Neutrophil infiltration induced by low-level single and repeated blast exposures in the rat cornea

Abstract

Purpose: Ocular injuries are commonly observed in victims of explosive blast, afflicting more than a fourth of blast survivors. Injuries to the eye are the fourth most common military-related injury. However, research regarding the precise mechanisms of corneal injury by primary blast has been limited to descriptions of gross pathology. The purpose of this study is to characterize the effects of single or repeated exposure to low-level blast exposure for rat corneal tissue.

Methods: A compressed-air driven shock tube was used to expose Long-Evans rats to blast waves of peak overpressure 68.0 ± 2.7 kPa and positive peak duration 2.8 ± 0.1 ms. For repeated blast exposure, rats were exposed once daily for five consecutive days then euthanized on day 5, one hour after the last blast exposure. Rats subjected to a single blast exposure were euthanized 5 days following the one blast exposure, and rats not exposed to blast were included as controls. Corneal images were taken using a slit lamp after every blast exposure. Eyes were collected and histology was performed with hematoxylin and eosin staining. Corneas were examined for neurtrophil infiltration.

Results: Infiltrated neutrophils were observed in the corneal stroma layer in rats exposed to both single blast exposure and repeated blast exposure. However, a significantly higher number of neutrophils were observed in the corneal stroma layer closer to the ciliary body of repeatedly exposed rats. Mild edema was observed via slit lamp in the cornea of rats exposed to repeated blast, but not single blast. Tissues from control animals not exposed to blast overpressure were negative for neutrophil infiltration and corneal inflammation.

Conclusions: Neutrophil infiltration in the corneal stroma layer close to the ciliary body was observed in response to blast exposure. The number of neutrophils increased with repeated blast exposure, suggesting a cumulative effect for even low-level blast exposure. For future studies we propose to investigate the precise mechanism of corneal wound by blast overpressure which will require a long term study to examine chronic effects such as scar formation after corneal injury.

Keywords: 484 cornea: stroma and keratocytes • 557 inflammation • 637 pathology: experimental