Fig. 3: Optic nerve sheath complex measurements.

a The 12 MHz transducer was placed over the upper eyelid of the test eye in a transversal plane. A sonographic slice provides the transversal view of the eye and the optic nerve sheath complex shows as a hypoechoic strip in the echogenic retrobulbar fat. b Schematic representation of the ultrasound optic nerve sheath complex. c The optic nerve sheath was measured at a depth of 3 and 5 mm posterior to the optic disc in the zoom mode. The depth marker was located at the vitreoretinal interface of the optic disc (Red inverted triangle), which was defined as 3 and 5 mm posterior to the globe. As shown in b, the pia mater (P) appeared as a dark structure fused with the optic nerve (N), the subarachnoid space (S) was the two hyperechoic striped bands, and the dura mater (D) showed as a dark line in-between the white retrobulbar fat and the hyperechoic striped bands. The optic nerve diameter (OND) was marked by the hyperechoic inner boundary on both sides (S1) and optic nerve sheath diameter (ONSD) was marked by the hyperechoic outer boundary on both sides (ONSDint, S2). The entire coronary transversal area of the optic nerve subarachnoid space (ONSSA) between 3 and 5 mm was outlined in the two hyperechoic striped bands (Yellow stars). D1 represented the external edge of the dura matter and ONSD (ONSDext).