The use of three dimensional (3D) ultrasonography (3DUS) for optic nerve measurements has been described in normal eyes utilising coronal “C-scans.”1,2 This study demonstrates the use of 3DUS generated C-scans for optic nerve measurements in orbits with optic nerve sheath meningioma and compares those with measurements obtained from computed tomography (CT) scans. A 69 year old woman with a left optic nerve sheath meningioma was treated with external beam radiation therapy 6 years earlier. On 3DUS coronal C-scans, an optic nerve sheath diameter (ONSD) 3 mm behind the globe was measured to be 7.4 mm in the left eye (fig 1, top left) and 6.4 mm in the right (fig 1, top right). Figure 1 Case 1. The patient’s left (top left) and right (top right) optic nerve sheath diameters are shown …