The changes of corneal biochemical properties after simulated ejection on the ground

Ejection in high acceleration force may result in several physiologic responses and injuries. However, little is known about the effects of ejection on corneal rigidity and elasticity when pilots ejected from the cabinet after high +Gz acceleration. The aim of this study was to determine the changes of corneal biomechanical properties after simulated ejection. Thirty male pilots were enrolled in the study. The ejection seat training system at the Aviation Physiology Research Laboratory (Taiwan) was used to simulate ejection process at 8 times of gravitational force in head to toe Z-axis direction (+8 Gz force). Ocular Response Analysis (ORA) was applied to detect the dynamic bi-directional changes of cornea in the subjects who underwent simulated ejection. The related parameters were evaluated before ejection such as corneal hysteresis (CH), corneal resistance factor (CRF), and central corneal thickness (CCT). The bare visual acuity and refraction were also recorded. At instant, 15mins and 30mins after ejection, the parameters were detected as well. Two hours after ejection, the anterior chamber and relative position of lens were observed under the slit lamp. All the bare visual acuity and refractive errors remain unchanged during the study. There were no significant change of CH and CRF before and after ejection. However, the CCT increased significantly immediately after(548.5 ± 18.7 vs 590.8 ± 15.4, p<0.005) and 15 min after (548.5 ± 18.7 vs 587.5 ± 16.2, p<0.005) compared with the values before ejection. No hyphema, sub-location, or dislocation of the lens, or any rupture of the anterior lens surface were observed. After safe ejection on the ground, the main corneal biomechanical properties had no significant change. Besides, the refraction and bare visual acuity remained stable. We concluded that the rigidity and elasticity of the cornea, the stability of lens and the anterior segment of ocular structure were not apparently affected by high G-force. Nevertheless, our experiments were performed on the ground. During real high altitude ejection, true environmental factors such as windblast, low temperature, and hypoxia remained challenger to pilots. We need further studies in the future.