It’s really easy to find eyeglass stores that also offer eye exams. You get your eyes checked, pick out the frames, and get the final product all from the same place, so you might not notice that you didn’t get a copy of your prescription after the exam. That’s against the law, and one federal agency is reminding eye doctors of the costly penalty for failing to provide prescriptions.

The Federal Trade Commission’s Eyeglass Rule requires that patients receive a copy of their new prescription after an exam — even if the patient doesn’t request it. Nor can the eye doctor charge a fee for releasing the prescription.

Eye doctors are also barred from offering exams only to people who buy glasses from them, so if you go to an eyeglass store and just want the eye exam, they can’t turn you away.

Finally, the prescription can’t include any sort of language that the eye exam is only accurate for the glasses sold by the eye doctor’s store.

Violations of the Eyeglass Rule can result in fines of $16,000 per violation, which is why the FTC recently sent warning letters to 38 eyeglass prescribers [sample PDF] with warnings that the Commission had received complaints about patients failing to receive copies of their prescriptions.

The letter advises these prescribers to review the Eyeglass Rule to make sure their practices are in compliance before the FTC brings down the financial penalty hammer.

The Eyeglass Rule is very similar to the FTC’s Contact Lens Rule, which also requires that patients receive copies of their prescription.

Things have gotten particularly troubling in the contact lens world in recent years, after lens makers decided to establish price floors that favored eye doctors, meaning that no retailer can sell contact lenses for less than the price established by the manufacturer. That benefits eye doctors because consumers have no incentive to do comparison shopping, as the lenses will be same price no matter where they go; might as well buy from the person doing the eye exam, right?

Utah lawmakers passed a law banning this price-fixing, and has been fighting the lens manufacturers in court over the legality of the statute.

The folks at 1-800-CONTACTS, who have a vested interest in this issue, recently alerted the FTC to several thousand allegations of eye doctors failing to turn over contact lens prescriptions as required.

For more on your rights under the Eyeglass and Contact Lens Rules, check out this page on FTC.gov.