Experimental and numerical investigation of vision impairment in long-term exposure to microgravity

Recently researches have reported the ocular structural and functional changes observed in astronauts after long-duration space flight, which includes optic disk edema, globe flattening, choroidal folds, hyperopic shifts and reduction of near visual acuity. This syndrome, which is called the Visual Impairment/Intracranial Pressure (VIIP) Syndrome, is reported due to the alterations of translaminar pressure and some other factors (concentration of CO2, genotype, B-vitamin status, androgens, etc.) in microgravity or in space station. On account of the shortage of measurement and limit of sample size in space experiments, the study of VIIP Syndrome was difficult to make progress. In this research, numerical analysis combined with animal experiment were performed. In the animal experiment, hindlimb suspension (HLS) model was used to simulate the cephalic liquid shifts of Sprague-Dawley (SD) rats in microgravity, as well as fundus photography and optical coherence tomography (OCT) were executed to detect the ocular structural changes. For both the experimental group and the control group, the illumination, temperature and feeding were strictly controlled, well the watering was unrestricted, during the long-term hinlimb suspension. The ocular structural changes and the physiological index including weight and intraocular pressure (IOP) were evaluated. A numerical model of eye was established, then finite element analysis was performed to study the biomechanical response of ocular structure due to the changes of translaminar pressure. We observed that the changes of the ocular structure in rats after the long-term hindlimb suspension were consistent with the finite element simulation results. The findings in this research showed the significance of animal experiment and numerical analysis for the study of VIIP Syndrome.