[Explosives-based vole traps-A novel injury pattern in the eye region]

A novel method for trapping voles is the use of pistol-like explosive tools loaded with bolt-action ammunition. When triggered the vole is killed by the very high gas pressure created. Accidental releases can result in facial and/or eye injuries. The aim of this work was to describe the injury pattern in the patient and to experimentally verify whether there is a risk of penetrating eye injuries.

Two emergency patients presented to our eye clinic with eye injuries after unintentional triggering of the explosive trap. Based on the new pattern of injury noted, experiments were performed on enucleated porcine eyes to determine the possible severity. For this purpose, a vole trap was clamped in a holder and loaded with a Cal. 9 × 17 mm cartridge in each case. In front of the muzzle opening, 3 pig eyes each were fixed on Styrofoam at a distance of 20, 40, 60 and 80 cm. The foreign body indentations in the cornea were visualized and measured by spectral domain optical coherence tomography (SD-OCT). The pig eyes were then dissected and searched for foreign bodies using microscopy. The SD-OCT images of an injured patient were also included for human comparison.

On patient examination, in addition to the usual fine gunshot marks on the face and conjunctiva/eye area, wax-like, larger and heavier particles of approximately 0.1-0.2 mm in size were found, which originated from the cartridge end cap. Removal of these foreign bodies, some of which were injected more deeply into the cornea, conjunctiva, and tenon, is much more difficult and extensive than in usual blast trauma. There was no evidence of intraocular foreign bodies in either patient. Likewise, no intraocular foreign bodies could be detected experimentally in any pig eyeball (n = 12). Remnants of the wax-like cartridge end were found deeply penetrating into the corneal stroma. The maximum penetration depth measured against the total corneal thickness was 46% at 20 cm device distance and decreased with greater distance to the vole trap (penetration depth at 40 cm at 37%, at 60 cm at 28% and at 80 cm at 19%). For comparisons on the human eye, a penetration depth of 54% was measured at a distance of about 40 cm. In pig eyes the number of foreign bodies per cm² decreased with increasing distance from the vole trap (mean: n = 174 foreign bodies, FB, at 20 cm distance, n = 46 FB at 40 cm, n = 23 FB at 60 cm, and n = 9 FB at 80 cm). The largest penetrating foreign bodies measured a mean of 383 ± 43 μm with a maximum of 451 μm.

New vole traps with gas-powered mechanisms result in larger deeply penetrating wax-like foreign bodies in the cornea, conjunctiva, and tenon of the eye, which are difficult to remove and only surgically possible. Despite the significant explosion during triggering, there was no evidence of penetrating ocular injury from the foreign bodies either in the patient or experimentally in the pig eyes. Safety goggles should be worn when handling the traps to avoid penetration of foreign bodies into the eye.