Equipment and scanning
We used The Esaote QElaXto 2D sonography system (Esaote S.p.A., Genova, Italy) with SWE software sonoelastographic evaluations. A linear array probe of 6–9 MHz was used in the SWE examinations. The participants had a supine position with closed eyes during the examination. We applied the coupling gel between the eyelids of all the participants and instructed them not to move their eyes during the examination. We measured the optic nerve diameter (OND) for each eye between the external hypoechogenic borders of the optic nerve without hyperechogenic space surrounding that nerve by the B-mode US and then we applied SWE without compression. We standardized the examination technique based on literature.9,13,14In addition to the optic nerve, we obtained the measurements of the perineural area and optic disc by SWE. We used the transverse plane from inside the equator of the eyeball and longitudinal axis of the optic nerve for measurements and then saved static images.