Effects of Primary Blast Overpressure on Retina and Optic Tract in Rats

Abstract

Blast has been the leading cause of injury, particularly traumatic brain injury and visual system injury, in combat operations in Iraq and Afghanistan. We determined the effect of shock tube-generated primary blast on retinal electrophysiology and on retinal and brain optic tract histopathology in a rat model. The amplitude of a- and b-waves on the electroretinogram (ERG) for both right and left eyes were measured prior to a battlefield simulation Friedlander-type blast wave and on 1, 7, and 14 days thereafter. Histopathologic findings of the right and left retina and the right and left optic tracts (2.8 mm postoptic chiasm) were evaluated 14 days after the blast. For two experiments in which the right eye was oriented to the blast, the amplitude of ERG a- and b-waves at 7 days post blast on the right side but not on the left side was diminished compared to that of sham animals (P = 0.005–0.01) Histopathologic injury scores at 14 days post blast for the right retina but not the left retina were higher than for sham animals (P = 0.01), and histopathologic injury scores at 14 days for both optic tracts were markedly higher than for shams (P < 0.0001). Exposure of one eye to a blast wave, comparable to that causing human injury, produced injury to the retina as determined by ERG and histopathology, and to both postchiasmatic optic tracts as determined by histopathology. This model may be useful for analyzing the effect of therapeutic interventions on retinal damage due to primary blast waves.

Repeated blast model of mild traumatic brain injury alters oxycodone self‐administration and drug seeking

“…Sham‐exposed rats were subjected to the same procedures but were placed outside the overpressure shockwave. Compared to other models using shockwave exposure inside the shock tube, the peak overpressure magnitudes from this model are slightly greater (Sajja et al ., ; DeMar et al ., ; Perez‐Garcia et al ., ; Wang et al ., ; Toklu et al ., ). However, peak shockwave overpressure is not the most appropriate injury metric.…”

Visual system pathology in humans and animal models of blast injury

“…A key requirement of blast models is the documentation of peak overpressures and their duration to ensure that the experimental design produces blast exposures comparable to what soldiers and civilians experience on the battlefield (Courtney & Courtney, ; Goldstein, McKee, & Stanton, ). Free‐field explosions (Hines‐Beard et al, ; Kuehn et al, ), shock tubes (DeMar et al, ; Petras et al, ), blast tubes (Elder, Stone, & Ahlers, ), and custom fabricated devices such as a modified nail gun (Kuehn et al, ) and a modified paint ball gun (Bricker‐Anthony, Hines‐Beard, & Rex, ; Bricker‐Anthony & Rex, ; Hines‐Beard et al, ; Guley et al, ; Heldt et al, ; Reiner et al, ) have been used to simulate primary blast injury. Advantages of the aforementioned custom fabricated models are low cost assembly, ease of use and the ability to isolate specific parameters of interest due to control of blast directed injury to the whole head (brain and eyes), specific regions of the cranium (brain only), and orbit (eye only).…”

“…Similar to humans, visual deficits from blasts in animals (Table ) can occur soon after blast and remain progressive. Several studies (Bricker‐Anthony et al, ; Bricker‐Anthony & Rex, ; DeMar et al, ; Mohan et al, ) highlight the importance of blast wave directionality in rodents. One study (Guley et al, ) in mice evaluating visual system deficits found that a single blast directed unilaterally onto a small portion of the cranium produced noticeable axonal damage.…”

“…This finding demonstrates that orientation with respect to the direction of blast waves can affect pathological outcome. Work by DeMar et al () suggests the lateral location of rodent eyes could be the reason for differences in ocular pathology. However, the occurrence of unilateral ocular injury in humans from eye‐directed blasts (Weichel et al, ) supports animal models of ocular injury.…”

“…Visual deficits, first detected as pathological changes in the central motor circuits controlling eye movement (Brahm et al, ; Greenwald, Kapoor, & Singh, ), are now known to include damage to the retina, leading several groups to focus on retinal pathology in animal models of blast injury (Bricker‐Anthony & Rex, ; Bricker‐Anthony et al, ; DeMar et al, ; Dutca et al, ; Greenwald et al, ; Mohan et al, ). Overall retinal ganglion cells (RGCs) and optic nerves are most vulnerable to injury (Choi et al, ; Dutca et al, ; Koliatsos et al, ; Mohan et al, ; Wang et al, ), although there are indications that photoreceptors and cells within the inner nuclear layer may incur delayed onset damage (Bricker‐Anthony & Rex, ; Dutca et al, ).…”