Measurement of Peripapillary Retinal Nerve Fiber Layer Thickness by Three-Dimensional Optical Coherence Tomography in an Iranian Population

To determine peripapillary retinal nerve fiber layer (RNFL) thickness by three-dimensional optical coherence tomography (3D-OCT) in a normal Iranian population and to evaluate the concordance of these measurements with those obtained by the second generation of optical coherence tomography (OCT II). In a cross-sectional observational study, 96 normal Iranian subjects 20-53 years of age were enrolled. Peripapillary RNFL thickness in one randomly selected eye of each subject was measured by 3D-OCT and also by OCT II. Standard achromatic perimetry, corneal pachymetry and A-scan ultrasonographic biometry were also performed. Other study variables included age, gender, laterality (right versus left eye), refractive error, corneal diameter and disc area. Mean peripapillary RNFL thickness measured by 3D-OCT (75.50±8.38 µm) was significantly less than that measured by OCT II (144.10±33.32 µm) (P<0.001). Using 3D-OCT, no significant difference in peripapillary RNFL thickness was observed by gender (P=0.90) or laterality (P=0.17); RNFL thickness had no correlation with age (P=0.95), axial length (P=0.32), spherical equivalent refractive error (P=0.21), central corneal thickness (P=0.66) and disc area (P=0.31). However, a positive correlation was found between peripapillary RNFL thickness and corneal diameter (P=0.03). 3D-OCT seems to yield lower RNFL thickness values as compared to OCT II. It seems advisable to obtain separate baseline measurements when using different generations of OCT machines.