Diabetic retinopathy: I. The measurement of intercapillary area in normal retinal angiograms

A method for the quantitation of areas of non-perfusion of retinal angiograms is described. The values for the area of the foveal avascular zone (FAZ) and the intercapillary areas in the perifoveal region of ten angiograms of normal subjects were determined. The reproducibility of measurement between and within observers was good, correlation coefficients being 0.9963 and 0.9945, respectively, for the FAZ. The inter- and intra-observer coefficients of correlation for the perifoveal intercapillary areas were 0.9284 and 0.8687, respectively. The upper limit of normal intercapillary area was determined to be 0.07 mm2 in the first degree from the FAZ, 0.04 mm2 in the second degree and 0.025 mm2 elsewhere in the macular field.