Background Dimethylhydrazine is widely used as a liquid propellant for strategic missiles, and the eyes, as the exposed organs of the human body, are susceptible to its damage during operation.

Objective To detect the distribution of dimethylhydrazine in various tissues and blood of the eyes, observe the irritant response of dimethylhydrazine to the eyes, and measure the changes in pH values of the rabbit's conjunctival sac and aqueous humor after exposure to dimethylhydrazine.

Methods The rabbit eye toxicity model was divided into normal control group and groups 1 h, 2 h, 1 d, 3 d, and 7 d after exposure to unsymmetrical dimethylhydrazine. Gas chromatography-mass spectrometry was used to detect the content of unsymmetrical dimethylhydrazine in the eye and the blood, the eye irritation response scores of each group were observed under a slit lamp microscope and a fiber optic pH meter was used to measure the pH changes in the conjunctival sac and aqueous humor.

Results No levels of dimethylhydrazine were detected in the normal control group's ocular tissues. However, dimethylhydrazine was detected in all ocular tissues 1 hour after exposure, with the highest concentration in aqueous humor reaching (716.23 ± 23.71) mg/kg; After 2 hours some residual dimethylhydrazine was still present, but the content was significantly reduced compared to 1 hour (P＜0.001). However, no dimethylhydrazine was detected in various tissues of the eyes at 1 d, 3 d, and 7 d after exposure, and no dimethylhydrazine was detected in the blood. The normal control group had a rabbit eye irritation response score of 0.00 (IQR: 0.00 - 0.00), while the groups exposed to dimethylhydrazine for 1 hour, 2 hours, 1 day, 3 days, and 7 days had scores of 2.75 (IQR: 2.38 - 3.00), 5.00 (IQR: 4.63 - 5.25), 6.00 (IQR: 5.50 - 6.00), 4.00 (IQR: 4.00 - 5.50), and 2.00 (IQR: 1.50 - 2.00), respectively. The difference in eye irritation response scores among different groups was statistically significant (χ²=33.11, P＜0.001). The pH of the conjunctival sac and aqueous humor in the normal control group of rabbits was 8.34 ± 0.14 and 8.60 ± 0.26, and they were 8.53 ± 0.10 and 7.67 ± 0.16 in the 1 h group, 8.50 ± 0.17 and 7.50 ± 0.09 in the 2 h group, 7.91 ± 0.13 and 7.16 ± 0.12 in the 1 d group, 7.87 ± 0.10 and 7.91 ± 0.17 in the 3 d group , 7.54 ± 0.12 and 7.60 ± 0.20 in the 7 d group, with statistically significant differences (P＜0.001).

Conclusion Unsymmetric dimethylhydrazine can quickly penetrate into various tissues in the anterior segment of the cornea and reach the posterior segment of the retina, with the highest content in aqueous humor. However, the metabolism rate of unsymmetrical dimethylhydrazine is also very fast. Unsaturated dimethylhydrazine propellant has a mild irritating effect on eye tissue. The propellant grade solution exhibits weak alkalinity, and the pH changes in the conjunctiva and aqueous humor after eye infection are related to metabolic infiltration into the anterior chamber and an inflammatory response after tissue damage in the anterior segment of the eye.