Tom Marshburn, NASA, and Chris Hadfield, Canadian Space Agency (image) NASA/Johnson Space Center Share Print E-Mail Caption Expedition 34/35 Flight Engineer Tom Marshburn of NASA performs a tonometry eye exam on Chris Hadfield of the Canadian Space Agency in the Columbus module of the International Space Station. Tonometry measures intraocular eye pressure. Credit Photo credit: NASA Usage Restrictions None Share Print E-Mail Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.