Quantification of Optic Nerve and Sheath Diameter by Transorbital Sonography: A Systematic Review and Metanalysis

Background and purpose To date, normal values for optic nerve diameter (OND) and optic nerve sheath diameter (ONSD) for transorbital sonography (TOS) have only been reported by individual small-scale studies, exposing a great variability in the measurement of the OND and ONSD. Methods We performed a systematic review and metanalysis of available to date studies on TOS evaluation of adults without elevated intracranial pressure to provide an overview of the published literature, measuring methods and further specify normal values for OND and ONSD. Results In total, we included 39 studies with 2,927 healthy volunteers (mean age 36.1 years, 44.4% female), so that a total of 5,854 eyes were examined. All pooled analyses were based on random effect models. Mean values for OND were provided in 13 studies. Calculated mean pooled OND value was 3.08 mm (95% confidence interval [CI], 2.9-3.25), with low heterogeneity across studies (I2 = 12.7%). Thirty-four studies provided mean values for ONSD measurement. The pool of mean ONSD measurements was 4.78 mm (95% CI, 4.63-4.94), with evidence of substantial heterogeneity between estimates ONSD (I2 = 50.6%). There were no significant differences (P = .139) in the subsequent subgroup analysis for the different geographic continents. Also, no significant differences could be recorded for the effect of age (P = .824) or gender (P = .093). Conclusions TOS is a frequently described and widely used method. We provide reference values of OND and ONSD that are based on metanalytical analysis. Different measuring methods of ONSD result in higher heterogeneity. Subgroup analysis revealed no significant correlation between ONSD and age, gender, or geographic origin.