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Non-prescription sun eyewear optical performance study

1 May 2006


Non-prescription sun eyewear often has induced refractive power, prismatic deviations and variability in resolution within their lenses. The goal of current sun eyewear manufactures is to provide maximum optical quality in their lenses. In order to achieve superior optical quality in their lenses, manufactures attempt to have low refractive power, low prismatic power, and high resolution within and between their lenses. The purpose of this study was to assess various optical qualities including refractive power, prismatic deviation in primary and lateral gaze, and resolution of premium non-prescription eyewear available for over the counter purchase to consumers at local optical shops or stores. 48 pairs oflocally purchased sun eyewear from prominent national brands were purchased for this study. Two principal investigators measured both lenses in each pair of sun eyewear for refractive error and cylinder using a calibrated 8 power telescope. Prismatic deviation was measured on both lenses of each eyewear in primary gaze and 30 degrees dextroversional gaze. Resolution was also obtained for each individual lens by using the same calibrated 8 power telescope and the standard high contrast NBS Definition Pattern. All eyewear within the study produced measurable amounts of refractive power, with a majority oflenses measured producing a low minus power. Cylinder was also found in all lenses. Most lenses induced base-down and base-out prismatic deviations for primary gaze, and most lenses gave a base-out horizontal vergence effect in primary gaze. All but one lens produced base-out prism with temporal gaze and all lenses produced base-in prism in nasal gaze giving a yoked prismatic effect in lateral gazes. The majority of vertical deviations in lateral gaze were base-down. Resolution results showed large variability between lenses within the tested eyewear with over a third of the lenses not meeting current ANSI standards. It was concluded that refractive power and induced cylinder in all the lenses tested would have minimal perceptual effect based on the depth of focus innate in the human eye with variability and sensitivity most likely based on pupil size secondary to tint density. Prismatic deviations were felt to have a more detrimental effect on the viewer due to changes in perception of the viewer's environment. Resolution results were questionable based on variability in tint density and transmittance of individual lenses. Further investigation in areas of transmittance and tint are indicated in determining resolving capabilities of sun eyewear. Further testing in optical quality is also indicated and could include subjective responses to clarity and comfort in both recreational and professional athletes.


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