A Houston man filed a lawsuit this week in federal court against Pfizer, claiming he suffered Blindness after taking its best-selling impotence drug Viagra.

James Thompson filed the civil suit against Pfizer in the U.S. District Court for the Southern District of Texas on Tuesday and is seeking more than $75,000 for his vision loss.

He is also seeking class-action status because it has been estimated that 23 million people have taken Viagra, the trade name for the drug sildenafil, since 1998.

The U.S. Food and Drug Administration said last month it had received more than 40 reports of blindness in men taking impotence drugs, but had not determined if the drugs were responsible.

In the court filing, Thompson says the company failed to warn consumers that taking Viagra could cause non-arteritic anterior ischemic optic neuropathy (NAION), which restricts the flow of oxygenated blood to the optic nerve, causing irreversible vision loss.

“We believe (the lawsuit) has absolutely no merit nor is it appropriate for class-action status,” Pfizer spokesman Bryant Haskins said.

Pfizer said last month a review of 103 Viagra clinical trials involving 13,000 patients found no reports of NAION.

A lawyer for Thompson said a key issue in the case would be proving that the same underlying conditions that can be responsible for Erectile dysfunction did not cause the vision problems.

Pfizer has said NAION is the most common acute optic nerve disease in adults over age 50 and it shares a number of common risk factors with Erectile dysfunction, including high blood pressure, High Cholesterol and Diabetes.

The first pretrial hearing in the case is scheduled for November 4th.