Technique of thickening thin cornea has come true:
Lenticule technique derived from SMILE operations is one of the most exciting developments in eye reconstructive surgery. In this method, instead of shaving and removing corneal tissue (which is done in LASIK), donated tissue is added to the cornea. To correct 6 diopter astigmatism by adding tissue, a concept called "change of refractive power based on thickness geometry" is used: 1. The alchemical mechanism of tissue (Lenticule Addition)
When you insert a lenticule with a specific geometry into the corneal stroma, the anterior surface of the cornea changes (Anterior Curvature). we take This work causes the curvature of the cornea to increase in the horizontal axis and be equal to the vertical axis.
2. Lenticule geometry for 6 diopters of astigmatism
The lens designed for this purpose is a toric lenticule:
• At 180 degrees: The lenticule acts like a convex lens (very thick in the center and thin at the edges) to create convexity.
• At 90 degrees: The lenticule acts like a plane (flat) to increase power. Refraction does not change that axis.
3. The advantages of this method compared to laser (tissue scraping)
• Reversibility: Unlike LASIK, where the tissue is permanently removed, the lenticule can be removed if a problem occurs.
• Maintenance of strength (Biomechanics): adding tissue instead of removing it, better maintains the structural stability of the cornea (especially in high scores such as 6) and reduces the risk of ectasia (secondary keratoconus).
• Treatment of corneas Thin: People who cannot perform laser surgery due to the thinness of the cornea are good candidates for these additive methods.
4. The main challenge: centralization and axis
Just like glasses, if this additive tissue is misaligned by even a few degrees (for example, it is placed at 170 degrees instead of 180 degrees), not only will it not correct the astigmatism, but it will cause irregular astigmatism, which is very difficult to correct. (Donor) and how to accurately fix it in the axis of 180 degrees?
The process of preparing and implanting this tissue, which today is known by names such as LTE (stromal lenticule extraction), is a combination of very precise laser technology and surgical skills. In the following, we will examine the steps to do this:
1. Tissue preparation (Lenticule Harvesting) The required tissue is usually obtained from two sources: Donor tissue: Lenticules removed from other patients during SMILE (for the treatment of myopia) are not discarded. These tissues are stored in the "Lenticule Bank" after sterilization and laboratory tests.
• Customized tissue: Using the Femtosecond Laser device, a very thin piece of the corneal stroma of the donor or eye bank donation tissue is cut with exactly the same toric geometry as we explained in the previous message (thick in one axis and thin in the other axis).
2. How to stabilize the 180 degree axis (Alignment)
The biggest challenge in correcting 6 diopters astigmatism is aligning the lenticule axis with the astigmatism axis of the patient's eye. For this, surgeons use the following methods:
• Pre-op Marking: While the patient is sitting (to prevent rotation of the eye while lying down, i.e. Cyclotorsion), the 180-degree axis is carefully marked on the cornea. Place it exactly at an angle of 180 degrees.
3. Surgical steps (The Procedure)
1. Pocket Creation: Using a femtosecond laser, a very thin empty space (similar to a pocket) is created at a certain depth of the patient's corneal stroma.
2. Entering the lenticule: the surgeon inserts the prepared tissue into this pocket with a special tool.
3. Spread and Adjust: The lenticule unfolds inside the envelope. Using the previous marks, the surgeon rotates the lenticule so that its thick part is exactly on the axis of 180 degrees.
4. Why is this method revolutionary for 6 diopters?
In traditional methods such as LASIK, to remove 6 diopters of astigmatism, a large amount of corneal tissue must be shaved, which causes the cornea to flatten too much and weaken its structure. But in this method:
• The thickness of the entire cornea increases.
• The optical quality of the image is better due to maintaining the more natural shape of the cornea. Surgeons calculate the exact score of the tissue with special formulas.