beneath RPE d etachments in fundus camera early-phase ICG angiogram images is not at tributable to the presence of dye; rather, it appears to be attributab le to serous fluid light scatter of fluorescent light arising from adj acent fluorescent structures. This light scatter is a consequence of t he fundus camera illumination and recording optics and is not present in SLO-generated images. The necessity of understanding such phenomena as absorption, diffraction, polarization, and scatter of light and ro utinely applying them to ICG angiogram interpretation is underscored w hen it is shown that they offer simple explanations for unusual or une xpected angiographic results, as in the case of the patients with RPE detachment discussed here.