Visual function after acoustic blast overpressure (ABO) injury: Effects of antioxidants and blast frequency

Abstract

Purpose : ABO exposure causes long-term retinal function and structure deficits. Here, we compared the protective effects of antioxidant-enriched diets on visual function in rats exposed to different ABO conditions.

Methods : Adult male Long-Evans rats were exposed to ABO (63kPa, 190+ db-SPL) directed at one eye, either 1x or 2x (1 mo apart). One month prior to first blast exposure, rats were randomized to 1 of 3 dietary groups: “Normal” (2016 Teklad Global 16% protein rodent diet; n=11-20); “Red” (Normal diet enriched with 2% cholesterol + Vitamins E&C + Na-selenite; n=4-8); or “Green” (Normal diet enriched with 0.05% (w/w) multifunctional antioxidant (JHX-4); n=4-8). Non-ABO-exposed, age-matched rats fed “Normal” diet served as controls (n=28). Both eyes of animals were tested at 2 and 4 mo post-blast for spatial frequency (SF) and contrast sensitivity (CS) thresholds [optomotor response] and retinal function [electroretinogram (ERG)]. Statistical analysis: two-way RM ANOVA (p<0.05).

Results : At 4 mo post-blast, SF was significantly reduced in ABO-exposed rats (1x and 2x) fed Normal diet relative to controls (Fig. 1a,b), but no statistical difference was observed between 1x vs. 2x ABO. Only Green diet provided protection for SF from 1x ABO (Fig 1a; p<0.05); for 2x ABO both Red and Green diets had significantly better SF than Normal diet (Fig 1b: Red, p<0.05; Green, p<0.01). At 4 mo post-blast, CS was reduced in both 1x and 2x blast groups, relative to controls (Fig. 1c,d;p<0.001). Both Red and Green diets were protective for CS in the 1x blast group (Fig 1c: Red, p<0.01; Green, p<0.001); no CS protection was observed in the 2x blast group. ERGs showed no differences across groups.

Conclusions : Antioxidant efficacy in protecting visual function varies with antioxidant type and number of blast exposures. Relationships between functional deficits and structural changes and the effects on the contralateral eye are being evaluated. Our results suggest different mechanisms may underlie the functional deficits with frequency of ABO exposure. Future research will focus on optimizing antioxidant regimens for protection of visual function from ABO-induced trauma.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.

 

Fig. 1: Visual function of 1x and 2x blast-exposed rats at 4 mo post-blast. Asterisks indicate post-hoc statistical significance: *p<0.05, **p<0.01, ***p<0.001.