This is exactly why you should not buy dirt cheap knockoff erectile dysfunction drugs from spam emails.

A medical case was just published in "Retinal Cases and Brief Reports" about a 31-year-old man from New York who ordered some generic Viagra off the internet last year. He ended up taking way too much and started having a hard time seeing.

After dealing with two days of flashing light and seeing everything with a red tint, the guy went to urgent care. Doctors discovered that he had permanently damaged his retinas by taking so much of the drug.

It's a year later and and the doctors still haven't figured out a cure. They do say this is the first time taking Viagra has caused permanent eye damage. So only use it if you have a prescription and don't overdose.