Background Recent research on macular diseases has prompted investigations into the condition of the intersection between the inner and outer segments (IS/OS), and its relationship with retinal photoreceptor abnormalities. Because the correlation between optical coherence tomography (OCT) images and histopathology is unclear, the authors compared them in an N-methyl-N-nitrosourea (MNU)-induced photoreceptor degeneration rat model.

Methods MNU (60 mg/kg), which is toxic to photoreceptors, was injected in 12 Brown Norway rats. After MNU administration, three rats were used per histopathological study 3 h, 6 h, 24 h and 1 week after the injections. Two healthy rats served as controls. OCT images were taken before euthanisation.

Results 3 h after the MNU injections, the IS and OS were oedematous, but the IS/OS borderline was recognised histopathologically, and the IS/OS was depicted on the OCT images. Six hours after injections, the OS were preserved, but the IS structures were destroyed or partially disorganised histopathologically, and the IS/OS was not observed on the OCT images. Twenty-four hours after the injections, the IS and OS were totally disorganised histopathologically, and the IS/OS was not depicted on the OCT images.

Conclusion The IS structure might be the origin of the IS/OS on OCT images.