Hayley Davidson's optician spotted the abnormality during a routine check-up at Specsavers mobile service in Thurso in September.
The 28-year-old mother only made the appointment because her daughter Rosie, 2, broke one of the legs on her glasses and she needed them repaired.
During the eye examination John Shanley noticed the life-threatening swelling on her optical nerve, which could have killed her before her wedding if left untreated.
Mr Shanley referred Hayley to her doctor and urged her to get it checked as soon as possible.
Ms Davidson said: "A couple of days later I received a phone call at work and I was referred to Raigmore Hospital in Inverness. My appointment was on 28 September and I saw a neurologist and ophthalmologist and was sent for a CT scan. The results showed I had a cyst on my brain and the doctor said I needed surgery immediately."
Ms Davidson and her fiancee, who accompanied her, were in shock and she was taken to Aberdeen that afternoon. She said: "I had to travel with paramedics in an ambulance as they were concerned that I could pass out or have a fit at any moment. I was just eager to have the surgery. With the wedding and Christmas coming up, I just wanted it done."
She had the operation to drain the cyst on October 3 and made it back home to Rosie and Murray nine days later.
"I met with my surgeon recently and he is happy with my recovery. He thinks I have had the cyst since birth but something happened at some point which caused it to swell," she said.
The cyst grew to be 7cm-wide and began to crush the left side of Hayley's brain, which reduced her peripheral vision and gave her headaches from March last year.
"I am very much a person who just gets on with their business. Nothing really drags me down but six months on, the headaches were getting worse.
"When I was bending down to pick up Rosie's toys I was getting dizzy and disorientated, so Murray said I should go and get checked out."
After visiting her doctor in August she was referred to Wick General Hospital where medical staff concluded that Hayley had migraines.
Ms Davidson paid tribute to optometrist Mr Shanley who caught the problem before its potential devastating effects.
"John is worth his weight in gold. It just shows how much more there is to an eye test than just testing your vision. It's all about the general health of the eyes and if I hadn't been to see John, I would quite certainly have gone blind and then I would have died. For me, that test was life-saving."
Mr Shanley has worked with Specsavers since 2006 and has spent the last three years with the Highlands and Islands mobile service.
"When Hayley first described her symptoms I was immediately concerned and the fact it had been an ongoing problem set off alarm bells," he said.
"I had a look in her eyes and there was swelling on her optic nerve which I found suspicious, and after further tests I immediately referred her to the hospital.
"Hayley came back in to see me the next time the mobile service was in Thurso and I was quite glad that the referral had been acted on and she received the treatment she needed to save her life."
Ms Davidson, who got married on December 28, said: "The wedding was a great day and it went by so quickly. During the ceremony the humanist celebrant mentioned what I had been through and my operation and said that if we could make it through that then we could make it through anything."