Prescription glasses purchased online often substandard
MedWire News: Many prescription glasses obtained from internet-based sources fail to meet US optical tolerance and impact resistance requirements for eyewear, researchers report.
"Many patients likely do not realize that - and many online vendors in this study did not act as though - spectacle lenses that provide refractive correction are classified in the United States by the US Food and Drug Administration as Class I Medical Devices," say Karl Citek (Pacific University College of Optometry, Forest Grove, Oregon, USA) and co-investigators.
Writing in the journal Optometry, they add that to guarantee the efficacy of any pair of prescription glasses "a valid prescription from a licensed doctor is required, optical tolerances should be maintained, and physical requirements, including impact resistance, must be met."
The assessment of 308 lenses of 154 pairs of glasses ordered from 10 of the most frequently visited online glasses vendors revealed minor and major errors in the properties of the glasses provided.
For example, single-vision lenses with total power for near vision were received for three orders of bifocal spectacles. Twenty-five pairs of glasses had antireflective coating or photochromic lens treatments incorrectly added or omitted.
Citek and team found that 44 pairs (28.6%) of glasses received had one or more lenses that failed at least one measure of optical analysis testing and 22.7% of glasses had at least one lens that failed impact testing - based on center thickness and lens treatment. In all, 44.8% of glasses failed at least one measure of optical or impact testing.
Optical parameters measured included: sphere power, cylinder power and axis, add power, and horizontal prism imbalance.
The team found that failure to meet the outlined optical parameters were due to events such as an absence of adequate sphere power tolerance in eight pairs of glasses, an absence of cylinder power tolerance in four pairs, and an absence of adequate cylinder axis tolerance in eight pairs of glasses.
In addition, 12 bifocal lenses and 27 progressive addition lenses had incorrect add power, and seven lenses had horizontal prism imbalance.
"However, because we received no more than 20 pairs of spectacles from any single vendor, we cannot make any meaningful comparisons between vendors or draw any conclusion about the performance of any individual vendor," remark the researchers.
Citek and team therefore conclude that although it appears that buying eyewear online carries a marked risk for inaccuracy, further study is required to validate the findings.
By Lauretta Ihonor