Significance: The interocular difference in the ganglion cell-inner plexiform layer thickness showed a significant correlation with the diabetic retinopathy (DR) severity.

Purpose: The purpose of this study was to analyze the interocular differences in the foveal, retinal nerve fiber layer (RNFL), and ganglion cell-inner plexiform layer (GC-IPL) thickness of DR patients using spectral-domain optical coherence tomography.

Methods: A total of 508 eyes from 254 patients with different severities of DR and 184 eyes from 92 control subjects were included. The GC-IPL, foveal, and RNFL thicknesses were measured, and the interocular differences in these thicknesses were correlated in control subjects and DR patients.

Results: The interocular difference in the average GC-IPL thickness significantly increased with the severity of DR. The interocular differences in the average GC-IPL thicknesses of the severe nonproliferative DR (NPDR) and the proliferative DR patients were significantly higher than those of the control group. However, there was no significant difference in thickness between the control group and the group with mild to moderate NPDR. In the group with proliferative DR, the interocular difference in the average GC-IPL was greater than those in the central foveal and RNFL thicknesses. Multivariate regression analyses showed that the DR severity and the interocular difference in central foveal thickness were significantly correlated with the interocular difference in the average GC-IPL thickness.

Conclusions: The interocular differences in the central foveal, RNFL, and GC-IPL thicknesses significantly increased with increased DR severity. However, there was no significant difference between the control group and the group with mild to moderate NPDR. The GC-IPL differences showed a significant correlation with DR severity. These findings may be an indicator of DR progression.