Blast Exposure Induces Ocular Functional Changes with Increasing Blast Over-pressures in a Rat Model

Purpose: Blast-related brain and ocular injuries can lead to acute and chronic visual dysfunction. The chronic visual consequences of blast exposure and its progression remain unclear. The goal of this study is to analyze ocular functional response to four levels of blast exposure and identify a threshold of blast exposure leading to acute and chronic visual dysfunction. Methods: Anesthetized adult male Long-Evans rats received a single-blast exposure at a peak overpressure of 78, 117, 164 or 213 kPa, delivered by a compressed air-driven shock tube. Clinical eye examination, intraocular pressure (IOP), flash electroretinography (fERG) and spectral-domain optical coherence tomography (SD-OCT) images were assessed prior to, and at multiple time points post exposure. Results: No abnormal fERG were observed for the two lowest-level blast groups (78 kPa or 117 kPa). For the 164 kPa group, the a- and b-wave amplitudes of the fERG were decreased at 3 days postexposure (p = 0.009 for a-wave, p = 0.010 for b-wave), but recovered to baseline levels by 7 days post-exposure. The IOP was unchanged for the 117 kPa and 164 kPa groups. The 78 kPa group demonstrated a small transient increase during week one (p = 0.046). For the highest blast group (213 kPa), the IOP was significantly elevated immediately post-exposure (p = 0.0001), but recovered by 24 hr. A bimodal depression in the fERG a- and b-wave amplitudes was observed for this group: the amplitudes were depressed at day 3 post-exposure (p = 0.007 for a-wave, p = 0.012 for b-wave), and recovered by day 7 post-exposure. However, the fERG amplitudes were once again depressed at week 8 post-exposure, suggesting a chronic retinal dysfunction. All retinae appeared normal in SD-OCT images. Conclusions: Our study demonstrates that a single-blast exposure may result in acute and chronic fERG deficit, and traumatic IOP elevation. Noninvasive functional tests may hold promise for identifying individuals with a risk for developing chronic visual deficits, and indicating a time window for early clinical diagnosis, rehabilitation, and treatment.