Ultrasound could be used to help detect and treat glaucoma - an eye disease which can lead to permanent blindness.

New research suggests that examining an eye with ultrasound while exciting it with audible sound waves will give an accurate reading of the fluid pressure behind the cornea.

"In glaucoma, the pressure inside the eye fluctuates greatly throughout the day," said Mardi Hastings, an associate professor of biomedical and mechanical engineering at Ohio State University.

"An ophthalmologist prescribes drugs based on a one-time pressure reading, so it's difficult to get the right dose of medicine to treat the glaucoma properly.

"If a patient had a way to monitor changes in pressure inside the eye, she could determine her normal eye pressure, know when the pressure deviates from that norm, and take medication accordingly."

Small loudspeaker

The painful condition is caused by too much fluid in the eye.

Currently the most common way to measure pressure inside the eye is to puff air at it. Another method involves prodding the anaesthetised eye with a tiny instrument and measuring the depth of the indentation.

But both methods can be uncomfortable.

Professor Hastings used a small loudspeaker and two ultrasonic transducers, one to transmit an ultrasonic wave to the eye and the other to receive the reflected ultrasonic wave from its surface.

She injected animal and human eyes from an eye bank with saline solution to mimic glaucoma and then exposed them to a continuous tone from the loudspeaker, causing them to vibrate.

The motion caused by the audible sound wave altered the ultrasound wave reflected from the eye.

Harmonise

An increase in fluid pressure in the eye makes the cornea stiffer. When the cornea increases in stiffness, the eye's response to sound waves changes.

The eventual goal is to develop a hand-held device that contains a small loudspeaker, ultrasonic transducers, and the electronics needed to measure the eye motion from the reflected beam.

Professor Hastings is currently trying to determine the best frequency of excitation to use for measuring fluid pressure inside the eye.

"There are frequencies the cornea likes that cause it to vibrate a little more. Knowing these frequencies would allow a patient to calibrate her pressure measuring device in order to get the most accurate reading."

"Using the technology would likely be more comfortable and less cumbersome to the patient," she said.