An air- and spring-powered gun that propels table salt at a high velocity is now commercially available. The product's marketing and delivery may appeal to children due to the toy-like appearance of the gun (Figure 1). There is concern that children may point this at themselves or others and cause significant ocular trauma, potentially penetrating the eye. Globe penetration could pose a unique problem because salt would be expected to dissolve on contact with the cornea or anterior chamber. It is important to identify characteristics of these corneal injuries and determine therapeutic options to treat these complications. There are currently no publications on this specific mechanism of ocular injury.
Example of an air-powered salt gun (Bug-A-Salt; Skell Inc., Santa Monica, CA).
Two eyes from the same donor deemed unsuitable for transplantation were used to evaluate the extent of injury from an air-powered salt gun (Bug-A-Salt; Skell Inc., Santa Monica, CA). The globes were from a 63-year-old woman who died of respiratory failure. Both globes were stored in normal saline solution and were warmed to room temperature (approximately 72 degrees). The globes were wrapped circumferentially in 4 × 4 gauze to allow them to be secured in a mount composed of a foam cup attached to a board. The eyes were examined with a portable slit lamp prior to injury by the air-powered salt gun.
The air-powered salt gun was filled with table salt and placed 6 inches from the eye. This distance was chosen to simulate accidentally pulling the trigger at close range while looking down the barrel or pointing it toward the face of another individual. The gun was then fired, aiming directly for the center of the cornea. The left eye was prepared in a similar fashion but had cooled to ambient temperature (approximately 51 degrees) at the time of injury.
The slit-lamp examination prior to using the air-powered salt gun revealed small paracentral corneal abrasions in each eye, along with corneal edema and Descemet's folds. Examinations were performed with a portable slit lamp immediately after the air-powered salt gun was fired and reevaluated in the clinic with a table-mounted slit lamp (Haag-Streit BM 900, Mason, OH) approximately 48 hours after injury.
Examination of the right eye with the slit lamp revealed a large corneal abrasion and one salt particle that appeared to penetrate the cornea and travel to Descemet's membrane. The eye was assessed by Seidel test using fluorescein strips, but no leakage was identified with or without applied pressure. The epithelial defect encompassed approximately 70% of the corneal surface (Figure 2) and involved much of the conjunctiva.
Fluorescein stain of the right eye following air-powered salt gun injury.
The examination of the left eye revealed similar findings. A large corneal abrasion was noted with epithelial sloughing. There was one large salt granule embedded in the corneal stroma. Two salt granules appeared to travel at full thickness through the cornea, creating Descemet's scrolls, and appeared to be located within the anterior chamber. Seidel testing with fluorescein strips revealed a large abrasion involving approximately 80% of the cornea but the results were negative for leakage. Although a posterior perforation at the location of the vortex veins was identified, it was unlikely to have been caused by the air-powered salt gun because the area was not directly exposed to the blast.
The results of this experiment show the damaging effects of the air-powered salt gun on the eye, specifically to the cornea. To our knowledge, this is the first study of its kind. One limitation was the number of globes studied. Although a Seidel-positive wound was not sustained under the conditions specified, a salt granule did penetrate full thickness through the cornea. This raises the concern of infection due to a small, non-sterile intraocular foreign body that could be easily missed on initial examination due to dissolution of the particle, especially with a Seidel-negative wound. It is possible that the lower temperature of the left eye at the time of the blast may have reduced the dissolution of the salt, or it may have altered the characteristics of the cornea to allow full-thickness perforation.
In addition to the mechanical effect of the salt, the effect of the salt granule on the chemical composition of the aqueous humor should be considered. The average salt granule weighs approximately 58.5 µg, containing approximately 0.001 mmol of sodium.1 The anterior chamber contains 200 uL of aqueous humor with 0.033 mmol of sodium.2 If a single salt granule enters the anterior chamber, it would alter the sodium concentration by 3.1%. This may lead to complications such as increased intraocular pressure and disruption of regulatory mechanisms in the anterior lens capsule, which may lead to the loss of transparency of the lens.3 The retained salt granules in the cornea would result in significant corneal edema in the region of the embedded salt particles.
Young boys are particularly at risk for injuries involving projectiles. This demographic has been shown to have a higher rate of eye injury involving BB guns.4 Marketing strategies for this product, including stickers and the toy-like design, may appeal to this demographic and place them at a higher risk for injury, especially if the product is misused or used without proper supervision.
More information is required to fully understand the impact of air-powered salt guns on the globe, such as the effects of salt particles entering the anterior chamber, how using larger salt particles will affect depth of penetration, and how the temperature of the eyes may have affected our results. Of note, the globes used in our experiment had significant corneal edema prior to use, which may have interfered with the depth of penetration of the salt particles.
Air-powered salt guns appear to be marketed toward children due to the stickers on and toy-like design of the gun. There is great concern that this vulnerable population may be at an increased risk for significant ocular damage. Our hope in publishing this report is to inform providers and notify parents of potential eye injuries related to air-powered salt guns.
- National Center for Biotechnology Information. PubChem Compound Database: Sodium Chloride. U.S. National Library of Medicine. https://pubchem.ncbi.nlm.nih.gov/compound/Sodium-chloride. Accessed September 24, 2018.
- Krupin T, Civan MM. Physiologic basis of aqueous humor formation. In: Ritch R, Shields MB, Krupin T, eds. The Glaucomas, 2nd ed. St Louis: Mosby; 1996:251–280.
- Mathias RT, Rae JL, Baldo GJ. Physiological properties of the normal lens. Physiol Rev. 1997;77(1):21–50. doi:10.1152/physrev.19220.127.116.11 [CrossRef]9016299
- Grin TR, Nelson LB, Jeffers JB. Eye injuries in childhood. Pediatrics. 1987;80(1):13–17.3601512