Shares in Staar Surgical Co. lost nearly 4 percent after it said U.S. regulators told the company its clinical study procedures for its vision-improving implants are not in compliance with federal rules.

The Food and Drug Administration sent a warning letter outlining four compliance failures and asked the Monrovia-based biotech company to outline how it plans to fix the issues, Staar said in a regulatory filing.

The violations are related to procedures for conducting trials of the company’s implantable contact lenses and the process for applying for FDA marketing clearance. The FDA letter said Staar didn’t “immediately conduct an evaluation of all unexpected adverse device effects.”

The filing said that the FDA found instances between 2002 and 2005 of the company’s not meeting these regulations, ruling that Staar’s responses to the incidents in a letter sent April 5 were inadequate.

Staar said it will respond in writing no later than the July 18, the deadline set by the FDA.

Shares in Staar dropped 14 cents, or 3.5 percent, to $3.91 in afternoon trading on the Nasdaq.