title: The effect of multiple antireflective coatings and center thickness on resistance of polycarbonate spectacle lenses to penetration by pointed missiles.
abstract: OBJECTIVE
  Previous work has shown that the impact resistance to blunt missiles is affected by coatings applied to either CR-39 or polycarbonate lenses. We investigated the effects of multiple antireflection (minimum angle of resolution [MAR]) coatings on the resistance of polycarbonate lenses to puncture on impact by sharp, high-speed missiles.
  
  
  METHODS
  Four groups of surfaced plano polycarbonate lenses were investigated. Two groups had a scratch-resistant (SR) coating applied to both surfaces. One of these groups had a 2-mm center thickness and the other had a 3-mm center thickness. The other two groups of 2-mm and 3-mm thick lenses had a MAR coating applied over the SR coating. The lenses were impacted by a missile consisting of an industrial sewing machine needle mounted in a cylindrical aluminum carrier.
  
  
  RESULTS
  The sharp missiles were able to pierce the lenses at speeds between 29.6 m/s and 46.2 m/s. Impact resistance was lowest for the thinner lenses and lenses with a MAR coating. The effect of the MAR and lens thickness was subadditive.
  
  
  CONCLUSIONS
  We have confirmed previous observations that polycarbonate lenses are more susceptible to penetration by sharp, high-speed missiles than blunt missiles. We have also found that reducing lens center thickness and applying a MAR coating further reduces the penetration resistance. Therefore, the use of 2-mm center thickness and MAR-coated polycarbonate lenses should be discouraged for industrial eye protectors where sharp missile hazards are possible.
authors.affiliation: School of Optometry, University of Waterloo, Waterloo, Ontario, Canada. bchou@uwaterloo.ca
authors.forename: B Ralph
authors.initials: BR
authors.lastname: Chou
authors.forename: Alina
authors.initials: A
authors.lastname: Gupta
authors.forename: Jeffery K
authors.initials: JK
authors.lastname: Hovis
mesh_terms: D020099:Coated Materials, Biocompatible; D004869:Equipment Safety; D005131:Eye Injuries / Q000517:prevention & control; D005135:Eye Protective Devices; D005139:Eyeglasses / Q000592:standards*; D006801:Humans; D008422:Materials Testing / Q000379:methods*; D011076:Polycarboxylate Cement
chemical_list: D020099:Coated Materials, Biocompatible; D011076:Polycarboxylate Cement; C005506:polycarbonate