Peripapillary Retinal Nerve Fiber Layer ThicknessMeasurement by Three-Dimensional OpticalCoherence Tomography in a Normal Population

Purpose: To determine peripapillary retinal nerve fiber layer (RNFL) thickness valuesby three-dimensional optical coherence tomography (3D-OCT) in a normal Iranianpopulation and to evaluate the concordance of these measurements with those obtainedby the second generation of optical coherence tomography (OCT II).Methods: In a cross-sectional observational study, 96 normal Iranian subjects 20-53years old were enrolled. Peripapillary RNFL thickness in one randomly selected eye ofeach subject was measured by 3D-OCT and also by OCT II. Standard achromaticperimetry, 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.Results: Mean peripapillary RNFL thickness measured by 3D-OCT (75.50±8.38) ìm was significantly less than that measured by OCT II (144.10±33.32 ìm) (P 0.001). Using 3DOCT,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 cornealthickness (P=0.66) and disc area (P=0.31). However, a positive correlation was foundbetween peripapillary RNFL thickness and corneal diameter (P=0.03).Conclusion: 3D-OCT seems to yield lower RNFL thickness values as compared to OCTII. It seems advisable to obtain separate baseline measurements when using differentgenerations of OCT machines.