Ocular responses and visual performance after emergent acceleration stress.

Purpose: To evaluate visual function after emergent acceleration stress.

Methods: Sixteen subjects were enrolled in this study. Human ejection seat trainer was used to induce six times gravitational force in the head-to-toe (z-axis) direction (+6 Gz). Visual performance was evaluated using the visual chart and contrast sensitivity (CS) at indicated times. Ocular reactions were assessed with biomicroscopy and topographic mapping.

Results: Temporary visual acuity reduction (0.02 ± 0.05 vs. 0.18 ± 0.08 logMAR visual acuity [VA]; P < 0.05) and ocular reactions were observed after ejection. These reactions included changes in increasing anterior chamber depth (ACD; 3.18 ± 0.29 vs. 4.48 ± 0.32 mm; P < 0.05) and pupillary dilation (PD; 3.56 ± 0.72 vs. 5.64 ± 0.56 mm; P < 0.05). The ACD deepening continued at 15 minutes (4.37 ± 0.26 mm; P < 0.05), and PD persisted at 30 minutes after the gravitational stress (5.42 ± 0.54 mm, P < 0.05). CS decreased significantly at all spatial frequencies immediately after ejection. However, CS returned to the initial range at high spatial frequency by 30 minutes.

Conclusions: Emergent acceleration force induces significant ocular responses and visual fluctuation. Prolonged ACD deepening (>15 minutes) and PD (>30 minutes) were noted, but cornea and refraction remain stable. CS at all spatial frequencies revealed remarkable reduction immediately after ejection, and recovered to baseline levels within 30 minutes only at high spatial frequency. Neuroretinal function may involve visual fluctuation after acceleration stress, because visual fluctuation corresponds with the characters of neuroretinal function. However, further studies are necessary.