30° test.

A-scan (figure) or B-scan (not shown) ultrasonography is used to measure the optic nerve sheath diameter in primary (left) and eccentric gaze (right). A reduction in the nerve sheath diameter >20% is considered a positive result, strongly suggesting increased fluid around the optic nerve.

Image credit: Wang R, Kini A, Al Othman B, Lee AG. Pseudotumor cerebri and papilledema: an overview of this perplexing syndrome and its hallmark presentation. Glaucoma Today. 2019 Jan/Feb:34-46. Available online.