Refractive surgery brings together various ophthalmic interventions aimed at correcting certain refractive defects of the eye, so as to no longer have to resort to glasses or corrective lenses. Since its beginnings in the 80s, refractive surgery has made enormous progress thanks to technological advances in lasers, so much so that it is nowadays common procedures, especially for myopia.

A discipline of ophthalmic surgery, refractive surgery aims to correct certain refractive defects of the eye: myopia, astigmatism and hyperopia. The goal is to no longer have to wear glasses or contact lenses to correct vision.

As a reminder, the eye is made up of different elements including the cornea, a transparent tissue covering the retina. The cornea itself consists of two layers: the stroma (tissue made up of collagen fibers and representing 90% of the corneal thickness) and the epithelium, tissue made up of several layers of epithelial cells. The cornea plays an essential role in vision: like a lens, it has refractive power. It is this which makes the light rays converge so that the image of the viewed object is clearly formed on the retina. When it is too long or not long enough, or distorted, the image is no longer clear.

Refractive surgery will consist of sculpting the cornea in order to modify its radius of curvature at the center, at the periphery, in a homogeneous way or not, and thus to increase or reduce the optical power. This corneal reshaping is performed with a specific laser, the excimer laser (for Excited Dimer). It emits an ultraviolet ray whose energy, absorbed by the cornea, will allow photoablation (vaporization of the tissue of the cornea) to the nearest micron. This technique, the most commonly used, corrects:

• myopia: the eye is too long, the plane of the sharp image therefore sleeps in front of the retina, and the person sees blurry from a distance. In refractive surgery, we will therefore focus on reducing the curvature (and therefore the optical power) of the cornea, thanks to the laser;
• hyperopia: the eye is too short and / or has a cornea that is too flat. The plane of the sharp image is behind the retina, the image formed on the retina is therefore enlarged and the person sees blurry up close. The surgery will increase the curvature of the cornea;
• astigmatism: the refractive power of the eye varies according to the meridians of the cornea, which causes blurred vision depending on the viewing angle, both far and near. The laser will be used to regularize the surface of the cornea.

The excimer laser can be used in two different ways:

• the surface laser or PhotoKeratectomy Refractive (PKR): the laser is used directly on the surface of the cornea, a few microns thick, after having removed the epithelium with a small brush. The correction is delivered to the superficial stroma, located just below the epithelium. This technique is possible for low to medium myopia. It is particularly recommended for people whose corneas are thin, irregular, or with certain abnormalities (scar, etc.)
• the intrastromal laser or LASIK: a “superficial corneal flap” is produced before directly sculpting the corneal stroma, more in depth than the PKR. In practice, a small flap is cut from the surface of the cornea with a femtosecond laser (laser allowing to work with extremely short pulses, of the order of a femtosecond). The flap is lifted, then the cornea sculpted with an excimer laser. The corneal flap is then put back in place. No sutures are needed, it will heal on its own. Lasik is particularly suitable for hyperopia.

The patient should not wear the lenses for at least 48 hours before the operation, to allow the ocular surface not to be irritated on the day of the surgery.

The operation is performed by a surgeon specially trained in refractive surgery techniques.Generally, both eyes are operated on in a single operation (bilateral surgery).

Refractive surgery takes place on an outpatient basis, under local anesthesia with eye drops, possibly supplemented by a light tranquilizer. The act is painless. The patient is lying down and a special device called a blepharostat is put in place to hold the eyelids apart. During the procedure, the patient must stare at a light point.

The surgeon then proceeds with the chosen technique. Everything is computer controlled, for a minimum of intraoperative risk. Modern lasers are equipped with “Eye tracking system” or “Eye tracker”, which allow the system responsible for delivering the laser impacts to follow the eye, even if it moves a little during surgery.

The procedure takes 10 to 15 minutes per eye, but the laser itself takes only a few seconds.

At the end of a PKR, a “dressing” lens is placed on the eye.

Refractive surgery can correct certain myopia, hyperopia and astigmatism. It is the patient who expresses his wish to have refractive surgery, but not all can be operated because there are certain selection criteria. A preoperative assessment is therefore necessary to check whether the patient is eligible for refractive surgery. It has different elements:

• examinations: refraction examination (to characterize and measure the importance of the optical defect of the eye, corneal topography (to assess the regularity of the cornea), pachymetry (measurement of the thickness of the cornea), pupillometry, measurement ORA (Ocular Response Analyzer) depending on the patient.The objective is to detect any problem that may contraindicate refractive surgery, such as keratoconus (deformation of the cornea which gradually thins to take the shape of an irregular cone), or cataract Some blemishes that are too strong are also not eligible for refractive surgery;
• a medical examination concerning all pathologies, ophthalmic or otherwise, and the surgical history, in particular refractive surgery.

Refractive surgery cannot be performed in patients who are too young, because the vision must be stable for at least a year.

This assessment also makes it possible to determine which technique is best suited to the patient (between PKR or Lasik in particular).

Finally, note that this type of surgery is not covered by social security. The patient is therefore not entitled to sick leave, and no costs related to the intervention (drugs, transport, consultation) will be reimbursed.

Operative suites

The patient goes home in the evening, but must be accompanied: it is indeed not recommended to drive after the operation. Treatment with antibiotic and anti-inflammatory eye drops is prescribed for about 3 weeks. After any excimer laser surgery, it is necessary to wear UV filtering glasses when exposed to the sun. Swimming is not recommended for a fortnight

After a PKR: the epithelium grows back in a few days to cover the surface of the cornea. In the meantime, it is usual to experience eye discomfort or even pain (which usually subsides within 24 hours), and it is better to plan a few days off work. Wearing a special lens helps promote healing and reduce pain, along with taking analgesics.

After a Lasik: the post-operative treatment is simpler and less painful because the superficial epithelial layer is preserved thanks to the cutting of the flap. A light veil may persist for a few days but visual recovery is rapid, and it is generally possible to resume an activity the next day. It is very important not to rub your eyes for the first 24 hours.

The results

Depending on the type of correction, the stabilization of the optical effect provided by the laser correction occurs during the first month for a Lasik correction of myopia, and 2 to 3 months for a correction of hyperopia and strong astigmatism . After PKR, vision continually improves during the first few weeks and stabilizes by the end of the first month.

Refractive surgery allows you to see without a telescope or lens, but it does not improve eyesight. A patient with 4/10 with lenses will have 4/10 and not 10/10 after refractive surgery. In addition, even if the results are often very satisfactory today, they are never guaranteed because they depend on the quality of the healing which varies according to the individual. Additional correction by glasses, contact lenses or a reoperation is sometimes necessary.

Finally, it should be noted that refractive surgery has no effect on the retina and the fragility of myopic eyes. In myopic people, the risk of retinal detachment persists, and requires regular monitoring.

Risks and complications

Refractive surgery remains surgery, and therefore presents various risks and possible side effects:

• dry eye
• infection or inflammation
• the perception of light halo
• impaired night vision
• a split vision

The Lasik technique presents various specific risks inherent in cutting the corneal flap:

• an alteration in the shape and transparency of the cornea (healing problem which can lead to opacification of the cornea, displacement and formation of a fold of the flap). These complications are however less frequent thanks to the use of the femtosecond laser;
• diffuse lamellar keratitis (or “Sahara sands” effect), corresponding to inflammatory conditions in the space under the corneal flap;
• epithelial invasion: this early complication of Lasik is characterized by the passage of surface cells (epithelial cells) under the corneal flap, which can have repercussions on vision. This complication is more common in the event of retouching.