Sonographic Measurement of the Optic Nerve Sheath Diameter (ONSD) and Eyeball Transversal Diameter (ETD) in Benin Healthy African Adults

Abstract

Background: Measuring optic nerve sheath diameter (ONSD), a relatively recent technique, allows an indirect and non-invasive diagnosis of intracranial hypertension. The ONSD ratio to eyeball transverse diameter (ETD) increases this reliability of the technique. The objective of this study was to determine the normal ONSD and its ratio with ETD in black African adults in Benin. Methods: A descriptive cross-sectional study was conducted between May 2019 and August 2019. Ultrasound ONSD and ONSD/ETD ratio were measured in 210 healthy adults received in the medical imaging department of the Borgou and Alibori University Hospital Center in Benin. The ONSD corresponded to the average of 12 measurements (03 horizontal and 03 vertical for each eye) taken 3 mm behind the papilla. The transverse ETD corresponded to the average of 03 measurements. Results: The mean ONSD was 4.20 ± 0.28 mm (95% CI = [4.17; 4.24] mm and 95th percentile = 4.70 mm). The mean ETD was 24.25 ± 1.10 mm. The ONSD/ETD ratio was 0.17 ± 0.01 (95% CI = [0.17; 0.17] and 95th percentile = 0.19). There was no difference between vertical and horizontal ONSD and between right and left ONSD. The ONSD and the ONSD/ETD ratio were not correlated with any of the socio-demographic and anthropometric characteristics studied (sex, age, ethnicity, weight, height, body mass index, head circumference and waist circumference). The ONSD was associated with ETD (p < 0.001 and r = 0.55). Conclusion: An ONSD and an ONSD/ETD ratio respectively greater than 4.70 mm and 0.19 should suspect intracranial hypertension. The ONSD/ETD ratio may be a better indicator of HICT because of its small variation.