3-D eye movement measurements on four Comex's divers using video CCD cameras, during high pressure diving

Previous studies have shown the vulnerability of the vestibular system regarding barotraumatism (1) and deep diving may induce immediate neurological changes (2). These extreme conditions (high pressure, limited examination time, restricted space, hydrogen-oxygen mixture, communication difficulties etc.) require adapted technology and associated fast experimental procedure. We were able to solve these problems by developing a new system of 3-D ocular movements on line analysis by means of a video camera. This analyser uses image processing and forms recognition software which allows non-invasive video frequency calculation of eye movements including torsional component. As this system is immediately ready for use, we were able to realize the subsequent examinations in a maximum time of 8 min for each diver: oculomotor tests including saccadic, slow and optokinetic traditional automatic measurements; vestibular tests regarding spontaneous and positional nystagmus, and reactional nystagmus to the pendular test. For pendular induced nystagmus we used appropriate head positions to stimulate separately the lateral and the posterior semicircular canal, and we measured the gain by operating successively in visible light and complete darkness. Recordings were done during a simulated onshore dive to an ambient pressure corresponding to a depth of 350 m. The above examinations were completed on the first and last days by caloric tests with the same video system analyser. The results of the investigations demonstrated perfect tolerance of the oculomotor and vestibular systems of these 4 divers thus fulfilling the preventive conditions defined by Comex Co. We were able to overcome the limitations due to low cost PC computer operation and cameras (necessity of adaptation to pressure, focus difficulties and direct light exposure eye reflexions). We still have on line accurate measurements even on the torsional component of the eye movement. Due to this technological efficiency we also present some mathematical aspects of the software.