Refractive Surgery

The different techniques

Laser techniques 

The first lasers were retained as viable surgical options during the 1970s and 1980s, as replacements for older refractive surgery techniques, primarily represented by radial keratotomy. The use of excimer lasers for photorefractive keratectomy to correct myopia began in Europe as early as 1992 and was approved by the US FDA in 1995. 

The principle of excimer laser surgery is to modify the shape of the cornea by performing localized ablation of corneal tissue. It is intended to correct myopia, hyperopia, and astigmatism.

The excimer laser has been in use for a few years. Its very long-term effects are not yet known. Laser decentration causes bothersome side effects that may require surgical revision (double vision, image distortion, etc.). This risk is considerably reduced today by an active "eye-tracker" system that uses an infrared camera to automatically track eye movement with the laser beam, even in the event of involuntary eye movements. If the patient moves, the laser stops automatically and the system keeps in memory the exact position of the treatment. The eye is recentered and the laser continues from where it left off. 

Corneal thickness is measured before surgery by pachymetry or orbscan. Its minimum value for operating without the risk of having a cornea that is too thin afterward depends on the power to be corrected. An excessively low remaining thickness increases the risk of corneal ectasia.

Photorefractive keratectomy or PRK is the simplest and oldest technique. Simple and safe, it can be used for myopia, hyperopia, and astigmatism.

After local anesthesia of the eye, a circle of approximately 9 mm is removed from the central epithelium by scraping. The area thus cleared is cleaned and dried, and the laser can then begin reshaping. The total laser photoablation time depends on the vision disorder to be corrected and varies between 10 seconds and one minute for the treatment of mild myopia.

An antibiotic and anti-inflammatory eye drop is then instilled. Finally, a lens is placed on the cornea to protect it and allow rapid healing of the epithelium (2 to 3 days). A local treatment with eye drops continues during this period. The lens is removed after 3 days. At this stage, vision is still partially blurred and will improve to return to normal within one to two weeks.

This technique is reserved for minor optical defects and is no longer currently indicated. It has two main drawbacks: a 3-day post-operative period that is uncomfortable for the patient, and a potential risk characterized by post-operative corneal haze. 

Haze, an opacity located in the cornea, is caused by abnormal collagen production during healing. It will disturb vision and can cause a more or less transient decrease in visual acuity (one year in 5% of cases). The greater the myopia to be treated, the more likely haze is to occur. In 10% of cases, glare and halo phenomena are observed.

A modification of contrast sensitivity may also occur, which can pose a problem for certain professions (pilots, etc.).

A technique close to PRK is called LASEK: a superficial flap of the epithelium is detached from the stroma by the application of a sterile ethanol solution to the corneal surface for a few seconds; laser impacts are then applied to the surface of the cornea. The epithelium is repositioned at the end of the procedure, and a bandage lens is applied.

LASEK is comparable to PRK in terms of pain, visual recovery, and results. However, it requires specific instrumentation and is more delicate to perform. Epi-LASIK, contrary to what its name suggests, is not a LASIK. It is a form of PRK, i.e., surface laser treatment (the laser is applied to the surface of the stroma) where, instead of scraping or removing the epithelium with alcohol, it is preserved by lifting with a spatula. The flap created is very fragile and may tear. Epi-LASIK shares with PRK and LASEK, perhaps to a lesser extent, the length of recovery, the difficulty of revisions, the risks of corneal haze, the lesser predictability of healing and myopia correction. The problem of post-operative pain is not resolved.

LASIK (Laser in situ Keratomileusis) involves the creation of a thin superficial corneal lamella and laser treatment within the thickness of the cornea (in stromal layers deeper than the previous techniques). It allows the correction of greater degrees of refraction than PRK.

Instead of removing the epithelial layer, the practitioner creates a corneal flap using a microkeratome (a kind of plane with a metal blade). A hinge is maintained in order to fold this "flap" back to the edge. The laser then acts directly at the level of the corneal stroma. Once the photoablation — comparable to what is performed in PRK — has been completed, the superficial corneal flap is redeployed over the treated area, which it immediately protects. There is no need for a protective lens; moreover, this technique is painless and visual recovery is rapid: good vision from the day after the procedure.

LASIK complications are rare but do exist nonetheless. Corneal epithelial erosion may occur during microkeratome passage, mainly in patients over 50 years of age or in rigid contact lens wearers. A diffuse keratitis-type inflammation (DLK: Diffuse Lamellar Keratitis, also known as Sands of Sahara) is sometimes observed. It appears to correspond to an anomaly of unknown origin at the flap-stroma interface and disappears with anti-inflammatory treatment.

A corneal infection can occur exceptionally, with the formation of an abscess and corneal opacity that may impair vision. This complication is, however, less common after LASIK than with contact lens wear. An accumulation of epithelial cells at the cap-stroma corneal interface is sometimes present. It is then necessary to lift the flap to clean the interface and remove these cells, which give an irregular appearance and disturb vision. Ectasia (progressive bulging of an excessively thin cornea) may manifest several months or years after surgery, causing the recurrence of myopia, which will progressively worsen.

The patient may complain of glare or halos surrounding light points at night, a sensation of haze, difficulty reading in low-light conditions, or a decrease in contrast sensitivity.

These disturbances are transient and generally fade within a few months. Finally, the thinning of the cornea leads to difficulties in calculating implants during cataract surgery. This interferes with glaucoma screening and monitoring of intraocular pressure (IOP), as IOP measurement is entirely dependent on corneal thickness. 

Dry eye is common after surgery, characterized by stinging, increased sensitivity to wind, dust, or cold. It can be treated by instilling artificial tears.

Patients often opt for surgery due to insufficient tear production causing intolerance to contact lenses. However, an increase in "dry eye" symptoms should be expected during the months following surgery. Intralaser LASIK replaces the flap cutting with a microkeratome by a laser. It therefore uses 2 successive lasers. This 2nd laser completely replaces the microkeratome blade and allows the creation of a corneal flap with more precise dimensions, reducing the risks of a decentered, too thin, irregular, incomplete, perforated, or too thick flap.

Certain complications are therefore eliminated (cutting complications) or reduced: superficial corneal erosions and infections (no blade passing over the cornea), flap displacement (less oblique edge cutting), dry eye (shallower cut), infiltrate of cells under the flap, diffuse inflammation, induced astigmatism (smaller hinge).

Maximum vision is achieved more frequently than with LASIK, thanks to a reduction in astigmatism and optical aberrations that the microkeratome promotes. The ability to create a thin flap makes it possible to treat patients who have a cornea too thin to benefit from traditional LASIK. LASEK causes far fewer tissue side effects, and in particular helps reduce the incidence of induced astigmatism. Its main drawback is the possible onset of light sensitivity 3 to 6 weeks after surgery, which will however disappear after a few days of eye drop treatment.

Intracorneal rings 

They allow the correction of moderate myopia. It is a so-called "additive" surgical method: refractive correction is achieved by adding an element rather than by tissue ablation.

The curvature of the cornea is modified by the insertion of synthetic rings within its thickness. These rings create a central depression that flattens the cornea and compensates for myopia. Once in place, the rings are inert and cause little or no reaction.

These rings, or ring segments, are made of PMMA, a plastic material that is well tolerated by the living tissues of the body. The advantage of this technique is that the visual axis is not affected. Moreover, it is reversible (in case of a problem, the surgeon can proceed with the removal of the rings). The tunnels carved within the stroma thickness, into which the ring fragments are inserted, can be created by laser. Whereas until recently keratoconus was among the contraindications to this technique, several studies seem to indicate that intracorneal rings can counteract corneal deformation and reduce irregular astigmatism. The indication for intracorneal rings can also be extended to cases of corneal deformation following laser treatment.

Techniques involving opening of the globe 

These techniques are generally reserved for relatively significant optical defects or for patients whose cornea cannot respond to surgical treatment: structural defects, cornea too thin, etc. They consist of introducing an implant inside the eye whose power is determined to correct the optical defect. The placement of an intraocular implant allows surgery to be performed for a strong correction.

95% of myopia cases, up to 13 diopters, can benefit from laser treatment. Beyond this limit, this operation is no longer compatible with good visual quality. The intraocular implant, on the other hand, will deliver an excellent visual result.

The procedure involves a small incision in the eye (3 to 6 millimeters) to introduce the implant. Visual recovery is rapid (a few days). 

Several types of implants are used: anterior chamber implant with angle support (its loops rest in the angle between the iris or cornea), iris-clipped implant, or phakic implant.

Placing an implant in an eye that retains its natural lens preserves the mechanism of accommodation. In case of intolerance, these implants can be removed (intolerance to the implant may cause infections, implant displacement, or elevated intraocular pressure). The placement of intraocular implants is one of the safest and most successful procedures performed today. Clear lens extraction is sometimes performed, but many ophthalmologists believe that the risk of retinal detachment is significantly increased by the operation and that it is not reasonable to extract a healthy lens.

During the operation, the natural lens is replaced by an artificial lens of appropriate power to compensate the patient. The eye is incised and the lens extracted, just as in a cataract operation. The capsule containing the lens is, for its part, left in place: it will hold the implant. This is therefore a more involved surgery than in laser cases. In rare cases of complications, it may be necessary to remove a small fragment of the iris or to perform ablation of part of the vitreous. The operated eye is painless and vision improves very rapidly. Post-operative local care is limited to the instillation of drops and possibly the wearing of an eye shield. 

This surgery is generally intended for patients over 40 years of age; the implant can be monofocal or multifocal. It can, of course, also be applied to people with cataracts.

Just like laser techniques, the result will depend on healing phenomena. A re-intervention is sometimes necessary in the event of insufficient correction. Complications may occur: infection, retinal detachment, corneal disorder, displacement of the artificial lens, central retinal edema, retinal burn from the operating microscope lighting, or elevated intraocular pressure. 

Another option 

This is a "combined" procedure that allows the correction of major visual disorders that cannot be treated in a single intervention. The procedure involves first implanting an intraocular lens to correct the largest part of the refractive error. In a second step, LASIK is performed to correct the residual visual disorder.