Some patients have increased intracranial pressure which leads to swelling of the optic nerve and headaches. It can also lead to visual loss. We can measure the amount of fluid behind your eye through ultrasound. This is a painless test which involves putting an anesthetic on the eye and an ultrasound probe next to it. We do a measurement with you looking straight ahead and then in 30 degrees of abduction. We compare the measurement of the optic nerve shadows. The ultrasound passes through one side of the optic nerve and reflects back and then through the next interface in the sheath of the optic nerve, followed by fluid and the nerve itself, then fluid on the other side, and finally optic nerve sheath again. There is a spike seen at each of the interfaces. This tells us how wide the optic nerve is. As the eye turns, the optic nerve kinks when fluid builds up. By relieving this fluid during optic nerve sheath decompression, visual function can be restored.