Alice McCaughey, 80, was unaware that her speech was badly slurred when she went for a check up.
Staff at the branch of Specsavers, in Oak Mall, Greenock, Inverclyde, were alarmed and noticed that the OAP was struggling with her mobility.
The optician insisted Alice should go to hospital to be checked over.
A taxi rushed the gran to Inverclyde Royal Hospital, where medics quickly assessed that she was having a stroke.
Alice said: "I was going for a check up and on the way in the driver said my speech was a little odd.
"I went into the opticians and they immediately recognised it was badly slurred, even though at the time I had no idea anything was going on.
"I was completely unaware, in fact.
"The optician told me she didn't want to alarm me but said that was the second time she had noticed that with me while I was in the store.
"She said that she was sending me to the hospital to be checked over and it turned out I was having a stroke.
"I can't thank them enough for their speed of thinking.
"They possibly saved my life."
She was diagnosed with a TIA, which can lead to major stroke if it goes untreated.
Alice added: "I was in A&E then I was moved to the stroke ward.
"I can honestly say it was a privilege to be there to see for myself the amazing work the team there do.
"I just think it is important to say how great the hospital staff at Inverclyde Royal Hospital were when areas of our local services seem to keep being moved to Glasgow."
The terrifying ordeal was the second time Alice had been helped by the Oak Mall opticians, after a routine check up a few years ago identified a blood clot in her eye.
Alice was diagnosed with macular degeneration and has been undergoing a course of treatment since that sees her receive regular injections to save her sight.
She said: "They noticed I had a blood clot in my eye and sent me to hospital. I have had eye jabs since.
"I might not have realised what was happening without staff's intervention.