Optometrists cannot legally share a patient's pupillary distance measurement

In most US states, optometrists measure pupillary distance (PD) during every eye exam but are not required — and in some cases are actively discouraged by their employer — to include it on the prescription, because PD is the one measurement patients need to buy glasses online instead of at the in-office optical shop. Without PD, a patient cannot order from Zenni, Warby Parker, or any online retailer, effectively trapping them into buying from the optometrist's dispensary at 3-5x the online price. The FTC's Eyeglass Rule requires release of the prescription but does not explicitly mandate PD inclusion, and state optometry boards — staffed by practicing optometrists who profit from dispensary sales — have no incentive to close this loophole. Patients can measure PD themselves using ruler-and-mirror methods, but the results are unreliable enough that many give up and buy in-office.