Background Dimethylhydrazine is widely used as a liquid propellant for strategic missiles. As an exposed organ of the human body, the eyes are susceptible to its harm during operation. Therefore, it is crucial to study the hazards of eye contamination with Dimethylhydrazine.

Objective Detect the distribution of unsymmetrical dimethylhydrazine in various eye tissues and blood, observe the eye irritation response of unsymmetrical dimethylhydrazine and measure the pH changes in rabbit conjunctival sac and aqueous humor after unsymmetrical dimethylhydrazine poisoning.

Methods The rabbit eye toxicity model was divided into a 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 blood, the eye irritation response scores of each group were observed under a slit lamp microscope and use a fiber optic pH meter to measure the pH changes in the conjunctival sac and aqueous humor.

Results No unsymmetrical dimethylhydrazine was detected in any tissue of the normal control group's eyes. Within 1 hour after exposure, unsymmetrical dimethylhydrazine was detected in all tissues of the eyes, the highest content of unsymmetrical dimethylhydrazine was found in aqueous humor which was (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 (0.00, 000) , and the scores of tainted 1 h, 2 h, 1 d, 3 d, and 7 d groups were 2.75 (2.38, 3.00), 5.00 (4.63, 5.25), 6.00 (5.50, 6.00), 4.00 (4.00, 5.50), and 2.00 ( 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. The pH was 8.53 ± 0.10 and 7.67 ± 0.16 In 1h group, 8.50 ± 0.17 and 7.50 ± 0.09 in 2h group, 7.91 ± 0.13 and 7.16 ± 0.12 in 1d group, 7.87 ± 0.10 and 7.91 ± 0.17 in 3d group , 7.54 ± 0.12 and 7.60 ± 0.20 in 7d group. The pH difference were statistically significant (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.