Triple major winner Koepka, 28, hit a poor tee shot on the sixth hole on the opening day of the Ryder Cup.
The ball went into the crowd and hit Corine Remande, 49, in the eye and left her needing medical attention.
Blood was gushing down her face and she has now said scans have revealed her eyeball exploded and her socket was fractured, causing her to lose sight in that eye.
And she says she will now sue the organisers for failing to keep her safe.
“Quite clearly, there is responsibility on the part of the organisers,” Ms Remande said as she left the Croix-Rousse hospital in Lyon where she had been transferred to from a Paris hospital.
“Officials did not shout any warning as the player’s ball went into the crowd.”
Koepka tried to comfort Ms Remande and afterwards said he felt terrible about the incident.
“I tried to stay positive with him so that he didn’t lose his concentration,” she said.
Brooks Koepka struck a spectator in the face during the Ryder Cup
Brooks Koepka checks on the spectator after hitting her in the eye
Brooks Koepka’s ball hit the spectator and has damaged her eye socket
“But once I was taken away, I didn’t hear anything from the organisers.
“More than anything I want them to take care of all the medical bills to make sure there is no risk of infection.
“However they told me I’d lost the sight in my right eye, and this was what was confirmed to me today (Monday).”
Her husband said: “In the best case scenario, she may be able to see shapes after the bruising eases in a month or so.”
Koepka, who won two of his majors this year, is ranked third on the PGA Tour but was unable to stop America losing the Ryder Cup to Europe at Le Golf National in Paris.
Koepka won 1.5 points from his four matches as American went down 17.5-10.5 and extended their poor run on European soil.
Brooks Koepka hit a stray tee shot on the sixth hole at Le Golf National
During the match the TV commentators noticed Koepka looked ‘shaken up’ after the incident.
“I hate to report this but Brooks is a little shaken up,” one of Sky Sports’ on-course commentators said.
“A spectator caught the golf ball. It looks to be right above her eye.
“There are fairly worrying moments for one of the fans out here. Hopefully everything is okay.”
And he was asked about it at the end of his round.
“I haven’t gotten an update,” Koepka said after completing his first round on the Friday when asked about the spectator’s condition.
“I actually just asked in the locker room, and nobody knew. So I have no idea what’s going on.
“I obviously saw her. It looked like it hurt. She was bleeding pretty good. It looked like it hit her right in the eye, so hopefully there’s no, you know, loss of vision or anything like that.
“But it’s not a fun feeling. I probably do it way more than I should. It seems just about every week we’re hitting somebody, and you know, it’s unfortunate. You’re never trying to.
“It doesn’t feel good, it really doesn’t. You feel terrible for them.
“You know exactly how they are feeling, especially when you’ve got to go over there and apologise, because they are in pain, usually bleeding, and then to hit her in the face is not — you don’t want to hit anybody in the face, especially not a woman, and it’s not a good feeling.
“I mean, I had a terrible — I just wanted to get out of there, so I’m glad Tony was able to chip-in and leave.
“But I’m sure we’ll get an update on her in the next — whenever we leave here, but hopefully she’s doing good.”
Brooks Koepka was on the losing side at this year’s Ryder Cup
Europe captain Thomas Bjorn added: “”For me, the whole team I represent and everybody at Ryder Cup Europe, it’s just a terrible thing and something that you don’t want to happen.
“It’s terrible, it’s a freak accident that’s happened, and all our thoughts are with her.”
In a statement a Ryder Cup spokesperson said: “It is distressing to hear that someone might suffer long-term consequences from a ball strike.”
BBC Sport’s golf correspondent Iain Carter said: “Spectating at golf tournaments can be a hazardous business. Top players are not as precise as you might expect and errant tee shots occasionally have nowhere to go other than into packed galleries.
“These misdirected missiles have the speed to do plenty of damage but more often than not injuries are limited to cuts and bruises. Players usually offer a signed glove to the victim, as if that will ease the pain.
“In more serious incidents, injuries can be very unsettling for the players involved. The majority sound a warning cry of “fore” but there are some who appear content to allow fans to be a barrier to prevent their balls from flying into deeper trouble and remain silent in the wake of wayward blows.”