Effects of +3Gz, +2Gz, and -1Gz on Intraocular Pressure (IOP)

ABSTRACT

BACKGROUND: Pilots of tactical aircraft are exposed to sustained accelerations ranging from -1Gz to +9Gz. Pilots are routinely exposed to +2 and +3Gz. It has been known that chronic elevations in intraocular pressure (IOP) are associated with the development of visual impairments, which could lead to a damage of optic nerve fibers with subsequent visual field defects. This IOP alteration may be caused by body fluid shifts resulting from acceleration forces. The IOP, theoretically, will be increased under negative Gz acceleration resulting from cephalad shift of body fluid and should not be increased under positive Gz accelerations according to hydrostatic column effects. However, there is little research regarding intraocular pressure changes during acceleration forces. Therefore, this study was designed to evaluate IOP effects of exposure to +2 Gz, +3 Gz, and -1Gz environments. METHODS: Intraocular pressures were measured on 3 subjects (2 men and 1 woman) during +2Gz, +3Gz, and -1Gz centrifuge exposures on the Dynamic Environment Simulator (DES) centrifuge. Two IOP measurements were obtained with the Ocuton S self-tonometer at +1Gz (Pre-baseline), +2Gz, +3Gz, -1Gz, and again at +1Gz (Post-baseline). A total 60 measures were obtained under +1Gz, + 2Gz, + 3Gz, and -1Gz. RESULTS: The result showed that there was a significant difference in the means for percent change of IOP from pre-baseline to +2Gz, +3Gz, and -1Gz. The mean IOP increased by 19.5% during +2Gz acceleration when compared to pre-baseline (16.3 vs. 19.5 mmHg, P=0.0001). The mean IOP of +3Gz level was 30.2% higher than that of pre-baseline level (16.3 vs. 21.2 mmHg, P=0.0001). The mean of IOP increased 127.9% during -1Gz when compared to baseline values (16.3 vs. 37.1 mmHg, P=0.0001). However, there was no significant difference in IOP between pre-baseline and post-baseline (16.3 vs. 16.0 mmHg, P=0.4261). There were significant differences, in percent change from pre-baseline, among the +2Gz, +3Gz, and -1Gz conditions {F (2,18)=152.05, P=0.0001}. There was a significant difference in the means of IOP at +2Gz and -1Gz (19.5 vs. 37.1 mmHg, P=0.0001). There was a significant difference in the means of IOP at +3Gz and -1Gz (21.2 vs. 37.1 mmHg, P=0.0001). There was a marginal significance in the means of IOP at +2Gz and +3Gz (P=0.0321). CONCLUSION: The conclusion of this study was that significant increases in IOP were found during +2Gz and +3Gz as well as -1Gz when compared to pre-baseline IOP values. These findings suggest that a rise of IOP during +2Gz and +3Gz cannot be explained by the hydrostatic column effects that are associated with acceleration exposure.