LASIK and farsightedness
The LASIK is the technique of choice for the surgical correction of hyperopia, because this technique has benefited from the contribution of the femtosecond laser (femto-LASIK), development of techniques of centering of the excimer correction, and today sufficient. The correction of hyperopia in LASIK however has some peculiarities, and requires certain technical requirements, which this page is dedicated.
THEhyperopia is an optical defect that is caused by a defect in the couple horny + crystalline optical power. The light rays emitted by a distant source are insufficiently focused and converge to form the image in a plane located behind the retina.
In the absence of correction (lenses or eyeglasses with convex lenses, the diopter correction is positive figure, for example + 3 D), the image formed on the retina is blurred. Glasses lenses that correct hyperopia are comparable to 'lemons': they do converge light rays passing through them. The strong hypermetropes equipped with corrective eyewear eyes appear bigger.
Depending on the degree of farsightedness, this can be more or less unsightly. Hyperopia in LASIK surgery is to increase the Optical power of the cornea. The sculpture of the corneal profile laser must lead to induction of a pronounced central arch. This increase in the Central curvature allows to increase the optical of the cornea so that light incident parallel rays focus again on the retina.
As for all LASIK all laser, femtosecond laser to create a cutting with a circular coverslip (flap), who is raised to allow the excimer laser to deliver the profile of ablation correction of hyperopia. LASIK provides more precise and stable results over time as the PKR (surface laser) for the correction of hyperopia. In laser surface, the healing process is exacerbated by the importance of peripheral volume removed from the cornea, and the hypermetropique correction effects tend to fade with time. Then appears a correction, or even a regression of the effect of the initial correction. This tendency is also available in LASIK, but it is significantly reduced by the lack of interaction between the epithelium (remained attached to the flap) and the corneal stroma of the interface where the excimer correction is issued.
The hypermetropique LASIK indications
LASIK and farsightedness are so good household. There are basically two types of indications: the farsightedness of the young adult no presbyter (before age 40), and the presbyopic patient (see): presbyopia and hyperopia).
Correction of hyperopia from young adults
She is usually adults of age 18 to 35, who have a farsightedness since childhood. Correction (glasses or lenses) is of the order of 2 to 5 or 6 diopters, sometimes associated with to of theastigmatism. There is a significant percentage of case of the history of strabismus or amblyopia. LASIK is a good indication for hypermetropia correction not exceeding 6 diopters, provided that there is no surgical contraindication, and the patient has understood and accepted the postoperative of this surgery, which differ significantly from that of a LASIK for myopia.
Correction of hyperopia from of presbyopic farsighted
Installation of presbyopia is particularly embarrassing for the farsighted, because it allows more of 'offset' a low degree of farsightedness by "forcing" (IE in accommodating: presbyopia is related to a gradual reduction of cristallinienne accommodation).
To the quarantine, not only near vision uncorrected becomes blurred, but the vision by far also undergoes degradation. The presbyopic farsighted is generally a low level of "latent" farsightedness, that he compensated spontaneously in accommodating, or wearing low correction glasses occaseionnelle way (less than + 2D) in childhood or adolescence. LASIK is here a good indication because the correction of hyperopia is also beneficial for reduce the effect of on near vision presbyopia, and so the overall dependence on corrective lenses.
In particular,. the presbyopic hypermetropia correction by far is between + 2 and + 4 d are good candidates for LASIK , because the multifocalite induced by the profile of ablation of hyperopia can be optimized to allow a correction accentuated the near vision. This multifocalite can be modulated, but it is inherent in the profile required for the correction of hyperopia, which is to arch the center of the cornea in the programmed optical area, and perform a harmonious coupling with the periphery untreated.
The hypermetropia strong (more than 6 dioptres) and 60 years of age and older can benefit from the clear lens surgery with implantation monofocal and multifocal. In case cataracts, this lens surgery may subject to support by the health insurance.
Peculiarities of LASIK for hyperopia
Regardless of the context and the indication, hypermetropique LASIK is a technique that requires perfect execution, and the use of the latest technologies to allow the patient to get the best possible vision in post operative. The peculiarities of LASIK are mainly to the characteristics of the profile of laser ablation and deliverance ('technical' characteristics) and hyperopic eye ('anatomical' particularities).
They stem from the particular profile that will perform the laser in the cornea.
Ablation profile expanded
Increase the power of the cornea in LASIK, to arch the central cornea by sculpting it in its thickness, under a flap, excimer laser: this requires a broad transition zone, to avoid leaving a steep peripheral furrow in the cornea (more information on the) excimer ablation profiles).
The action area of the excimer laser is larger than for the correction of myopia, which does not impose to achieve a broad transition zone. The amount of corneal tissue required to correct hyperopia is more important than that required for the correction of myopia (in equal number of diopters). Because of this, the flap of LASIK should also have sufficient size, its diameter should ideally be greater than 9 or 9.5 mm to provide sufficient stromal surface to the issuance of the excimer correction (with the latest femtosecond lasers like the Wavelight FS 200, you can program and get a flap diameter equal to 9.5 mm - 10 mm maximum).
Degree of correction
The correction of hyperopia may be considered provided that the degree of correction in glasses does not exceed 6 diopters about. Beyond this correction, the risk of regression is important. This arises from the large volume that should be removed from the cornea to correct hyperopia. For a diopter of correction of hyperopia, this volume is significantly larger than that required for the correction of a half diopter of myopia, because of the realization of the transition area. If you reduce the diameter of the optical box to reduce the volume of ablation, may degrade the optical quality of the operated eye (a high rate of negative spherical aberration induction).
The introduction of excimer laser of the latest generation, as the laser Wavelight EC500, however to extend the indications to the hyperopia beyond 6 d, using a modulation of the corneal Asphericity intended to prevent negative spherical aberration induction. To high corrections, viewing in the corneal profile section to view the effect of the laser on the profile of ablation (inflection on the outskirts).
Large diameter of the LASIK flap
The contribution of the femtosecond laser is a definite plus; an instrument like the FS200 (Alcon Wavelight) femtosecond laser can cut components whose diameter can reach 10 mm! Obtaining a flap of large diameter is almost more of the characteristics of the cornea (initial curvature, initial thickness, etc.). With a mechanical microkeratome, the diameter of the resulting flap is most often about who was being considered, because the principle of cutting blade oscillating does not allow to control the location of the edges of the components (these are the degree of protrusion of the corneal dome in the microkeratome suction ring). For this reason,. 100% laser LASIK is the undeniably superior to standard LASIK for the correction of hyperopia and helped expand the indications for the correction of hyperopia today including the strong corrections (+ 4 to + 6 diopters). A flap whose diameter is between 9.5 and 9.7 mm can be obtained in routine and centered on the pupil through the FS200 femtosecond laser.
Thickness of the flap: do not be too late
Given the relative central savings (the periphery of the cornea receives more laser Center impacts to accentuate the corneal curvature), and the absence of risk of ectasia corneal for farsighted eyes whose corneas are usually thicker that those of short-sighted, it is not necessary to conduct a particularly fine flap. On the contrary the realization of a thin flap in LASIK hypermetropique puts them at risk of micro pleats, inflammation of the interface... Ideally, the thickness of the flap should not be less than 120 or 130 microns; a thick enough flap (140 microns) allows to marry the underlying corneal profile, and to increase the distance between the stromal and epithelial layer.
The comparison of anatomical Imaging OCT cuts high resolution allows to visualize the main anatomical elements affected by hypermetropique LASIK:
Follow-up of the eye (eye-tracking) for laser correction
The correction of hyperopia requires a number of shots laser more important than the correction of myopia. This is essentially due to the need to achieve a good quality transition zone. Because of this, track the movement of the eye is paramount, and it is necessary to have a laser equipped with a prosecution eye (eye-tracking) system performance.
The hyperopic eye cornea
The hyperopic eye is often a less arched cornea (keratometry lower) Emmetropic and myopic eye. The thickness of the corneas of the eyes farsighted is on average larger than short-sighted. These features are not a problem in case for the use of the femtosecond laser, which must be the rule for this type of indication.
Axial length and accessibility of the eye
It's also more short (low axial length), and because of this is usually less "bulge" one eye myopic (called enophthalmos). This anatomical particularity is not truly a problem with femtosecond laser cutting techniques, because the head unfortunately footprint is less than that of the microkeratomes. A marked enophthalmos can be difficult to insert the suction ring, if the orbital opening is less than 20 mm.
Nasal pupil, wide angle Kappa
The pupil of hyperopic eye is often located more in nasal IRIS than short-sighted. Kappa angle is greater. The Visual axis 'pass' in nasal pupillary area (the pupil of entry is formed by irien opening image seen through the cornea): it is recommended to focus the excimer treatment in the direction of the corneal vertex. Therefore, it is important to use a technology of centering the treatment allowing to take into account these peculiarities. Iris recognition, the location of the vertex (referred to sometimes as "apex"), are available on some platforms of the most recent.
For the cutting of the LASIK flap (FS200) latest femtosecond laser allows rapid refocusing of the cutting path before creating this one, and without any reduction in the diameter of the flap.
For the issuance of the excimer laser treatment, the Iris recognition and prevention of the pupillary shift are performed through a measure topographic and pupillary preoperative (Topolyzer Vario) and iris recognition of the EX500 (Alcon Wavelight) laser. This is particularly important to avoid the risk of decentering, and optimize the optical quality of the eye after surgery (see the) page dedicated to the centering of the EX500 excimer laser treatment). A shift of the photoablation to the corneal vertex must be systematically made in angle kappa pronounced case.
The following video highlights all processes to optimize the result of correction of hyperopia (strong in the present case) in LASIK:
Postoperative hypermetropique LASIK
The result of the hypermetropique LASIK differ from that of myopic LASIKbecause of the characteristics of the profile of ablation, and the fact that the existence of an initial over-correction, which, although it is desirable to anticipate on the phenomena of healing (which "how to" part of the effect on the cornea), makes the patient myopic and embarrassed in vision by far. A page is devoted to the General description of postoperative care after LASIK.
Postoperative LASIK at the young farsighted
Based on the existence or not of an over-correction (sometimes voluntarily induced to anticipate a premonition scar regression as important), the initial impression is an overall improvement, with ease especially felt in near vision, but the perception of "vagueness" in vision by far. This is partly related to the fact that 'very far' vision is relatively considered very clear by moderate hypermetropia (up to + 3D about). There is a sensation of vision a bit 'Misty' for a few hours to see a few days. After a few days, the vision by far found increasing sharpness, and the "Haze" or the "light veil" felt dissipates over time. It takes at least three months to judge the results of the correction after a hypermetropique LASIK! Dry eye and bright halos also tend to shrink over time. It is important to regularly moisturize the eyes with artificial tears, eye gel, etc. The hypermetropique LASIK does not increase or return of a former strabismus, surgery or not. The effect of LASIK on the look is the same as that provided by contact lenses.
Postoperative care of LASIK in the presbyopia farsighted
The induction of an over-correction on the side of the non-dominant eye generally allows the patient to feel an improvement of vision closely on this side; the possibility of an increased multifocalite allows also to strengthen one side of the dominant eye. Good vision recovery seems far more delayed even more as part of a surgery of the young hypermetropic, especially for patients with hyperopia is low initially (less than 2 diopters). It is necessary wait several weeks, until about three months before judging the final result. Vision by far is usually slowly improving but surely over the days (regression of a part of the treatment effect gradually erase initially induced sur-correction effect).
Hypermetropique editing after LASIK
In all case, one editing after LASIK may be considered after a delay of 3 months or more, in case of persistent over-correction, or on the contrary, if the treatment is to start under corrector. After hypermetropique LASIK alterations are more frequent than after myopic LASIK, especially if correction is important and is accompanied by a pronounced astigmatism. For editing is to re - raise the flap, and deliver additional correction, before you reposition the flap.