Dr. Benoit Frenette an associate professor at the School of Optometry of the Université de Montréal recently published a study done on ordering glasses online and found a staggering 94% were made incorrectly.
"Products were evaluated using parameters standardized by the American National Standards Institute (ANSI) and the International Organization for Standardization (ISO). In terms of adhering to the prescription, regarding the desired adjustments for minimal wearing comfort, and considering the PD measurement taken by the subjects themselves, we
arrive at a 94% failure rate."
The full article can be found in the Canadian Journal of Optometry Vol. 74 No. 2 2012 on pages 16-17: http://opto.ca/media/news-publications/cjo/pdfs-docs/CJOVol74No2.2012.pdf