Which is safer, full femtosecond or semi-femtosecond?

First of all, don't be confused by the names of full femtosecond and half femtosecond. Is full femtosecond necessarily better than half femtosecond?

breakdown

Why is full femtosecond called full femtosecond? Because it only uses femtosecond lasers.

Why is semi-femtosecond called semi-femtosecond? Because it uses two kinds of lasers (femtosecond laser+excimer laser).

So if we change our names.

Full femtosecond, we call it a single laser.

Semi-femtosecond, we call it double laser.

Is this the other way around-double lasers sound higher.

Therefore, in fact, there is no full femtosecond or semi-femtosecond name in formal occasions, which is more in line with the marketing price increase.

What is a femtosecond laser?

Femtosecond laser is the shortest pulse that human beings can get under laboratory conditions at present, and its instantaneous power is greater than the total power generated in the world. Because of its high speed and high resolution, it is very suitable for cutting corneal tissue.

Semi-femtosecond surgery and full femtosecond surgery are different ways to cut corneal tissue.

The subtleties of the cornea

Cornea and corneal structure map

Cornea is a transparent part in the front of the outer layer of the eye wall, which is irregular and round, accounting for one-sixth of the outer layer area, and is about 1mm thick. It is mainly composed of connective tissue and has no blood vessels. As shown on the left.

The radius of curvature of the anterior corneal surface is 7.8mm in the horizontal direction and 7.7mm in the vertical direction.

The radius of curvature of the posterior surface of cornea is 6.2 ~ 6.8mm；;

Corneal thickness varies in different parts. The central part is the thinnest, with an average of 0.5~0.57mm, and the peripheral part is about1mm..

The cornea is divided into five layers: from the outside to the inside: the epithelial layer, the anterior elastic layer, the matrix layer, the posterior elastic layer and the endodermis, as shown on the right.

What is the essence of laser myopia surgery?

Simple understanding: the essence of myopia surgery is to regard the intact cornea as a transparent glass and carve a pair of glasses that meet the individual on the glass.

Although the cornea has five layers, the middle stroma layer accounts for 90% of the corneal thickness, so this layer is considered as an ideal position for carving glasses. The main difference between full femtosecond and semi-femtosecond lies in how to reach the matrix layer.

What are full femtosecond and semi-femtosecond?

Usually called full femtosecond, it is actually called micro-incision matrix lens extraction, and English is small-incision lens extraction, abbreviated as SMILE.

Femtosecond laser passes through the epithelial layer and the anterior elastic layer, directly cuts the tissue on the matrix layer to form a lens, then cuts a small hole (2-4mm) from the side with femtosecond laser, and finally takes out the lens from the small hole position, and it is finished. The video flow is as follows.

Full femtosecond

Usually called semi-femtosecond, it is actually called femtosecond laser-assisted excimer laser in situ keratomileusis, and the English name is Femtosecond-LASIK, or FS-LASIK for short.

Femtosecond laser cuts a circle around the cornea, leaving a pedicle. Then open the corneal tissue, commonly known as corneal flap. Then excimer cutting is carried out on the matrix layer, and the corneal flap is covered back to its original position after cutting. The video flow is as follows.

Semi-femtosecond

When you understand what is full femtosecond and what is semi-femtosecond, let's see how to choose.

How to Choose Full Femtosecond and Semi Femtosecond

Scope of revision:

Full femtosecond: myopia

Semi-femtosecond: myopia

Therefore, the correction range of semi-femtosecond is much wider than that of full femtosecond, and it is likely that many people are not suitable for doing full femtosecond only.

High-order phase difference (HOA):

Full femtosecond can't correct the high-order phase difference that affects night vision, but half femtosecond can. In fact, full femtosecond may also cause additional higher-order phase difference. So if you care about night vision and high-order phase difference, please choose full femtosecond carefully.

Postoperative healing:

There is no need for corneal flap in full femtosecond, only 2-4mm incision, and corneal flap in half femtosecond, with 20mm incision. All postoperative healing is faster under full femtosecond. It is more suitable for patients who need to use their eyes immediately after operation.

Risk of infection:

Similarly, due to the semi-femtosecond corneal flap and incision area, the infection probability of semi-femtosecond is greater than that of full femtosecond, and full femtosecond has no complications related to corneal flap. However, due to the full femtosecond operation in the matrix layer capsule, once infected, the treatment difficulty is greatly increased.

Operation difficulty:

Full femtosecond surgery has a long learning curve and short development time, which tests the doctor's operation level. Semi-femtosecond is easy to learn because of its long clinical time, and the requirements for doctors are not so high. Therefore, all femtoseconds should make an appointment with a trusted doctor.

About low degree:

One of the main steps in full femtosecond is to remove the lens. If the degree of myopia is too low, the lens will be thinner, so the lens will be more easily broken and difficult to take out. Therefore, Lao Yi, who has a low degree of myopia, suggests carefully choosing full femtosecond.