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If fluid pressure inside the eye gets too high, the optic nerve can be damaged. Opticians measure this pressure using a device that blows a puff of air onto the eyeball and monitors the reaction. Canadian company Eric Technologies of Calgary (W0 03/82086/7) has patented a home test in which a vibrating pad rests on the eyelid and a sensor measures the delay between each movement of the pad and the vibration in the eye. This gives a rough indication of the fluid pressure inside.