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Eyes are amazing! Think about it: People with sight rely on two balls of clear jelly to focus light on some special cells and create the whole experience of vision.

And for two balls of jelly, eyes are surprisingly robust—you get one set of them, and they generally last your whole life. But sometimes, they don't work perfectly, so these days, many people turn to laser eye surgery—like Lasik and cataract removal—to repair their vision. I mean, I've done it!

And if it's ever struck you as bizarre that millions of people have signed up to have a surgeon shoot lasers into their eyeballs—well, yes. But, it's all thanks to the history behind these procedures that they're as successful and common as they are today. When eyes fail, it's often because something about the shape of the eye is preventing light from focusing perfectly.

Like, if your eye is too long or too short, or if the curve of the cornea—that clear part at the front of your eye—isn't just right, light can get focused onto the wrong spot. That makes people nearsighted or farsighted—or causes astigmatism. These are often problems glasses can fix—but eventually, doctors began looking for more permanent solutions.

And that's how lasers entered the game. Back in the 1970s and '80s, lasers were improving dramatically and transforming all sorts of science. One of the really big inventions of the time was something called the excimer laser, a really precise type of laser that was originally used for physics and chemistry research.

But eventually, ophthalmologists realized that maybe they could use this laser, too… to perfect people's vision. At the time, many of them were using a technique called radial keratotomy to surgically improve the vision of nearsighted people. The modern form of this surgery had been refined and made popular by the Soviet ophthalmologist.

Svyatoslav Fyodorov, who would cut slices in the cornea that looked like the spokes of a wheel. This flattened the cornea, which moved back the focal point of light and corrected nearsightedness. And for many patients, that worked pretty well!

But there were also some issues. Like, often, the cornea would keep getting flatter over time, so people who started out nearsighted would end up farsighted after a few years… and then need glasses again. Plus, using a blade on such delicate tissue was risky and depended heavily on the skill of the surgeon.

But excimer lasers are extremely precise and controllable. So, the idea behind the surgery was this: You'd first carefully cut a flap in the top layer of the cornea, then lift it back, revealing the inner part. Next, using the laser, you'd vaporize parts of the cornea to achieve the desired shape.

Once that was done, you'd just put the flap of cornea back on top, let it heal, and end up with a new and improved eye. Today, that's known as Lasik eye surgery, a process that hundreds of thousands of people still get every year! Compared to older methods, the laser was easier to standardize, and the results were much more stable, so it became the procedure of choice for ophthalmologists everywhere.

But this wasn't the end-all solution for blurry vision—especially because, no matter how well you can shape the cornea, that doesn't help if the lens beneath it is cloudy. As we age, proteins in the lens of our eyes naturally start to clump up and create cataracts, which cloud the lens. They're entirely normal, but they can make it hard to see and cause blindness if they go untreated.

Scientists did have a way of breaking up cataracts at the time—they'd use a tiny needle with a vibrating tip to break up the lens before sucking it out of the eye. But unfortunately, the constant, rapid in-and-out motion built up heat quickly, and sometimes it burned the cornea. So surgeons had to—and still have to—be very careful with this method.

Then, around the same time that people began putting their eyes under the laser for Lasik-type surgeries, the ophthalmologist and inventor Patricia Bath wondered if excimer lasers could also be applied to cataracts. The light from these lasers is so high-energy that it vaporizes tissue without heating it up, and Bath thought it could potentially break up cataracts without the risk of burning surrounding tissues. Over five years, she developed a device called the Laserphaco Probe, which became an extremely safe and effective tool for breaking up cataracts in the lens.

The method involves pushing a small needle embedded with a fiber-optic cable and a tiny vacuum through the side of the eye. Then, surgeons shoot an excimer laser through the cable directly onto the lens to break it up, before sucking it out with the vacuum. Finally, they insert a new, artificial lens made of durable, clear plastic.

When Bath patented the probe in 1988, she became the first Black woman to hold a patent for a medical device. Her invention significantly lowered the risk of complications, and it was adopted around the world. Since then, technology has continued to advance.

Some surgeons have refined an older practice of using ultrasound to break up cataracts, while others have begun using the smaller femtosecond laser in place of the excimer laser. Still, the general concept—of using a laser to break up cataracts—remains one of the most widely-used technologies for extracting cataracts around the world. Since their invention, lasers have remained a major player in medicine as scientists try to keep up with the challenge of keeping our eyes clear, healthy, and focusing.

And with hordes of people putting their eyes under surgeons' lasers every year, laser eye procedures are some of the most common and successful surgeries in the modern world. Thanks for watching this episode of SciShow! If you liked it, and if you're curious about what exactly surgeons are shooting lasers into, you might enjoy our episode about what eyes are made of.

You can watch that right after this! [♪ OUTRO].