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Flowmeter tests eyes in zero gravity

21 Mar 2003

NASA scientists probe changes in astronauts' vision with a laser Doppler flowmeter.

A research team from NASA is developing an optical measurement system to investigate mysterious changes in the eyesight of astronauts during spaceflights.

According to Rafat Ansari and colleagues at the Glenn Research Center, a significant number of astronauts have complained that their visual acuity changes when in orbit.

Although it is not known what causes this effect, the team suspects that changes in blood flow in the choroid (part of the eyeball that provides nutrients to the retina through a dense network of capillaries) caused by zero-gravity conditions may be responsible.

When combined with changes in the eye's intraocular pressure, this could alter the shape of the cornea or lens.

To test their theory, Ansari and the team have built a head-mounted laser Doppler flowmeter, which is based around a 100 µW continuous-wave source emitting at 780 nm. Late last year, the team carried out experiments on parabolic flights, in which the steep climb and subsequent dive of an aeroplane causes temporary zero-gravity conditions.

The flowmeter measured the speed, volume and flow of choroidal blood under zero gravity conditions in five volunteers on board the flights. The team found a consistent pattern of increased speed, volume and flow of red blood cells under the conditions, but vibration in the aeroplane caused excessive noise, limiting the reliability of results. They are now looking to improve their apparatus and alleviate this problem.

The Glenn team presented their findings during the BIOS conference at Photonics West in San Jose earlier this year.

Michael Hatcher is technology editor of Opto and Laser Europe magazine.

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