Airsoft Gun–Related Ocular Injuries: Novel Findings, Ballistics Investigation, and Histopathologic Study




Purpose


To describe the ocular injuries related to airsoft gun bullets, investigate the ballistics of airsoft bullets, record real-time impact of the bullets on an eye, and investigate the histopathologic changes within the cornea after being hit by an airsoft gun bullet.


Design


Retrospective, interventional case series and experimental animal study.


Methods


All consecutive cases of patients with airsoft gun–related ocular injuries during 2006 to 2008 were included in this study. Porcine eyes were used for high-speed video photographs of bullet impacts. Rabbit eyes were used for the histopathologic investigation. All patients were treated in the Department of Ophthalmology at Soroka University Medical Center, Beer-Sheva, Israel. Laboratory investigations were performed at Ben-Gurion University of the Negev, Beer-Sheva, Israel. The main outcome measures were ocular injuries of the patients, ballistics of the airsoft bullets, nature of corneal deformation upon impact, and corneal histopathologic changes after the hit.


Results


Fifty-nine patients with a mean age of 9.8 ± 3.8 years (range, 2.8 to 26 years) were examined; 49 were male (83.1%). The ocular injuries included hyphema, corneal edema, corneal erosion, traumatic mydriasis, and posterior segment involvement. A novel, “donut” form of corneal erosion was seen and also demonstrated by the histopathologic investigation. Substantial anterior segment deformation was recorded in real-time using the high-speed video camera.


Conclusions


Airsoft gun injuries affect mainly young men and can be visually threatening. Typical ocular injuries along with a unique form of corneal erosion can be seen.


Airsoft guns (also called “softgun”) are 1:1 scale replicas of actual firearms and were first designed and marketed in the United States about 35 years ago. Airsoft guns are plastic pistols that shoot hard round plastic bullets with a diameter of 6.0 mm ( Figure 1 ). The bullets are available in 3 weights (0.12 g, 0.20 g, and 0.25 g), and can also be in the form of “mini-paintballs.” The airsoft bullets are much lighter than the lead bullets used in BB guns (0.52 to 1.6 g). The guns use the direct force of a spring coil or compressed gas to fire the bullets. The airsoft bullets are made of a very hard and noncompressible plastic material and thus do not absorb energy. The muzzle velocity of a professional airsoft gun can reach over 120 m/s, but most commercially available airsoft guns reach a muzzle velocity of about 70 to 90 m/s. The effective flight range of an airsoft bullet is 30 to 50 m. In comparison, BB gun bullets reach speeds up to 200 m/s and have an effective flight range of about 150 m.




FIGURE 1


A common airsoft gun with 3 types of bullets: 0.2-g standard bullet (yellow), “mini-paintball” bullets (red), and 0.12-g standard bullets (green).


Airsoft guns have gained popularity since they are relatively cheap, can be purchased without age restrictions, and look real. Many authorities have restricted the use and sales of these guns, but nevertheless they can still be easily purchased. Although it is well recognized that conventional BB guns are vision threatening, the potential ocular hazards of airsoft guns do not seem to be sufficiently recognized. A literature search of English-language reports of airsoft ocular injuries finds a limited number of studies. In all reports, the typical victim of the airsoft gun injury is a young male subject. Ocular injuries can be found in both the anterior and posterior segments, with corneal erosion, corneal edema, hyphema, traumatic mydriasis, and retinal edema being the most common findings.


While treating patients with airsoft gun injuries in Soroka University Medical Center, we inspected a unique “donut” form of corneal erosion that has not been previously described. This led us to investigate the nature of airsoft bullet impact.


There are 4 purposes for this study: to describe the ocular injuries by airsoft gun bullets with emphasis on the unique corneal erosion; to investigate the ballistics of airsoft bullets; to record the impact of the bullet in real time; and to study the histopathologic changes within the cornea after a bullet hit. To our knowledge, no such comprehensive report has previously been published on airsoft-related ocular injuries.


Methods


Case Series


Clinical records of all consecutive cases of ocular injuries from airsoft gun bullets treated in the Department of Ophthalmology at Soroka University Medical Center, Beer-Sheva, Israel, during 2006 to 2008 were reviewed. This center is the only tertiary hospital in a region of approximately 0.8 million people.


Complete ocular examination was performed in each case. We registered the patients’ age, gender, symptoms, and ocular findings. Initial and final follow-up examinations included visual acuity, slit-lamp biomicroscopy, applanation intraocular pressure (IOP), and indirect ophthalmoscopy. Patients were scheduled, as needed, for further additional eye examination. Treatment profile and follow-up time were also documented.


Ballistic Investigation


Ballistic investigation of the airsoft gun bullets was performed in the Department of Mechanical Engineering at Ben-Gurion University of the Negev, Beer-Sheva, Israel. Regular 0.12-g bullets were used in this section of the study. The bullet flight was captured by a high-speed camera system in which the illumination is double-frequency neodymium-doped yttrium aluminum garnet laser (Lee Laser Inc, Orlando, Florida, USA) pulsed at 10 kHz. The camera is loaded with standard 35-mm 400 ASA TMAX film (Eastman Kodak Co., Rochester, New York, USA). At the time when the bullet leaves the barrel, a trail of pulses illuminates the bullet. A prism positioned in the camera deflects each pulse to a different position on the film and produces an image. To trigger the illumination, a He-Ne laser (Melles Girot, Rochester, New York, USA) and photo-detector were used. The photography sequence was controlled by a standard personal computer and timing card (T-IO-10; National Instruments, Austin, Texas, USA). About 25 images can be captured on each run. The bullet position is plotted vs time, and the velocity is then calculated.


Real-Time Recording of Bullet Impact


Real-time recording of impact of the airsoft gun bullets was performed in the Department of Mechanical Engineering at Ben-Gurion University of the Negev, Beer-Sheva, Israel. Porcine eyes were fixated to a polyethylene surface. The eyes were pressurized to physiologic pressure. Tests were conducted by firing 0.2-g bullets from a distance of 0.2 m. A high-speed video camera (Motion Scope PCI 8000sc; Redlake Imaging Corp, Morgan Hill, California, USA, with a Pentax Cosmicar TV 25-mm lens) was pointed toward the porcine eye and recorded the impact event at 4000 frames per second.


Histopathologic Investigation


Histopathologic investigation was performed in the Pathology Institute at Soroka University Medical Center, Beer-Sheva, Israel. Four rabbits (weight range, 3200 to 3700 g) were anesthetized with an intravenous mixture of ketamine 35 mg/kg (Vetalar; Fort Dodge Laboratories Inc., Fort Dodge, Iowa, USA) plus xylazine 5 mg/kg (XYL-M2 Veterinary; V.M.D. N.V., Arendonk, Belgium). Drops of benoxinate hydrochloride were also instilled on the rabbit eyes to achieve both general and local anesthesia. A 0.12-g bullet was then shot into the center of the rabbit cornea in both eyes. The eyes were enucleated and sent for histopathologic investigation by standard hematoxylin-eosin stains. After enucleation of both eyes the rabbits were overdosed with intravenous barbiturates.




Results


Case Series


Fifty-nine patients were included in this study ( Table 1 ); all of them were accidentally hit directly in 1 eye from airsoft gun bullets at distances of 0.5 to 3 meters. The patient admission took place 1 hour to 1 day after the injury. Forty-nine patients were male (83.1%). The mean age of the patients was 9.8 ± 3.8 years (range, 2.8 to 26 years). Mean initial best-corrected visual acuity (BCVA) was 0.66 (20/30 Snellen). Among anterior segment injuries, the most common ocular injury was hyphema (66.1%), followed by corneal edema (61.0%), corneal erosions (59.3%), and traumatic mydriasis (25.4%). Elevated IOP and traumatic cataract were seen in 1 patient (1.7%). Hospitalization was required in 6 cases (10.2%).



TABLE 1

Demographics and Ocular Findings in Patients Suffering From Airsoft Gun Injuries








































































Number of eyes 59
Number of patients 59
Age (years), range 9.8 ± 3.8, range 2.8 to 26
Gender
Male (%) 49 (83.1%)
Female 10 (16.9%)
Affected eye
Right (%) 34 (57.6%)
Left (5) 25 (42.4%)
Mean initial BCVA 0.66 (20/30 Snellen)
Ocular findings (%)
Anterior segment
Hyphema 66.1%
Corneal edema 61.0%
Corneal erosions 59.3%
of those, with “donut” pattern 40.0%
Traumatic mydriasis 25.4%
Elevated IOP 1.7%
Traumatic cataract 1.7%
Posterior segment
Retinal edema 22.0%
Retinal & vitreous hemorrhage 2.1%
Mean final BCVA 0.8 (20/25 Snellen)

BCVA = best-corrected visual acuity; IOP = intraocular pressure.


As mentioned, the most common findings were corneal edema, hyphema, and corneal erosions. The corneal erosions were usually slightly larger than 6 mm (the bullet diameter) with substantial corneal stromal edema ( Figure 2 , Top left and right). Of the patients with corneal erosions, 40.0% showed a very unique shape of corneal erosion, which we had not encountered before. In the center of the erosion was an island of corneal epithelium that did not stain with fluorescein ( Figure 2 , Middle left and right). We described these erosions as “donut erosions” because of their appearance. Some of these donut erosions had a remaining “hinge” of corneal epithelium on one side that had not yet detached from the periphery ( Figure 2 , Bottom left and right), giving them the shape of an epithelial flap. Later in follow-up, usually in the first hours after the hit, the epithelium island fell, leaving a “regular” corneal erosion. This unique and unusual form of corneal erosion led us to further search for the exact nature of this kind of injury.




FIGURE 2


Three forms of corneal erosions caused by airsoft gun bullet. (Top left) “Regular” corneal erosion approximately the size of the airsoft gun bullet; marked stromal edema and hyphema are seen (Case 8). (Top right) Same eye with fluorescein stain. (Middle left) “Donut erosion” pattern with marked stromal edema (Case 1). (Middle right) Same eye with fluorescein stain. Note that the central island of the corneal epithelium does not stain. (Bottom left) “Donut erosion with a hinge” pattern (Case 7). (Bottom right) Same eye with fluorescein stain. The “hinge” is demonstrated and the erosion has a temporal epithelial flap.


Injuries of the posterior segment included retinal edema in 22.0% of the patients and retinal hemorrhages and mild vitreous hemorrhage in 2.1%. One patient (1.7%) developed traumatic cataract but continued his follow-up at a different institution. Mean follow-up time was 7.6 months. Mean final BCVA was 0.8 (20/25 Snellen), which is significantly better than the initial BCVA ( P < .0001). The final BCVA was fair even in cases with initial BCVA of light perception and presence of corneal erosion, corneal edema, hyphema, and retinal edema and retinal hemorrhages.


Ballistic Investigation


Using the method described previously, a series of bullet positions over time was obtained ( Figure 3 , upper images, Top left and right) and the bullet position was plotted vs time ( Figure 3 , Bottom right, plot). A linear velocity was observed with a calculated value of 73 ± 1 m/s. Over longer distances the bullet will gradually slow because of drag, but in the practical range of the airsoft gun (several meters), the velocity decrease would be insignificant.


Jan 17, 2017 | Posted by in OPHTHALMOLOGY | Comments Off on Airsoft Gun–Related Ocular Injuries: Novel Findings, Ballistics Investigation, and Histopathologic Study
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