Surgery for myopia
Everything about the operation of myopia
Nearsightedness surgery is surgery of the eyes, made most often with a laser, under local anesthesia and on an outpatient basis (not hospital). It allows short-sighted patients no longer wear glasses or lenses. Each year, millions of short-sighted people benefit from their myopia correction by LASIK or PKR and become independent at a lens correction by far (glasses, lenses), which gives them a better quality of life.
This page is dedicated to the principles that allow to operate the myopic eyes of safe and effective. Links lead to pages containing more detailed items (ex:) Learn more about the myopia).
Surgery of myopia in a few lines:
Nearsightedness surgery caters to the short-sighted people who no longer want to wear glasses or lenses.
Techniques using the laser and re-surfacing of the cornea are commonly used)LASIK, PKR). The SMILE is to bulk remove a duckweed pre with a laser femtosecond
Both eyes are operated the same day, under local anesthesia, outpatient.
The vision improves quickly, we can rework the next day After a LASIK, and from the 3rd or 4th day After PKR.
Thecomplications are exceptionalWhen l 'indication is well put and well-executed technique.
THEastigmatism And myopia occur at the same time.
Presbyopia is not a contraindication to surgery for nearsightedness.
Principles to correct nearsightedness
The myopic eye is assigned a excess of Optical power. From light rays from a distant point source are refracted by the cornea and the lens and converge in front of the retina, then diverge, then forming a circular spot on the retina, instead of a point.
The affected eye of myopia has an excess of optical power)vergence). This excess of power or vergence is quantified by the digit "en." diopters "the prescription glasses or lenses (the symbol of the unity of diopter is D). For example, a lens-3.50 D corrects an eye which the excess of optical power is equal to 3.50 D. Do not confuse diopter and tenths: the presence of myopia (in power) reduced theVisual acuity the eye (in tenths).
If is reduced to the desired value (vergence) optical power of the myopic eye, from rays from a distant source converge in terms of the retina and the image becomes sharp. Schematically, for a myopia of-2.50 (glasses or lenses) it is necessary to subtract 2.50 D to the vergence eye to make Emmetropic patients.
Nearsightedness surgery is to reduce the optical power of the myopic eye, and make the patient Emmetropic (NET vision from afar without correction). For this, either:
reduce the optical power of the cornea
replace the lens with a less powerful implant.
Indeed, even if the main cause of myopia is an excessive length of the eye (too much axial length), it is not possible in practice to shorten the eye (IE reduce the axial length, allowing the retina to be in the plan where the light is focused by the cornea and the lens).
Site of action of surgery
(Vergence) optical power of the eye is equal to the sum of the respective powers of the cornea and the crystalline lens.
The principles of the myopia surgery differ depending on whether it is exercised on the cornea (remodeling laser to reduce his power), or the lens (replaced by a suitable power implant).
The site of action of refractive surgery depends on many parameters, including the age of the patient, the presence of a debutante cataract, etc. Once the site has been chosen, the surgeon determines the most suitable technique.
Surgical correction techniques
Schematically, the myopia operation is based on the following principles:
Reduction of the optical power of the cornea
In PKRthe correction is issued by laser excimer on the surface of the cornea, after resignation of the epithelial layer. The excimer laser sculpts the front of the cornea in order to reduce the curvature, and so the vergence.
In LASIKthe sculpture to the excimer laser is delivered in the thickness of the cornea, after cutting and a superficial corneal flap uprising. This flap is cut with a femtosecond laser.
In Smile, the femtosecond laser is used to cut "in situ" a duckweed, which is then dissected and extracted manually through a small incision.
Depending on the site of the laser issue, so there are techniques of:
– LASIK (the laser is delivered in the thickness of the cornea after cutting a flap that is reclined during the delivery of the Excimer laser)
– Smile: The femtosecond laser cuts the path of the duckweed in the thickness of the cornea. The duckweed should be dissected and then extracted manually.
– PKR (the laser is delivered to the surface of the cornea, after removing a superficial leaf: the corneal epithelium, which then regrows in a few days).
Outside the delivery site and the method of withdrawal, the volume removed for correction of the same myopia is identical for the three techniques (at least in theory, because in smile the volume of fabric is more important, because artificially increased to increase The thickness of the edges of the duckweed and facilitate manual extraction.
These techniques are carried out under local anesthesia by drops. Both eyes are operated consecutively on the same day.
Whether in LASIK or PKR, the excimer laser delivers a «» profile of ablation "that depends on the number of diopters correct: to reduce the curvature of the cornea, this profile contains a number of shots in the center of the cornea. Most nearsightedness is strong, and the deeper Central removal of the treatment is high. We can associate the correction of astigmatism with myopia: astigmatism correction is integrated into the overall treatment. Once the laser is issued, the cornea becomes "less arched", and its optical power (vergence) is reduced.
Techniques ReLEx (for "Refractive duckweed Extraction") are a variant of LASIK, the principle of which is to cut a superficial corneal flap with femtosecond laser (ReLex-Flex techic), together with the cutting (always with laser femtosecond) of a duckweed refractive Corneal (the equivalent of what would be "vaporized" by the Excimer laser). This technique is poorly realized, because if one cuts out a flap, it is better to expose the stromal tissue underlying the excimer laser and to perform a LASIK (the femtosecond laser performs a less precise work than the excimer laser for sculpture Refractive of the cornea).
The RELEX technique in its variant Smile Allows the removal of the duckweed without cutting of a flap, at the cost of a manual dissection Intracornéenne, the duckweed to be extracted by an incision of a few millimetres. The smile technique is therefore more "surgeon dependent" than that of LASIK, and its current results are comparable to those of LASIK, although longer to obtain (it takes a few weeks to a few months to obtain a visual recovery Complete with the smile technique). The ReLex techniques do not allow to benefit from certain technological advantages provided by LASIK and PKR such as selective refocusing on the visual axis, prevention of Cyclorotation,... Retouching after smile can not be done in smile. A PKR is then necessary.
Read: Smile or LASIK?
Various pages are devoted to the fundamental aspects of the correction of myopia laser, to the characteristics of laser ablation profiles, which that of simple myopia, to the simulations of correction of myopia.
Rlocation of the lens with an artificial lens implant
These techniques are based on the removal of the lens, and its replacement with an implant. The lens is removed by surgery under local anesthesia (drops): This operation is equivalent to that of cataract. Both eyes are not operated on the same day (a week apart).
The power of the implant that replaces the lens is calculated before the operated eye is more nearsighted after implant placement. The calculation of the power of artificial lens implant is called "biometric calculation" or "ocular biometry".. This technique is particularly indicated in patients over 40 years, and who have a cataract associated with a high (for example more than 12 D of myopia) myopia (see sclinical simulation and case). It is similar in its technical realization a cataract surgery.
Adding an implant of negative power into the anterior chamber or the posterior Chamber.
Indications are more rare and relate to the correction of high myopia, when it is deemed preferable not to remove the lens. The tolerance of these implants seems limited in time, to 10 years on average. In the past, there is often a reduction in the density of endothelial cells with implants of anterior Chamber, cells that are located on the back (inside) of the cornea, making the risk of corneal edema. The posterior Chamber implants, placed behind the iris, are located close to the lens and can be the cause of cataracts which require a re-intervention including the removal of the implant and the replacement of the lens by an implant emmétropisant. They give dramatic functional results in strong short-sighted, and it is best to offer patients at least 35 years of age.