On a recent afternoon in Paris, a woman was having her eye color changed from brown to green.

She was lying supine on the operating table, her left eye clamped open with an ophthalmic speculum while a doctor used a scalpel to slowly inject the pistachio green, mineral-based pigment into her cornea.

Observing the surgery was Dr. Francis Ferrari, the French ophthalmologist at the New Eyes Paris clinic who invented the cosmetic process, called Femtosecond Laser-Assisted Annular Keratopigmentation, or FLAAK, just over a decade ago.

He rolled his stool closer to the monitor, which projected an extreme close-up image of the eye. “Not too much in the left eye,” he told his colleague Dr. Jean-François Faure, who murmured in agreement, his own eyes focusing through the surgical microscope as he worked.

Just hours earlier, Ferrari consulted with the patient, holding up a plastic model of an eyeball. “The color of the eye is determined by the iris, and we won’t be changing the color of the iris,” he said. “We will be hiding the color of the iris by coloring the space in front of the cornea, similar to a contact lens, and with a laser, we will create a circular incision through which we will inject the color. Do you understand?”

“Oui, docteur,” said Ayşegül Kolvert, 35, who had traveled to Paris the previous day from Grenoble in southeastern France with her twin brother, Karl, who came to support her. She’d always dreamed of having green eyes. And, she said, “I was tired of wearing contact lenses.”

Kolvert is one of more than 2,500 people who have come to New Eyes Paris, located on a quiet street in the well-heeled Sixth Arrondissement, seeking the surgery. Many of Ferrari’s patients learned about keratopigmentation through social media, and often message the doctor directly on Instagram to book initial appointments over Zoom calls. Most want to transition from dark to light shades, choosing among a range of pigments that include olive green, pistachio, “Riviera blue,” “honey gold” and “ocean.”

The procedure is performed every Wednesday in a clinic that was formerly a stained-glass factory, which is rather fitting for an establishment where two doctors, who in some sense regard themselves as artists, stain the proverbial windows of the soul. Within a few hours, the patients leave with the eyes of their dreams. Recovery lasts a single day.

Ferrari and Kolvert studied the simulation on a laptop to see how the pistachio green would look in her eyes. “Are you sure it will look green enough?” Kolvert asked. Ferrari assured her it would.

There are three levels of color density: weak, medium and strong. “Weak is very natural, but not very visible,” Ferrari said, “so many of our patients who want a medium density, knowing that it will fade, will get strong, which looks unnatural at first.”

Because a cornea never completely heals, a patient who is not pleased with the results of the keratopigmentation can remove about 80 percent of the color — though it’s not advisable.

Within the wider ophthalmology community, the procedure is highly controversial since manipulating the cornea comes with a host of potential complications. Cosmetic keratopigmentation is not approved by the Food and Drug Administration, and the American Academy of Ophthalmology has issued two warnings against getting the procedure, citing dangers including corneal scarring, infections and serious vision problems including the risk of blindness.

“I think there’s a lot of fear among ophthalmologists, especially because there’s not really any long-term data on the procedure itself and the pigments that are used,” said Dr. Amita Vadada, an ophthalmologist and a clinical spokesperson for the A.A.O. “The eye is a very sensitive organ, immunologically,” she said. Vadada is especially concerned with foreign pigments being injected into the corneal layers, which can cause inflammation. “Unlike other parts of the body, even low-grade inflammation of the eye can lead to permanent scarring, light sensitivity and pain,” she said, adding that with keratopigmentation, “you’re potentially altering the function of the eye.”

Ferrari insists that FLAAK is no more dangerous than LASIK surgery, and carries even fewer risks than wearing contact lenses, which are prone to infection and corneal ulcers. He claims the process is safer than both laser depigmentation and iris implant surgery. The latter surgery is an alternative color-changing technique often known by its brand name, BrightOcular. It is another controversial procedure in which colored silicone is inserted into the eye. It is now at the center of several lawsuits.

Above all, Ferrari views his procedure, FLAAK, as a way for patients to become who they’ve always wanted to be.

“There’s real suffering,” he said. “Of course, it would be better to accept one’s natural eyes, but there are some patients who aren’t able to.”

The Eyes and the Hands

At 67, Ferrari is tall and soft-spoken with, perhaps fittingly, watery, greenish-blue eyes that rarely seem to blink, especially while engaged in conversation. He was raised in Luxembourg by a father who worked as an interpreter, from French to Italian, for the European Parliament, and a mother who was a homemaker. Trained in ophthalmology at Eberhard Karls University of Tübingen in Germany, he is the first person in his family to pursue medicine and may well be the last, as all four of his sons have chosen careers in business or theater. Ferrari prides himself on being able to conduct his consultations in English, German and Italian, in addition to French.

Ferrari has worked with his colleague Dr. Jean-François Faure, 70 — who also has greenish-blue eyes — since 2019, when Ferrari decided to open his keratopigmentation practice in Paris. Ferrari was looking for a pre-existing clinic that was both aesthetically beautiful and practical, with all the necessary equipment already available. And so he approached Faure, who was already running a clinic that offered regular ophthalmological services like eye exams, cataract surgery and some laser surgery. Ferrari works only on Wednesdays. He is otherwise back at home in Strasbourg with his wife (who has brown eyes).

Ferrari does the consultations and oversees the FLAAK procedure in the operating room. But he hasn’t performed the surgery in two years, though he declined to say why. Faure, a seasoned surgeon who happens to be ambidextrous, does the procedure.

The two make quite the pair. Ferrari serves as the eyes; Faure, the hands.

The idea for keratopigmentation came to Ferrari 15 years ago, when he was reading an online discussion among French ophthalmologists about the best way to color eyes. Keratopigmentation was originally developed as a way to treat conditions like aniridia, in which an eye is lacking all or part of an iris and therefore becomes extra sensitive to light.

“I thought to myself that it would be good to find a technique that permits you to change the color of your eyes in a safe way, and then I thought,” Ferrari said, widening his own eyes as if reliving the memory, “the cornea.” That was in December 2011.

He began to experiment on rabbits. “If you write this in your piece, I’ll get all the animal lovers after me,” Ferrari said. He reached for his phone to pull up a series of images of a white rabbit with red eyes, anyway. The red eyes were successfully changed to blue using the FLAAK method. Ferrari would later remove the eyeballs to dissect and study them under a microscope. He tried the technique on other rabbits, too. “And I gave them my sons’ names,” he said sheepishly. Ferrari first tried the procedure on a human in December 2013 — the world’s first.

He was motivated to work quickly, worried someone would beat him to it. And he wasn’t wrong to think so: Another ophthalmologist, Dr. Jorge Alió, who is based in Alicante, Spain, was simultaneously thinking about it, too.

“I’d been researching keratopigmentation for therapeutic purposes,” Alió said. He had been looking for ways to address ocular trauma. “I had no solution other than a prosthesis or a contact lens, which often cannot be used in this space because they are destabilized.” Alió’s clinic received a grant from the Spanish government to develop pigments.

“We developed this whole new technique,” he said. “It was very experimental.” And, as it turned out, very inspiring; it gave him the idea that the surgery could be used for cosmetic purposes.

After learning of each other, Ferrari and Alió met in person at a conference in London. The meeting was very cordial, and though Alió likes to point out that he has written more academic papers and pioneered the technique for therapeutic as well as cosmetic use, the two doctors, perhaps unusually, have agreed to be named as “co-inventors.”

How to Make Their Brown Eyes Blue (or Green)

The operation is not for the squeamish. After the eyeballs are numbed, the femtosecond laser is beamed into each eye, cutting a circular tunnel within the cornea. After using an ordinary surgical hook to widen the incision, Faure carefully slides the full arch of the “Ferrari scalpel” into each cornea — which have a jellylike consistency — and, with a series of decisive strokes, nudges the pigment onto them. The dye slowly swirls in, like an ink droplet in water.

The strange thing, to the observer, is how the eye ceases to resemble one the more you stare at it. It could be an abstract painting, or a planet viewed through a telescope. The final result is like an eclipse: You can see the loop of Riviera blue or pistachio, and, beneath it, the specter of the old iris.

Though the doctors are working to improve their current technique to add freckles, radial furrows and color variation to make eyes appear more natural, subtlety or realism aren’t always the ambition. Often the “fakeness” of it is the attraction.

The eye doctor’s job is to appease. “There’s a lot of conversation involved, lots of dialogue with the patient,” Faure said.

“People always want more,” Ferrari said. “You know, there’s a saying: More is the enemy of good.”

The surgery at Ferrari’s clinic costs 7,000 euros ($8,100). Clients must pay a €1,500 deposit, which is refundable, said Ferrari, “if, during the consultation, I noticed something in their eye that means the procedure cannot be done.”

Each client has a 20-minute consultation the morning before the procedure — often the first and only in-person consultation. With a speculum microscope, Ferrari uses Optical Coherence Tomography to study the prism on the back surface of the cornea, and makes an image of the retina to ensure the patient’s eyes are healthy enough to undergo the treatment. Then Ferrari and the patient finalize the eye color, toggling among different simulations on a laptop.

One of Ferrari’s former patients, Viviane Pouget, 69, had never considered changing her brown eye color until she’d watched a television segment about the procedure on a Friday six years ago. She called his clinic, which was then based in Strasbourg, the following Monday.

“I thought to myself, Why not?” The next week, she saw Ferrari. “Of course, like anyone would be, I was nervous,” Pouget said. “What would happen? What was I signing up for?”

She was stunned by the transformation to Riviera blue. “They were brighter than I could have hoped,” she said. “I looked at myself in the mirror and said to myself: I love myself, I appreciate myself.”

Pouget said she noticed her life change instantly. “After leaving the clinic, I took the train back to Paris and someone helped me with my suitcase. In my entire life, no one ever carried my suitcase before,” she said. “I think when people see blue eyes, they think of the sea. When we see dark eyes, we see more authority.”

The Competition

There is now a growing web of doctors performing keratopigmentation around the world, including Dr. Alexander Movshovich, in New York and Miami, and Dr. Brian Boxer Wachler in Los Angeles, both of whom were trained by Ferrari. In Paris alone, there are six competing clinics offering the procedure, which is why New Eyes Paris offers FLAAK only on Wednesdays. With all the competition, filling the clinic each week would be difficult.

Ferrari believes copycats are an inevitability and acknowledges that there’s something flattering about them. “There’s money to be made,” he said. “It’s new. It makes a change from the ordinary routine.” But there’s little Ferrari can do to mitigate the uncredited use of his process. In medicine, while you can occasionally patent the technology, it is nearly impossible to patent a procedure. Even the scalpel, which he designed and patented, has been copied elsewhere, he said.

He has been offering an in-person, daylong course at the clinic to train ophthalmologists as a way to further monetize keratopigmentation. Recently, a doctor traveled from India to learn from Ferrari.

And he has managed to get some recognition. On the desk he shares with Faure sits an octagonal glass trophy, which was presented to him by Alió, recognizing Ferrari as “Best Speaker” at the second annual Kolor Congress in Dubai last year, a conference for ophthalmologists already practicing keratopigmentation and others looking to do so. This year’s two-day Kolor Congress, which took place in May at the Radisson Blu hotel in Nice, drew a 300-strong, international crowd of ophthalmologists. There, they witnessed live demonstrations using the latest techniques and pored over swatches for new pigment shades.

“They Are Green?”

On that particular Wednesday afternoon, there were four patients. Kolvert was the first. She had been excited in the lead-up, but as with many entering the operating room and seeing the two doctors masked up to the eyes, her hands began to tremble. A junior optometrist assisting with the operation handed her a couple of stress balls to squeeze.

Some patients get cold feet and cancel at the 11th hour. It doesn’t necessarily surprise Ferrari.

Throughout the operation, Faure talks to the patient, describing what he is doing. He periodically asks them to “look down” at their feet, or to keep their focus on the ceiling as he targets the full periphery of the cornea.

After 45 minutes, Faure put down his scalpel. “C’est fini,” he said. The surgical drape was gently lifted from Kolvert’s face, and the speculum unlatched.

“All OK, doctor?” she asked, gingerly sitting up. An artificial teardrop slid down her cheek. “They are green?”

“They’re green, they’re green, they’re green!” Ferrari merrily exclaimed, approaching the patient to admire his colleague’s handiwork, and the fruits of his invention.

“I just really want them to be green,” said Kolvert.

“No more,” Ferrari cautioned Faure.

There was a brief silence as Kolvert studied her eyes in the New Eyes Paris-branded hand mirror.

“C’est magnifique,” she said. Then she paused, glanced at the doctors and then back at herself, and tentatively said, “But doctor, they aren’t green enough.”

“I can promise you, they’re green,” Ferrari told her.

As she beheld the sight of her new eyes for the first time, Kolvert was bursting with joy and disbelief. After checking to make sure that they were as green as they could go, she thanked the doctors and giddily walked out of the operating room, past the antechamber where the next patient was being readied for surgery, to where her brother was waiting.

“That’s you,” said her twin, rising from his chair. He hugged her, then took a couple of steps back to have a proper look. “Those are your eyes.”