Correlation between the orbital and intraocular portions of the optic nerve in glaucomatous and ocular hypertensive eyes

Background/Purpose It has recently been reported that the retrobulbar optic nerve diameter (OND) and cross-sectional area (ONCSA) are reduced in glaucoma. This study was performed to investigate the correlation between the orbital and intraocular portions of the optic nerve. Methods One eye of 20 volunteers (16 glaucoma subjects, 4 ocular hypertension subjects) underwent optic disc analysis using Heidelberg retinal tomography, and echographic measurements of the retrobulbar optic nerve. Results The male-to-female ratio was 6.5:3.5, and the mean age of our sample (± SD) was 62.25 ± 13.7 years. Orbital optic nerve diameter and cross-sectional area correlated significantly and positively with the neuroretinal rim area (Spearman's rank correlation coefficient; OND: r s = 0.488, p = 0.0336; ONCSA: r s = 0.619, p = 0.0079), but not with any other topographical disc data. The retrobulbar optic nerve cross-sectional area-to-disc area ratio (ONCSA/D) was found to have a significant negative correlation with the cup area/disc area ratio (simple regression analysis; r = -3.948, p = 0.046), and a statistically demonstrable positive correlation with the neuroretinal rim area/disc area ratio (r = 0.451, p = 0.046). Conclusion The results of this study indicate that orbital optic nerve dimensions are a reflection of the neuroretinal rim area of the optic disc. Echographic measurements of the retrobulbar nerve may be additive to the traditional triad of raised intraocular pressure, field defects and glaucomatous optic neuropathy that suggests a diagnosis of glaucoma.