Choroidal changes after intravitreal injection of interferon alpha-2b.

Intravitreal injection of interferon alpha-2b (IFN-alpha 2b) is used to treat uveitis but its effect on the choroid is unknown. We histologically evaluated the choroidal changes after intravitreal injection of IFN-alpha 2b. We compared histological samples of IFN-alpha 2b-injected eyes to eyes with lipopolysaccharide (LPS)-induced uveitis and eyes injected with balanced salt solution (BSS) as controls. Rabbit eyes received intravitreal injections of BSS, IFN-alpha 2b, or LPS, and enucleation was done seven days later. Choroidal changes were evaluated on histological cut sections. The thickness of the choroid was measured in micrometer and the severity of inflammation was scored. The mean maximum choroidal thickness was significantly greater in the IFN-alpha 2b group in comparison to the LPS and BSS groups (P < 0.001). The mean minimum choroidal thickness was also significantly greater in the IFN group compared to the BSS group (P = 0.009). The observed changes were mainly due to vasodilation rather than interstitial fluid retention or inflammation. Mild inflammatory cell infiltration was observed in the choroid of four eyes in the IFN group and of three eyes in the LPS group. No inflammation was seen in the control group. The difference in inflammatory cell infiltration between the LPS and IFN groups was not statistically significant. Significant choroidal hyperemia was present after injection of IFN-alpha 2b. This fact may suggest for some pharmacological applications of IFN-alpha 2b when increased choroidal circulation is needed. However, further studies are required to elucidate the mechanisms involved. Impact statement Type I interferons are proteins that are naturally secreted by cells in response to certain stimuli. They are approved for medical use to regulate immune responses in many disease states. Our findings of increased choroidal circulation after treatment of the eye with interferon alpha-2b indicate a possible effect of this cytokine on blood circulation. This is a novel finding that needs further investigation to elucidate mechanisms and applications.