Background data of ophthalmological examination using slit-lamp and binocular indirect ophthalmoscopes in B6C3F1/Crl and C57BL/6J mice

<p>In ophthalmological examination in non-clinical safety studies, it is important to distinguish treatment-related findings from spontaneous lesions. However, few studies have reported the background data of ophthalmological examination in mice. In this study, ophthalmological examination using slit-lamp and binocular indirect ophthalmoscopes was conducted in B6C3F1/Crl and C57BL/6J mice, which are used in non-clinical safety studies, to obtain the background data for these strains. In both strains, ophthalmoscopy was conducted in 50 males and 50 females from 6 to 19 weeks of age. In addition, some representative animals with ophthalmoscopic findings were sacrificed at 21 weeks of age for ocular histopathological analysis. In B6C3F1/Crl mice, opacity of the lens posterior capsule was observed at 10 weeks of age or older (6.0% of males and 4.0% of females at 19 weeks of age) via slit-lamp examination. A dark-brown spot on the fundus (2.0% of males) was observed at 19 weeks of age via binocular indirect ophthalmoscopy. In C57BL/6J mice, the following findings were observed in animals of 6 weeks old or older via slit-lamp examination: at 6 weeks of age, anterior synechia of the iris (2.0% of females), opacity of the lens nucleus (16.0% of males and 22.0% of females), opacity of the lens posterior capsule (34.0% of males and 68.0% of females), brown spot on the lens posterior capsule (8.0% of males and 2.0% of females), and brown floater in the vitreous body (4.0% of males and 10.0% of females). The incidence of lens opacity increased with age: at 19 weeks of age, opacity (2.0% of males) and irregular surface (14.0% of males) of the anterior capsule and opacity of the posterior cortex (8.0% of females) were observed. In binocular indirect ophthalmoscopy, a red spot (2.0% of males) and a white spot (2.0% of males) on the fundus were observed in C57BL/6J mice of 6 weeks old or older. In addition, depigmented spots on the fundus were noted in 10-week-old mice (14.0% of males and 18.0% of females), and its incidence was higher at 19 weeks of age (38.0% of both males and females). Histopathologically, rupture of the lens posterior capsule was observed in the eyes with opacity of the lens posterior capsule. In conclusion, the incidence of spontaneous ocular lesions in slit-lamp and binocular indirect ophthalmoscopy were investigated in B6C3F1/Crl and C57BL/6J mice from 6 to 19 weeks old: some of them were different between strains. The results of the present study are considered useful for distinguishing treatment-related findings from spontaneous lesions in non-clinical safety studies in mice.</p>