Effect of multiple antireflection coatings on impact resistance of Hoya Phoenix spectacle lenses.
OBJECTIVE
To investigate how the impact resistance of Hoya Phoenix spectacle lenses is affected by centre thickness and the application of a multilayer antireflection (MAR) coating.


METHODS
Four groups of plano lenses were tested: dress thickness with scratch resistant (SR) coating on both surfaces, dress thickness with SR and MAR, industrial thickness with SR and industrial thickness with SR and MAR. Lenses were edged to a clear circular aperture of 50 mm with a 0.5 mm hidden bevel and mounted in a specially-designed lens support. A pneumatic gun was used to propel a 6.35 mm steel ball at the centre of each lens. Impact speed was varied using the ZEST protocol to determine the threshold breakage speed.


RESULTS
The threshold breakage speeds of the dress and industrial thickness SR lenses were 55.1 and 63.2 m/s, respectively and the corresponding threshold breakage speeds for SR-MAR lenses were 50.1 and 54.7 m/s. All comparisons were statistically significant using Student's t-test with a rejection level of p < 0.005. Unlike polycarbonate lenses, dress thickness Phoenix lenses do not display 'oilcanning' deformation on high energy impact and therefore are less likely to be dislodged from their mountings.


CONCLUSIONS
We found that the mean impact resistance of the Phoenix lenses was greater than the level required of eye protector lenses by the standards AS/NZS 1337:1992, ANSI Z87.1-2003 and CSA Z94.3-02. Similar to CR39 and polycarbonate, the application of MAR to Phoenix lenses reduces their impact resistance, however, they provide an acceptable level of impact protection in industrial settings, where there is little danger of exposure to pointed or sharp-edged high-speed missiles.
School of Optometry, University of Waterloo, Waterloo, Ontario, Canada. bchou@uwaterloo.ca
B Ralph
BR
Chou
Jeffery K
JK
Hovis
D020099:Coated Materials, Biocompatible; D005139:Eyeglasses / Q000592:standards*; D006801:Humans; D066298:In Vitro Techniques; D008422:Materials Testing; D011108:Polymers; D013499:Surface Properties
D020099:Coated Materials, Biocompatible; D011108:Polymers