To compare the peripapillary retinal nerve fiber layer (RNFL) thickness in eyes affected by non-arteritic ischemic optic neuropathy (NAION) or glaucoma as determined by optical coherence tomography (OCT).

This cross-sectional institutional study included 18 eyes with NAION (at least 6 months since the acute event) and 29 eyes with glaucoma, both having localized visual field (VF) defects confined to one hemifield. Twenty-nine normal subjects served as controls. The fast RNFL thickness protocol (3.4) of the Stratus OCT (Carl Zeiss Meditec, Dublin, CA, USA) was used. The RNFL thickness and inferior maximum/temporal average (Imax/Tavg) and superior maximum/temporal average (Smax/Tavg) data corresponding to the hemifield with and without visual sensitivity loss were compared between NAION and glaucomatous eyes and with corresponding quadrants in normal eyes. The area under the receiver operating characteristic curve (AUC), sensitivities, and specificities were used to determine the OCT parameters that differ most in the two groups.

The mean RNFL thickness in the quadrants corresponding to the affected hemifield in the NAION and glaucomatous eyes was not significantly different (P > 0.9), but the values for both were decreased compared to the control eyes (P < 0.0001). The mean RNFL thickness in the quadrant corresponding to the unaffected hemifield was significantly lower in the glaucomatous eyes (73.8 ± 20.04 µ) than in the NAION eyes (96.6 ± 23.32 µ, P = 0.023), and in both study groups compared to the controls (117.2 ± 13.44 µ, P < 0.0001 for glaucomatous vs control eyes, and P < 0.025 for NAION vs control eyes). Smax/Tavg and Imax/Tavg of the quadrant corresponding to the unaffected hemifield had the strongest power to differentiate the two diseases (an AUC of 0.92).

Stratus OCT detected significant quantitative differences in RNFL thickness between glaucomatous and NAION eyes, both conditions with hemifield defects. These differences might hold a clue in understanding the processes involved in optic nerve injury.