Like most scientific advancements, collaboration is the key word. If you asked who invented the light bulb, you might get the name Thomas Edison. But science and technology no longer work that way. Thousands of people from all walks of life have contributed to the invention process. The ultimate point of science and technology is to make it work for humans, and laser vision correction is such an example.

Sculpting the cornea with the Alcon Wavelight EX-500

The Alcon Wavelight EX-500 Excimer Laser

The excimer laser that does the actual sculpting of the cornea comes from semiconductor manufacturing technology. Making computer chips requires very fine sculpting of silicon. When this same ultraviolet laser light is applied to biologic tissue, it can sculpt without any collateral damage. Most lasers burn, or heat, or scar, or coagulate. But the excimer vibrates the bonds between molecules and lifts them off, like vaporizing the top layer of molecules. After lifting off this layer, what’s left behind is all normal tissue. No scar, no burn, no tissue shrinkage.

If a pulse of the excimer laser can lift off a spot of cornea, and the spots can be placed precisely, you can see how a pattern of many spots–some left, some right, some up, some down, some doubled up–can lift off a shape. Essentially, the shape that is sculpted is the shape of the would-be contact lens that would re-focus the eye. LASIK is basically sculpting the shape of a contact lens onto your cornea! The most precise excimer laser is the Alcon Wavelight EX-500, and that’s what you’ll find at Wills Laser Vision at Princeton.

Called the “halo”, the horse-shoe shaped device hovers over the eye and houses three infra-red sensors. Like GPS, it tracks the pupil of the eye and centers the excimer laser axis to the optical axis of the eye 500 times a second, to insure superb accuracy of placement of laser spots to the cornea. 

To make sure each pulse of the laser is placed at the proper spot on your cornea, the laser must be absolutely aligned with your eye. The EX-500 does this by using the most precise pupil tracking system. It employs an infra-red laser system to find your pupil, the black hole in your iris through which you see. This technology comes from NASA. In the same way a spaceship can find a circular door to which to dock while traveling at great speeds in outer space, the EX-500 laser can find and track your pupil. This tracking system then aligns the axis of the treating laser to the center of your pupil 500 times a second. That’s faster than the pulsing of the laser and faster than your eye can move.

So, the sculpting laser is absolutely locked onto your eye during the treatment. Yes, you are asked to look at a green blinking light during this quick process but feel confident that any and all eye movements are compensated for.

Further, there’s a safeguard cut-off. If your eye moves greater than 1 mm, the tracker will turn the laser off. So even if you coughed or hiccuped during the brief treatment, nothing bad happens. It just shuts off. The doctor will ask you to re-focus on the green blinking light, step on the pedal, and the laser spot pattern will resume where it left off.

Of course, you want to apply this sculpting laser to the inert part of the cornea. That’s the stroma, or middle layer. The stroma is like clear cartilage. If you sculpt it, it stays that shape.

LASIK treatment with the Wavelight EX-500 laser

Creating the flap with the Alcon Wavelight FS200

However, the stroma is covered by skin. If you sculpted skin, it would grow back, and so it would do no good to sculpt at that layer. To gain access to the inert stromal layer, in Lasik, you must create a flap. The flap is like creating a blister and flopping it over, out of the way, to expose the stroma. Amazingly, after the laser, the flap is replaced and re-adheres in a matter of minutes and is solidly adherent in a week.

The Alcon WaveLight Femtosecond 200 Laser

To create a flap, another laser, called a femto-second laser, is used. This is borrowed from the material processing and semiconductor industry. This laser is pulsed in a femto-second, which is 1/1,000,000,000,000,000 of a second. Imagine, light can go around the world 7 times in one second. In one femto-second, light travels less than a micron, which is one millionth of one meter. When a laser is pulsed that fast, it disrupts atoms. It separates the electrons from the nuclei. A vacuum is created. Nature abhors a vacuum. When it collapses, vibrations are created. These create a micro-disruption, which creates a bubble inside a cornea.

The Alcon Wavelight FS200 FemtoSecond laser harnesses this technology to create a perfect flap. It creates a wall of bubbles at a certain distance set by the surgeon below the surface of the cornea. In fact, 1.3 million micron sized bubbles are placed side-to-side to create the bottom of the flap. More are stacked to create the edge of the flap, saving a connection called the hinge. This is painless and takes 6.5 seconds.

Coupling the eye with the laser for LASIK surgery
The eye is firmly coupled with the laser in two steps. First step involves applying the purple ring on the eye with suction, using a force no more than a hand shake. The second step involves the lowering of the cone shaped into the suction ring, which is coupled with suction as well.

How does the guide the location of the bubbles? Another great technology. A suction ring must be placed on your eye. The force of the suction is no more than the force of a handshake. It’s awkward, but not painful.

The bottom of the FS-200 laser is then docked to the suction ring. A laser interferometer obtains the precise location of the surface of your cornea and the laser is then focused a set distance beyond that. That distance is chosen by your surgeon, but typically is in the range of 110 microns.

All said, the flap created is a predictable and consistent thickness. Made thin, it affects the tectonic strength of the cornea less than that with the bladed cuts of yesteryear. By being thin, it doesn’t disrupt the corneal nerve roots. Not cutting the nerve roots means there is less reduction of sensation. It was this reduction of sensation that led to less reflex tearing and dry eye with bladed LASIK. Net, use of the FS-200 femto-second laser implies a safer procedure with less dry eye compared to the bladed techniques (which are still used at some locations). 

Creating the LASIK flap with the WaveLight Femtosecond 200 laser

Photo-refractive keratectomy or PRK is chosen when it’s important to conserve tissue. This might occur when your prescription is large, or your cornea is on the thinner side. In PRK, the surgeon pushes the top layer of skin to the side to access the stroma. After the excimer laser, you must heal the exposed stroma with new skin. This takes about 5 days, and is made more comfortable by using a clear, thin band-aid called a bandage contact lens. PRK conserves tissue but involves more healing and more recovery time. The excimer sculpting laser is the same as with LASIK and so produces great results as well.

Optimizing Outcomes

Patients having surgery with the doctors at Wills Laser Vision at Princeton benefit from Wavefront Optimization. This means that prior to entering the LASIK surgery suite, our patients will have photos taken using the WaveLight Topolyzer VARIO Diagnostic Device (Alcon). This device captures iris recognition data, which is a map of the patient’s unique iris pattern. This information is sent to the WaveLight EX500 laser’s tracker, allowing PERFECT axis placement of astigmatic treatments. This has been a game-changer in correcting astigmatism with the utmost of precision. Additionally, the VARIO data can identify the true corneal vertex. This is especially beneficial for hyperopic (far-sighted) patients, ensuring that their treatment can be centered on the pupil center or the corneal apex. The communication between our corneal mapping analyzers and our sculpting lasers truly takes laser vision correction to the next level!

Wills Laser Vision at Princeton also utilizes the CONTOURA Vision (Alcon) system, yet another “latest and greatest” in refractive technology. This system allows the surgeon to treat each cornea’s unique topographic irregularities, which may produce a higher quality of vision. CONTOURA Vision treatments can reduce night vision problems, such as glare and halos, and can create better quality of vision than ever before. This technology is especially useful to helping patients with irregular corneas (such as corneal scarring, ectasia or keratoconus) to achieve a higher quality vision than can be done even in glasses.

The importance of a good surgeon

It is clear that there’s a lot of sophisticated technology that comes to bear to make for a successful LASIK or PRK operation. In some ways, it’s more “autopilot.” In other ways, the surgeon must pay more attention to detail and make sure all of this technology is harnessed in the most precise way for the benefit of the patient. Ultimately, the patient must trust the surgeon, and it’s the surgeon that makes the difference for a successful outcome. Personal and attentive care from your surgeon from start to finish is what distinguishes Wills Laser Vision at Princeton.


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