Nowadays refractive defects like myopia, hyperopia,
astigmatism and presbyopia (or tired eyesight) can be corrected by means of
different surgical techniques, so-called refractive surgery. These are safe and
accurate techniques that do not require admission in the hospital, nor the need
to close the eye after surgery. The interventions are painless, carried out with
topic anethesia (drops) and almost immediate visual recovery.
LASIK (using Laser Excimer)
ICL Lenses (placed behind the iris and in front of the crystalline)
The Facoemulsification of the crystalline with the implantation of a monofocal or multifocal Intraocular Lens.
The eye is the organ in charge of seeing. In order to
do so, the eye has to act like a photographic camera. To do this, it needs two
lenses to form a clear image of the outside world over a sensitive film (retina)
that instantly recives this image and, through the optical nerve, sends it to
our brain so that we can "see it". In order for this refracted image
to be clear, it must be focused exactly over the retina.
What is the myopia? And the astigmatism?
Myopia is a refractive defect that appears as a result of an eyeball extension. This gives the eye the same characteristics of a magnifying glass:
Very bad far-away vision that starts in a few meters distance from you.
Good close vision, causing a tendency to see the objects closer to you than they really are
Astigmatism is a refractive defect in which, outside the eye length, the refracted image in the cornea is upon an oblique plane regarding the retineal plane. This defect is usualy caused by an anatomical alteration of the cornea
Correction of the refractive defects
The correction of the eye’s refractive alterations
has always been made by means of optical glasses placed in front the eyes, whose
mission is to complement the power of the own eye lenses. So, in hyperopia,
where the distance to the retinean plane is smaller, or what would be the same,
the power of the lens is not enough, it is necessary to add a complementary lens
that makes its power bigger (+ glasses). For myopic people, the inverse
phenomenon happens, and therefore it is necessary to add a lens that reduces the
power of the cornea and crystalline (- glasses).
First of all, due to its construction, the field of peripheral vision allowed by the frame is restricted to a small area due to the unavoidable optical outrages that an eyeglass has on its edges.
As a consequence to the distance between the cornea and the complementary lens (glasses), it causes a size variation of the image. So, in myopic people this image is being decreased as much as the power of the lens increases, and in hyperopic people images enlarge themselves. This phenomenon can produce disorders in the tolerance of the graduation, especially when there are differences between both eyes.
Due to the glass, which is constructed upon a rigid frame, it can cause problems or incompatibility with daily life, in adition to other personal problems.
In order to avoid the dissadvantages caused by glasses,
contact lenses were developed. These are small lenses made of different
materials that are joined directly on the cornea. They have the same curvature
as the cornea in its internal face,
whereas the external face will be less curved to have a positive power (hyperopia)
or it will be flat to obtain a negative power (myopia). Its correctional effect
follows the same premise as glasses do.
They do NOT cure eye optical deffects, they only compensate the optical deffect present in that eye.
They do NOT stop myopia’s spontaneous evolution, since it is produced by an extension of the ocular globe in the back side of the eye, and lenses do not have the ability to prevent this from happening.
These MUST BE cleaned regularly and frequently, since they are made of a material that will be in direct contact with the eye.
They MUST BE removed inmediatly at the presence of minimal pain and not to try to hold it until the symptoms disappear.
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Refractive surgery basically consists
in trying to compensate the refractive deffects for life, acting directly
upon the own eye lenses, modifying its power (surgery over the cornea) or
changing it to another with the correct power (surgery over the crystalline).
The first option- a surgical intervention in the
cornea- is known as myopia syurgery. The cornea is the external lens of the eye
and the most powerful one(around 40 dioptres). This surgery consists in changing
the power of this lens by modifying it curvature, in the case of myopia,
flattening it. This way we achieve to reduce it dioptres, as many as the
flattening achieved is.
This flattening is achieved by remodeling the
cornea’s surface (a kind of corneal "polish up") with the
Excimer Laser. This laser produces a controlled vaporization over the corneal
tissue on which it is applied, and in this way the surface of the cornea can be
modified voluntarily and with exactitude.
It does NOT produce an exact correction. Its purpose is to reduce the optical defect so that the patient doesn’t have to wear glasses regularly. The laser can leave a residual defect that advises the use of correctional glasses to make some activities (driving, watching TV, etc)
It does NOT have efects over other eye structures, since the laser light only acts over the first surface "touched", so it CANNOT produce a retinal detachment, cataracts, glaucome, etc.
It does NOT "cure" myopia, it corrects it, so that typical myopic retinean injuries are not changed (they are neither improved nor they get worse).
It IS posible to reoperate an eye in the case of a myopia reapparition or if the correction has not been sufficient.
It does NOT cancel the possibility of anothery kind of intervention being made in the future.
Since 1993, a new surgical technique is being developed
to correct refractive defects. This new technique consists in introducing a
special contact lens throught a small incision (3.0mm wide) carried out in the
periphery of the cornea. This special lens is placed on the surface of the
cristallyne, between it and the back face of the iris. It can be used for myopia,
hyperopia, and astigmatism correction.
The operation is made under topic or local anaesthesia,
it does not require hospitalization, so it is an ambulatory surgery.
It is a surgical technique that doesn’t alter the eye’s ocular tissues (it is not invasive) meaning the eye structures’ physical characteristics are not modified and mustn’t have the need to heal
Functional recuperation is practically instantaneous, so eye vision is normalized a few hours after the operation – once again there is no need for healing.
The correction of instant graduation is stable, since it depends on the power of the implanted lens, and not on the changes suffered by the ocular tissues like in Laser surgery
It is a reversible process, so if the obtained correction wasn’t sactisfactory enough the implanted lens could be retired and another one with a better graduation would take its place.
EXCIMER LASER (LASIK)
Before carrying out this quirurgic intervention, a few
series of medications and controls should take place to determine the state in
which the cornea that will be treated in the operation is in. Since its shape
and thickness will be altered, its original shape must be analized. It is
essential for us to retire the contact lenses the pacient is wearing giving the
cornea the time enough for it to be normal again, since these lenses produce
physical changes upon the cornea’s surface due to the friction that takes
place, hydration changes, or small superficial oedemas. The average amount of
time needed for the eye not to be in contact with a lens varies from 15 days to
1 month.
Once it is proved with the help of a microscope that
the cornea doesn’t show any physical alterations ( scars or illneses ) and
that no ocular alterations counter-indicate refractive surgery ( cataracts and
umbalanced glaucoma being the most common ones ) a computerized corneal
topography takes place. This test consists in creating a topographic map of the
corneal surface.
A second test is carried out by means of Ultrasounds.
It finds out the exact thickness of the cornea being treated - corneal
ultrasonic paquimetry. It is essential to know if the cornea is thick enough to
be submited to this operation, since it is later on going to be reduced.
ICL LENSES
For this type of intervention a computerized corneal
topography must be done amongst an ultrasonic corneal paquimetry, also done in
Laser surgery.
By means of an optic system the existent distance
between the cornea and the pupil must
be determined, since there will have to be enough space to shelter the new lens.
The eye’s exact graduation must be re-checked, since
it is the base of the treatment that will later take place.
Anesthesia in miopía operation
A myopia operation is always made under the effects of topic anesthesia. A surface anestesia is given through Anesthesic Colirium. This way, all kinds of nuisances or pains created during surgery are eliminated while permiting a full colaboration in the surgical process when the Laser is being centered. An ansiolitic ( Deacepan ) will be adminestered some minutes before the operation through a sublingual way.
How is the operation carried out?
EXCIMER LASER (LASIK)
Nowadays there are two developed techniques for a
myopia correction by means of laser. Both use the Excimer laser, and the
diference between them is the way and place each one is applied.
SURFACE QUERATECTOMY:
The basic myopic correction technique in which the Excimer laser is used. Topic
anesthesia is always used, and once the patient is under the microscope the
ophtalmologist proceeds to remove the the thin “skin” layer that covers the
cornea ( corneal epitelium ). Once the cornea is ready and the laser programmed
the patient has to fix his eyes on a small light that will appear incide
the microscope and the laser shots will be done. This last fase lasts a few
seconds long, after which the intervention is over, the operated eye is ocluded
and the patient can go home.
LAMELAR ASISTED QUERATOMILEUSIS
WITH LASER:
The actual technique is the same as the one used in the previous
paragraph. It has the same basic principles, but is differed in the
corneal preparation before receiving the laser impacts. Instead of removing the
thin skin ( epitelium ), a small corneal lamela is cut ( approximately 0.15mm
thick ) by means of an electric microbrush, and above the corneal bed the laser
is applied. Once the polish is made with the laser, the corneal lamela is used
to recover the treated area.
As
you can see this second technique is the most complicated and laborious one, but
it remarkably reduces the recuperation period and has a more comfortable
postoperatory evolution.
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ICL LENSES
The surgical technique used is very simple: it consists
in injecting the lens through a 3.0mm incisión, same as
in cataract surgery.
Once the lens is introduced and correctly placed in the
injector, which is provided by the house, we proceed to realize the corneal
incisión under the effects of Topic or Local anesthesia, like we would do in a
Facoemulsification ( ultrasound cataract surgery). Finally, the lens would
softly be injected into the eye.
Post-operatory period evolution and cares
EXCIMER LASER (LASIK)
Due to the short length of time the anesthesic effects
of the colirium last for, it is possible that a few hours after abandoning the
private hospital your eye starts hurting lightly or intensely ( only when
surface queratechtomy has been employed ). If this were to happen, we recommend
to keep both eyes closed to avoid moving the operated one and to then use the
sedative that is prescribed after the surgical intervention. It is advisable to
use the sedative when the first symptoms appear without waiting for the pain to
get stronger. We also recommend not to exceed the suggested dose.
If conditions permit it, the eye will be left exposed
and a topic treatment with colirium antiinflamatories will be iniciated and kept
for quite a long time.
The definitive refractive effect obtained through these
surgical techniques isn’t immediately attainable, but fastened to some
cicatrization biological processes ( mending the hurt tissue, which generally
tends to re-establish previous conditions to traumatism ) As a consequence to
these phenomenons, the eye’s graduation will vary and tend to decrease the
ideal refractive effect. To avoid that the operated eye suffers from myopia
again after the cicatrization period ( about one year ), a slight
hypercorrection ( approximately 30% ) that will gradually decrease the months
posterior to the opperation will be done. These graduation changes are quite
violent along the first month, but will later become smoother.
ICL LENSES
Correcting refractive defects by means of injecting Intraocular contact lenses (ICL) is a painless technique, for it doesn’t alter the cornea’s structure. After this intervention a treatment consisting of antibiotic coliriums has to be followed. There is no need to rest nor to take special cares.
EXCIMER LASER (LASIK)
Even though it has been tried to reduce to the minimum the risk of complications taking place in these type of surgical interventions by increasing preventive and security measures, complications can happen. Some are inherent to the actual surgical technique, some others because of alterations in the patient’s biological response to the laser’s effect or to the medication used, and finally because of an accident
COMPLICACIONES MAS FRECUENTES
CORRECTIONAL ERRORS: This is the most frequent complication of them all. It is produced as a consequence to an existent difference from one cornea to the other. In the case that this residual deffect is big it can be treated by means of normal correctional methods.
CICATRICIAL HYPERTROPHIA: It is caused as a response to the laser’s agression. The corneal tissue creates some substances (collagen) that will be deposited on the treated area. They usually form a very thin and regular cicatricial material that sometimes produce an exagerated amount of cicatricial material that thickens the Collagen membrane and makes it look whiteish, causing a visual decrease, blurring images. We usually achieve to control this from happening applying antiinflamatory coliriums that produce an “atrophy” out of this material. In more severe cases the actual laser can be applied to reduce the membrane and restore its transparency.
GLARES AND HALOS: In consequence to cicatrization its intensity varies depending on the degree of corneal “cloudiness”.
DECENTRALIZATION OF THE TREATED AREA: This complication is produced when the area of the treated cornea is not centered in proportion to the visual axis, so optical aberrations will appear. In order to avoid this problem surgery is followed with a simple superficial anesthesic that provides a bright spot at which the pacient will have to look at. The ophtalmologist also has some control parameters to help avoid these accidental movements.
MEDICAL INTOXICATION: It is posible that a type of intolerance towards eye-drops used during the post-operatory period in order to control cicatrizaton is present. This problem is normally solved by suspending the use of these eye-drops and using similar ones
NON-FREQUENT COMPLICATIONS
ICL LENSES
Since it is a reversible surgery, the possible complications are avoidable most of the time, though the technique used can derive to some theoretical complications
GRADUATION MISTAKES: It is possible that a mistake is commited when measuring the eye’s graduation because of a lack of presition of the measuring instruments, or due to a variation of the eye’s graduation that happens with time (non-stabilized myopia). In this case, the implanted lens would be removed and substituted by a new one.
GLAUCOMA DECOMPENSATION: This happens as a consequence of increasing the crystalline’s total volume. The reason why ANTIGLAUCOMATISM treatment -with a laser previous to the intervention- takes places is to avoid this theoretical problem. If this measurement weren’t to be enough the lens would be removed.
CATARACTS: Because of a theoretical possibility due to the proximity of these lenses to the crystalline. If some sign were to be observed about this problem, the implanted lens would be removed.