Abstract:

Objective To investigate the impact of different ultraviolet(UV) irradiated intensity and duration on the stability of tear film  and corneal tissue of rats. Design Experimental study. Participants 50 male SD rats. Methods Fifty healthy male SD rats were randomly divided into the normal control group, test group A, B, C, D. Tested rats received UV irradiation three times a week for 6 weeks. Each irradiation had one-day interval. Every time，the rats in the test group A and C were exposed to the UV of 142 μw/cm2 for 8 min, and 12 min respectively. The rats in the test group B and D were exposed to the UV of 94 μw/cm2 for 12 min, and 18 min respectively. The results of examination at 14 d, 28 d, 42 d after exposure to UV irradiation were recorded. The examinations include slit lamp observation and photograph, sodium fluorescein dye; tear film break-up time (BUT) and basal tear secretion(Schirmer’s-I test, SIt). The rats were sacrificed by overdose of chloral hydrate and the corneal tissue sections were made. Main Outcome Measures Changes of morphological structure of conjunctiva, cornea and the tear film, corneal fluorescein staining scores, BUT, basic tear secretion, corneal tissue section observation. Results On slit lamp observation, higher-intensity group showed a earlier and severer conjunctiva congestion, corneal edema, and corneal opacity. Higher-intensity group appeared characteristic corneal neovascularization, while low-intensity group was characterized by the changes of the quality and quantity of tear-film. Comparison of Group A and C showed that longer-irradiation-duration group had a similar tendency with higher-intensity group, moreover, it appeared characteristic stripped ulcer in palpebral area. Fluorescein staining test showed the result of the control group was negative, group A was positive, group B was weakly positive, and group C and D was strongly positive. BUT at 42th day of group A, B, C, D were significantly lower than the control group (all P<0.01). SIt in 42th days of group A, B, C, D were significantly higher than the control group (all P<0.01). Tissue sections showed that higher-intensity group (group A and group C) appeared corneal neovascularization, reduced density of endothelial cell, disordered stroma fibroblasts. While lower-intensity group with shorter irradiation-time(group B) showed thickened epithelium, and lower-intensity group with longer irradiation-time (group C) showed corneal neovascularization and disordered stroma fibroblasts. Conclusions Ultraviolet irradiation can cause ocular surface damage, which contains conjunctival congestion, corneal epithelium damage, the changes of tear-film quality and quantity. These occurred earlier and severer with increasing irradiation intensity or increasing duration of irradiation. (Ophthalmol CHN, 2017, 26: 96-100)

Key words: ultraviolet rays, the tear film, corneal