title: Impact resistance of common spectacle and safety lenses to airgun and rimfire projectiles.
abstract: OBJECTIVE
  To evaluate the penetration resistance of common spectacle and safety lenses to high-velocity projectiles and to examine the current recommendations regarding the use of such lenses.
  
  
  METHODS
  The penetration threshold of glass, high-index, and polycarbonate spectacle and safety lenses was determined by firing BBs, pellets, and 0.22-caliber projectiles. The mass, diameter, velocity, and energy of each projectile were measured, and the center thickness, mass, and refractive power of each lens were recorded. The penetration threshold for each lens type was calculated, and a comparison of impact resistance was made.
  
  
  RESULTS
  The maximum velocity of the BB was measured at 221 m/s; pellets at 210 m/s; CB.22 rimfire projectiles at 204 m/s; and 0.22 rimfire projectiles at 290 m/s. The BB penetration thresholds were as follows: glass lenses = 84.0 m/s (2.4 J) and high-index lenses = 107.7 m/s (4.09 J). Polycarbonate spectacle and safety lenses were not penetrated by BBs regardless of their velocity; however, these lenses were penetrated by CB.22 rimfire projectiles (89.2 J). Review of the penetrated lenses showed that center thickness and refractive power was comparable between the various groups of projectiles.
  
  
  CONCLUSIONS
  Polycarbonate offers a vastly superior degree of penetration resistance compared with other commonly used lens materials. The current recommendations regarding the use of polycarbonate in prescription and protective lenses, as endorsed by the American Academy of Ophthalmology and the American Academy of Pediatrics, must be reevaluated.
authors.affiliation: Department of Ophthalmology and Visual Sciences, University of Louisville School of Medicine, Kentucky 40202, USA.
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Rychwalski
authors.forename: Eric A
authors.initials: EA
authors.lastname: Packwood
authors.forename: Oscar A
authors.initials: OA
authors.lastname: Cruz
authors.forename: John B
authors.initials: JB
authors.lastname: Holds
mesh_terms: D004869:Equipment Safety; D005131:Eye Injuries / Q000209:etiology / Q000517:prevention & control; D005135:Eye Protective Devices / Q000592:standards*; D005139:Eyeglasses / Q000592:standards*; D005389:Firearms; D005898:Glass / Q000592:standards*; D006801:Humans; D008422:Materials Testing / Q000379:methods; D011076:Polycarboxylate Cement / Q000592:standards*; D014948:Wounds, Gunshot
chemical_list: D011076:Polycarboxylate Cement; C005506:polycarbonate