The Excimer Laser
A laser is a light beam composed of parallel rays (coherent light). Its power, wavelength and diameter characterise a laser. Depending on its properties, a laser can cut, burn or vaporise the material.
In ophthalmology, we use different lasers depending on the ocular structures we aim to treat (retina or cornea).
The excitation of two gases produces the excimer laser beam (a contraction of excited dimer). Stephen Trockel, an American surgeon, developed it for eye applications in 1983. The excimer laser was the only laser used to perform ablative refractive surgery since 1985.
The excimer laser removes material (from the cornea in this case) by vaporising it. Its wavelength is in the ultraviolet spectrum (193 nanometers). In practice, the excimer laser is a device that has a series of mirrors that direct the light beam on the cornea with an accuracy of the order of two-thousandths of a millimetre (0.2 microns).
On average, each impact removes a corneal thickness of 0.2 microns over a diameter of 1 to 2 mm. The number of laser impacts varies according to the importance of the refractive disorder and the distribution of laser impacts on the cornea varies according to the refractive disorder we aim to correct.
The Femtosecond Laser
The relatively recent use of a femtosecond laser in ophthalmic surgery, and in particular in refractive surgery allows, above all, an increase in the safety of the techniques and an improvement of postoperative results. The United States by the FDA approved this laser in 1999.
It is a solid-state laser that works in the infrared spectrum and that allows us to cut the cornea according to a predetermined pattern (like we used to do with blades). Therefore, since the femtosecond laser makes blades redundant, it offers the possibility of all-laser surgery.
The femtosecond laser was invented in the early 80s. The main feature of this device is to work with extremely short pulses, of the order of femtosecond, or 10-15 seconds (0.000000000000001 seconds). This low pulse duration avoids thermal effects. The laser beam works by delaminating the material.
We use the femtosecond laser in LASIK for creating the corneal flap of the desired shape and depth with better predictability, greater safety, greater asepsis and greater comfort for the patient.
We also use the laser to make intra-corneal tunnels for the placement of rings for the treatment of keratoconus or corneas at risk. By using the femtosecond laser, we are confident that the rings will be at the same depth.
Finally, we use the femtosecond laser in the SMILE technique for creating the intrastromal refractive lenticule.
The advantages of the femtosecond laser are:
- High-quality cutting
- Precise, more shallow cutting depth for high power processing
- Decreased infectious risk
- Reduced incidents related to cutting
- The absence of induced intraocular pressure during cutting
- Possible interruption of the procedure without risks
The only drawback is the high price of the equipment, consumables and maintenance.
Laser eye surgery for myopia, astigmatism, presbyopia, and hyperopia is accurate, effective and safe since 98% of patients have a visual recovery allowing them to lead a healthy life without glasses. Postoperative vision is usually comparable to preoperative corrected vision.
The degree of satisfaction of treated patients after laser eye surgery is close to 100%. Naturally, satisfaction depends on the quality of the surgical procedure. Vision recovery requires 12 to 24 hours which allows you to resume your activities usually the day after the procedure. Screen work does not pose a particular problem, and we do not advise against it.
After surgery, the vision is changed and takes a few weeks to stabilize. During this period some patients experience near vision disturbances, which subside with time.