Purpose: To evaluate ocular responses and visual performance after high-acceleration force exposure.
Methods: Fourteen men were enrolled in the study. A human centrifuge was used to induce nine times the acceleration force in the head-to-toe (z-axis) direction (+9 Gz force). Visual performance was evaluated using the ETDRS (Early Treatment of Diabetic Retinopathy Study) visual chart, and contrast sensitivity (CS) was examined before and after centrifugation. Ocular responses were assessed with biomicroscopy and topographic mapping after gravitational stress.
Results: Transient visual acuity reduction (0.02 +/- 0.04 logMar vs. 0.19 +/- 0.07 logMar VA; P < 0.05) and temporary ocular anterior segment reactions were observed immediately after centrifugation. These reactions included changes in corneal thickening (553.7 +/- 21.7 mum vs. 591.2 +/- 20.6 mum; P < 0.05), increasing anterior chamber depth (ACD; 3.19 +/- 0.26 mm vs. 4.53 +/- 0.34 mm; P < 0.05), and pupillary enlargement (3.54 +/- 0.73 mm vs. 5.76 +/- 0.61 mm; P < 0.05). The increase in ACD continued for 15 minutes after exposure to acceleration (3.19 +/- 0.26 mm vs. 4.39 +/- 0.27 mm; P < 0.05). Pupillary dilation was noted both 15 (3.54 +/- 0.73 mm vs. 5.56 +/- 0.67 mm; P < 0.05) and 30 (5.47 +/- 0.59 mm, P < 0.05) minutes after the gravitational stress. CS decreased significantly at low and medium spatial frequencies (1.5, 3, and 6 cyc/deg) and did not return to the baseline level by 30 minutes.
Conclusions: High-acceleration force may induce transient visual acuity reduction and temporary corneal thickening. Prolonged increase in ACD and pupillary dilation were also observed. The decrease in CS persisted for 30 minutes after centrifugation. The mechanisms underlying these observations are not clear, because there are no previous reports on this topic. Further studies are needed.