Influence of disc area on retinal nerve fiber layer thickness measurement by spectral domain optical coherence tomography

To examine the effect of optic disc area on peripapillary RNFLT (retinal nerve fiber layer thickness) measurement at circle diameter of 3.4 mm around optic nerve head using spectral OCT/SLO (Optical coherence tomography/scanning laser ophthalmoscope). In this prospective, cross sectional study, one hundred and two eyes of 102 normal subjects underwent RNFLT and disc area measurement using spectral OCT/SLO. Based on disc area, subjects were divided into three groups i.e., 4 mm2 (34 eyes). The effect of disc area on RNFLT parameters was analyzed using linear regression analysis. The mean and quadrant RNFLT did not show significant correlation with disc area in subjects with disc area of 4 mm2, average RNFLT, superior and temporal quadrant RNFLT showed negative correlation with disc area, which was statistically significant (P = 0.004, P = 0.005 and P = 0.002, respectively). In healthy eyes of disc area 4 mm2. Hence, RNFLT measurement by OCT in eyes with optic disc area of >4 mm2 should be interpreted carefully.