Deric C Simmons OD

Surgeons wanted the laser to cut more accurately and heat less tissue. That is, a much higher frequency with a much lower pulse energy. When the first femtosecond lasers appeared (modern ones give a pulse tens of thousands of times shorter than the first generation), the excitement around them immediately began.

And for good reason. At first, FemtoLASIK was developed — the same good old method of the charming and brilliant Barraker, but with much greater accuracy and without any special surprises. It was a beautiful operation, and it worked like clockwork. Actually, it still works.

With the help of a femtosecond laser, a horizontal incision is made (what was previously done with a washer that fits on the eye with a moving steel blade), then the patient is transferred under an excimer laser, a lens is evaporated inside the corneal stroma, and what was cut off at first is placed on top.

How the laser works, I have already written here.

But the laser made it possible to do something that was not possible before, namely, without” breaking ” the surface of the cornea of the eye, to cut inside, forming a cut that may not touch the surface at all. So there was FLEX — in fact, it is no better and no worse than FemtoLASIK, because there is still a flap — “flap on the leg”. But FLEX was already made with one laser, not two, so the operation was much faster, and there was no smell of “burnt cornea”, such a typical excimer. And the cut on the lens was curved, which for 2006 was a breakthrough. However, due to the high accuracy of the cut (or rather, the small thickness), sometimes there were spikes that had to be carefully separated. The lasers of that time only provided the necessary frequency, and therefore, in addition to adhesions, bridges could appear as a result of an inaccurate hit of the focus (due to microdrops of fat, for example, on the surface of the eye), they also had to be separated with a spatula.

Since we live in the world of patents, competitors of Zeiss (the laser manufacturer) began to urgently come up with their own analogues. A very good evolutionary branch was the story of superlasik, which was made using a special wavefront-eye map. All distortions are measured and transmitted to the firmware, which builds an individual profile.

The disadvantage is that part of the distortion is given by the cornea (it can be corrected), and part — by the lens. It is more difficult with him — he grows all his life, and all the advantages of the operation can be leveled after 5 or 10 years. In modern operations, the principle of an aspherical lens on the cornea is used — it is made so that it “shows” as well as possible after any number of years. Modern optimized profiles for spherical aberrations (namely, they most often create problems like “I can’t see well at night”) give better results or on a level with lasers that do not have aspherical profiles, but solve the problem according to individual profiles. If you have a Zeiss laser MEL-90 or “VISX STAR S4” from AMO, then they allow both. At the end of the operation, there is almost no difference.

Hence the myths about “3000 individual lenses in the cornea” and so on. Zeiss has updated mathematics on a new generation of its lasers, and now it is extremely difficult to catch up with it — according to at least two years of clinical research, its standard aspherical profiles are better or not worse than those specially designed for a specific operation on other lasers. Now the latter are catching up, as more complex patient training is needed to achieve the same result.

The next stage of working with corneal mechanics is FLEX. It’s the same old situ Keratomileusis, just on a different level of accuracy. Then for FLEX began to make a cut not in the entire arc, and half, and then Professor Walter Secundo and Markus Bloom decided to try to cut the lens inside entirely and get it through a small incision.

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