The importance of vitreous humor in radiation-induced cataracts

The mechanism underlying radiation-induced cataracts has not been fully elucidated to date. An increase in oxidative stress induces cataract formation. Vitreous humor contributes to maintaining hypoxic conditions in the lens with its regulatory effect on oxygen pressure and the antioxidants it contains. This study aimed to investigate the impact of radiation-induced changes in vitreous humor on the lens, particularly its cataractogenic effect. Eight to ten-week-old New Zealand rabbits were used, and a single dose of 20 Gy of radiotherapy was applied to the left eye's vitreous humor, while the right eye served as the control group. Ophthalmological examinations were performed at monthly intervals during the three-month follow-up. At the end of the follow-up period, orbital magnetic resonance imaging (MRI) was conducted. Total oxidant and antioxidant levels were assessed using spectrophotometric methods within the vitreous humor samples. Cataracts developed in two of the eight surviving rabbits' irradiated eyes (25%). In orbital MRI, decreased signal intensity was observed in the left aqueous humor in non-contrast sequences (p = 0,03), while increased signal intensity was detected in late post-contrast sequences (p = 0,04). Total oxidant levels (p = 0,04) and oxidative stress index (p = 0,04) in the vitreous humor samples were significantly lower in the control group. These findings support that the alterations in the posterior structures of the eye due to radiation had effects on the anterior chamber and may contribute to the development of radiation-induced cataracts.