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FAQ

What is the refraction defect?

Eye is an organ that resembles a camera. The main refractive part of the system is the transparent cornea forming the anterior surface of the eye. The optical (refractive) power of both the (crystalline) lens and cornea depends on their curvatures. The more convex the surface the more “diopters” these two structures have. Light beams entering the eye refract on their passage through cornea and lens and impinge on the retina, more precisely on that part of retina where the vision is most sharp. For the image forming in retina to be sharp it is necessary that both the cornea and lens have regularly curved surfaces and their combined optical (refractive) power be in harmony with the length of the eye. Disproportion between the length of the eye and the refractive power of the optical apparatus is the most frequent cause of refractive (“diopter”) errors. Short-sightedness – In short-sightedness (myopia), the eye is too long, or the combined refractive power of the cornea and lens is too high. This disproportion causes the light beam to converge (meet) in front of the retina, and the ensuing image is blurry. The error most frequently develops at school age and progresses throughout growth and adolescence. The patient with short-sightedness has difficulty to see distant objects and has usually no problems with reading. This refractive error is usually corrected with a minus (concave) corrective glasses. Far-sightedness – In far-sightedness (hypermetropia) on the other hand, the eye is too short, or the refractive power of cornea and lens is tow low. As a result of this disproportion, the beams of light meet “behind” the retina and the ensuing image is again blurry. The optical apparatus of the eye is capable of correcting this error, to a certain degree, by means of accommodation (through changes in the convexity of the lens). This possibility, however, is limited, and diminishes with increasing age. More severe refractive errors of this kind can manifest in childhood already, while a less severe error does not have to cause complaints till adulthood – the vision of a patient is then impaired for near objects, but can worsen also for distant objects as well later on. A plus (convex) glass is used in corrective glasses or contact lenses to correct this error. Astigmatism - Astigmatism is a refractive error caused by irregular curvature of the cornea or (less frequently) of the lens. The curvature and thus also the refractive power of the cornea or lens differs in different meridians (axes) and the resulting retinal image is again blurry and deformed. The error develops in childhood and is frequently combined with the basic errors – short-sightedness or far-sightedness. Astigmatism impairs vision both for distant and near objects and is corrected with cylindrical glasses or toric contact lenses. Slight degrees of astigmatism are physiological (the cornea is never perfectly regularly curved) and do not require optical correction.

What are the current possibilities of refraction defect corrections?

Refraction defects can be compensated either by the use of compensatory dioptric aids (glasses, contact lenses), or surgically – with a refractive surgery. Surgical interventions include surgeries on the cornea and intra-ocular surgeries. The cornea surface can be treated with the excimer laser, by thermocoagulation or by the use of the method of refractive incisions. Intra-ocular interventions include the extraction of the transparent lens or the implantation of the so-called phakic intra-ocular lens while the human lens stays intact.

What is the principle of the laser intervention?

The essence of a procedure that uses excimer laser consists in remodelling of the corneal tissue accomplished by a laser beam. A laser beam with a wave length of 193 nanometers impinging on the surface of the cornea is capable of delicately removing a predefined very narrow layer of corneal tissue. The energy of laser radiation interrupts the connections between individual molecules of corneal tissue so that these evaporate. Each single pulse of the excimer laser is thus capable of removing the corneal tissue with a precision of 0.25 micrometers. The distribution of the pulses is controlled by a computer with several blinds so that the tissue is gradual removed and the required change of corneal curvature is achieved along with a change of its optical (refractive power). In short-sightedness, the cornea is made flatter, less refractive in its central portion, while a procedure for the treatment of far-sightedness aims at making the cornea steeper and more refractive. The refractive error associated with astigmatism is corrected by making the irregular curvature of the cornea regular. As the excimer laser produces “cold radiation” there is no danger that the corneal tissue or other ocular structures could be damaged with heat. The high precision and good predictability of the changes in the surface curvature as well as the safety of the procedure explain why laser procedures rank among the leading methods of refractive surgery at present. Excimer laser can be also used for other treatments such as removing of surface corneal scars.

Can the laser surgery remove the need to wear reading glasses after mid-40s ?

Unfortunately not. Presbyopia is not a refractive error in the true sense of the word, but rather a manifestation of the physiologic process of ageing of the eye associated with a loss of its ability to accommodate – focus to near objects. This accommodative mechanism becomes gradually weaker starting already in childhood leading to the so-called near point becoming more and more distant (the near point is the point nearest to the eye at which an object is still accurately focused on the retina). Around mid-40s the distance of the near point shifts to a distance of about 35- 40 cm in front of the eye and the patient starts having difficulty reading or working with near objects. The error is corrected with plus “reading” glasses the dioptre value of which gradually increases with advancing age. The problem of presbyopia (i.e. the need to wear glasses for reading or work at a short distance after mid-40s) cannot yet be solved reliably with the current laser refractive procedures.

What is the difference between the LASIK and PRK procedures?

LASIK (LAser in SItu Keratomileusis) (laser-assisted in situ keratomileusis?) is a more recent and advanced method that is currently preferred at all leading centres where it is used to treat short-sightedness, mild and moderate far-sightedness, and astigmatism. The principle of the method consists in cutting away a narrow surface lamella of the cornea (most commonly 160 to 180 micrometers thick) and treatment of the tissue with laser after the lamella has been lifted off. After the deeper layers have been treated the lamella is returned back to its original site. It takes just a few minutes for the lamella to reattach and there is no need for sutures or covering the surface of the eye with a contact lens. The healing after the LASIK procedure is very rapid and practically without pain, the rehabilitation of vision lasts several days making an early surgery on the other eye possible, while the limitation of patient activities in the postoperative course is minimum. LASIK is thus a method that is more demanding in terms of its conduction, and demands also better technical equipment of the centre as well as higher degree of experience of the surgeon, but the high precision of the method, the good postoperative stability and painlessness of both the surgery and postoperative course explain why the method is preferred to PRK. PRK (photorefractive keratectomy) is a method consisting in a modification of the curvature of the corneal surface after removing its surface cellular level – epithelium. The surface of the cornea is first anaesthetised using a topical anaesthetic administered in the form of drops and the epithelium is then removed; this is followed by the laser procedure carried out in the surface layer of corneal stroma. As the epithelium layer forms a protective cover without which the eye becomes rather sensitive and even painful, the cornea must be covered with a contact lens after the procedure. Regeneration of the covering epithelium layer occurs within several days but even so the first days of the healing process of the eye are accompanied by pain and fuzzy (blurred) vision. Definitive healing of the cornea and stabilisation of vision vary to a large degree and can be expected to take several weeks to months. At present, PRK is an alternative to LASIK and is used to treat mild and moderate forms of short-sightedness.

What is Astigmatic keratotomy?

Astigmatic keratotomy („incisions of the cornea“) is a microsurgical method appropriate for the treatment (reduction) of higher astigmatism. The method consists in placing two arcuate incisions at the border of the cornea using a special diamond knife (blade). Varying the length, depth and location of the incisions the surgeon can achieve the required change of the corneal curvature and correct thereby the astigmatism. For higher degrees of astigmatism and combined refractive errors, a combination of this procedure with LASIK can be considered. As a first stage, the incisions are used to reduce corneal astigmatism, and the residual error is than approached - after the first incisions have healed and refraction has stabilised (about 6 months after the incisions) – with a laser procedure.

Is every interested person eligible for the laser procedure?

Unfortunately not. This is why all interested persons with refractive error must undergo detailed examination and interview with an ophthalmologist prior to the procedure. There are certain pathological conditions of the eye that make it impossible to carry out the procedure. Other important criteria are age and general condition of health of a patient, diseases for which he or she is treated and drugs used. All these factors might change or complicate the healing process of cornea after the procedure. General preconditions for refractive procedures are age of at least 18 years, stability of the error (i.e. the error does not 2 years deteriorate), and the absence of serious eye or general illnesses that might possibly affect the course of the procedure or postoperative healing. It is not appropriate to carry out the procedure in pregnancy or when a woman is breastfeeding her baby. It is also important to discuss the expectations of a patient and the actual possibilities of the refractive procedure with a specialist.

Can complications develop?

Similar to any other surgical procedure there is a risk of complications also with refractive procedures. This risk is minimised by careful preoperative examination, precise performance of the procedure, and observation of the principles of postoperative care. One possible “complication” is that the correction of the error is insufficient, i.e. there persists the so-called residual error after the procedure. In the majority of cases (90%), however, this residual error is minimum and does not require further correction.When needed, the residual error can be corrected with weaker glasses or the procedure can be repeated. Another possible complication is extended healing of the corneal surface which can be reduced with lubricants (artificial tears) or with temporary use of a soft contact lens. After the procedure, the eyes can be more sensitive for some time, particularly when exposed to dry and dusty environment. Rarely occurring complications may also be associated with the formation or healing of the corneal lamella, but even these complaints can be mostly managed with topical treatment (drops) or by a supplementary procedure.

Does the surgical procedure cause pain?

In the course of the procedure, the patient is fully conscious but the eye is topically anaesthetised with drops. The procedure itself is thus painless in all above mentioned methods. Patients tolerate the period of postoperative healing after LASIK procedure well. Most patients do not have any, or only minimum complaints (transitory feeling of slight burning, dry eye, slight photophobia) in the first 3-4 postoperative hours. In a vast majority of cases there is no need to wear contact lenses, a protective dressing is applied only for the first night after the procedure, and the usually rather rapid and painless healing makes it possible for the patient to return to his or her activities and work on the next day after the operation already. After PRK the sensitive surface of the cornea remains exposed. The healing process that usually takes 3-4 days is usually accompanied by increased photophobia, pain (a feeling as if a foreign body were in the eye or the eye scratched) and irritation of the eye. The pain is relieved by covering the eye with a protective dressing and the use of a treatment contact lens combined with the administration of eye drops, and possibly also of a short-term administration of a drug to reduce pain.

What will be my vision after the procedure?

After a procedure carried out using the LASIK method, the restoration (rehabilitation) of vision is rather rapid. Immediately after the procedure, the vision can be affected by the development of a slight oedema of the cornea, increased photophobia, and lacrimation, but the marked improvement of visual acuity is usually apparent on the first postoperative day already. In short-sighed patients, the transitory and intended change of correction and dioptric difference between both eyes can produce a feeling of transitory deterioration of visual acuity for near objects. These complaints resolve quickly in younger patients, but in those who have already reached the “presbyopic” age (40 years and older) the removal (correction) of short-sightedness will sooner or later be associated with a need to wear glasses for reading. A final stabilisation of vision can be expected after a month or so, with this period being slightly longer in patients with far-sightedness. In the period between the procedures on both eyes, there develops a dioptric difference between the eyes that can be corrected, should the need arise, through wearing of one contact lens on the non-operated eye, or by replacing the dioptric glass with a clear glass on the operated eye. The rehabilitation of vision after the PRK procedure lasts longer, and the vision stabilises only after several weeks to months. Laser procedures can be associated with the consequences (side effects) of decreased contrast sensitivity, i.e. the so-called “glare“ might occur in night vision – circles and a feeling of fuzzy vision around light sources, e.g. car lights. The intensity of this phenomenon depends on the degree of the original refractive error and decreases in most cases in the first few weeks after the procedure.

Is it possible to remove the refractive error completely? Can it come again?

Not all dioptric errors can be removed completely. The decisive criterion is the degree and type of the error and the preoperative thickness of cornea. The change of the corneal curvature is always accompanied by a certain thinning of the cornea. For the procedure to be safe and the eye not becoming weaker after the surgery, the surgeon cannot take away too much of the corneal tissue. In these cases (high degree of refractive error, thinner cornea), the preferable and safer choice is to reduce the error only partially. An important precondition for treatment success is also good co-operation of the patient in the course of the procedure. It is also very important for the final dioptric result that the postoperative healing of the corneal tissue is optimum (this healing tends to be individually different). It is the varying intensity of the healing process that most commonly causes residual errors – but this error is minimum in size in most cases (80% - 90%) and does not require repeated correction. When needed, the residual error can be corrected with weaker glasses or the procedure can be repeated. One of the major advantages of LASIK procedures is the rather good postoperative stability. An important precondition is that the error be already stabilised at the time of the surgery, i.e. has not been deteriorating for at least two years. In higher degrees of error, particularly in far-sightedness and astigmatism, a partial recurrence of the error cannot be ruled out completely in the postoperative period.

Are laser procedures safe in the long term?

Laser beams act on the eye only in a precisely defined region of the corneal tissue (stroma). There is no damage to the intraocular structures. A number of expert studies did not demonstrate any negative impact of the procedures on later development of other ocular diseases, e.g. of cataract or glaucoma.

What do preoperative examination amount to?

Preoperative examination is an integral part of every procedure. The examination includes obtaining general and ocular history, exact determination of the value of the refractive error, measurement of the curvature and thickness of cornea, lacrimation test, measurement of intraocular pressure, and detailed examination of the anterior ocular segment and eyeground after dilation of pupils with special eye drops. When needed, other specialised examinations are carried out as well (analysis of strabismus/squint, examination of the visual field, and other). Based on these examinations, the ophthalmologist decides whether the refractive procedure is suitable for the patient and recommends optimum surgical procedure. The patient is explained the course of the procedure and postoperative period, and when he or she wishes to undergo the procedure an appointment for surgery is made. Prior to the examination and the procedure itself, it is absolutely necessary not to use soft contact lenses for at least 3 days (in the case of “hard” contact lenses at least 3 weeks!).

What is the best time for the subsequent operation of the second eye?

In LASIK procedures, the standard interval between the operation on both eyes is 1 week (in selected cases of lower myopia (up to -4,0), it is possible to consider carrying out both operations simultaneously). In patients operated on for far-sightedness and in patients undergoing PRK procedures it is advisable to wait for about 1 month after the first procedure. It is generally not advisable to carry out the operation on the second eye before the healing and stabilisation of vision on the first eye are complete – should any postoperative complications develop it is best to postpone the procedure on the second eye.

What are the measures to be taken in the postoperative period?

One month after the procedure, you should on no account rub the eye, and any direct injury of the eye should be prevented – you should not engage in contact sports, or visit swimming pools, hothouses, solaria, and should not spend time in dusty environments or environments filled with smoke. You should pay increased attention to washing your face and hair, and limit the use of cosmetics in the first postoperative days. On the other hand, you will not be limited in carrying out the activities of daily life and there are no special work restrictions. Driving a car can be complicated in the first days as the visual activity is not yet fully stable, there is a dioptric difference between the operated and non-operated eye, and sometimes special phenomena may occur concerning the night vision (the so-called “glare“). So the best way is to behave guardedly and to observe the principle of not putting you or other people at risk.

Are there any general and eye conditions for which laser surgery is not recommended? What is keratoconus? Is it possible to treat keratoconus with laser surgery ?

This particularly concerns general conditions such as some systemic diseases, immunity disorders or advanced metabolic diseases (for example diabetes), and eye conditions such as different corneal pathologies (for example keratoconus, corneal dystrophies, abnormal corneal thickness), most forms of cataract or glaucoma, serious diseases of the iris, etc. The surgery is not recommended in patients who have had corneal herpes-like disease, or in individuals with tear production disorders. Keratoconus is a disease of the corneal connective tissue, and is bilateral in most cases. Keratoconus is characterized by the gradual vaulting and thinning of the cornea, being associated with an increase in dioptres. The condition may manifest itself as an increasing near-sightedness frequently combined with increased or irregular astigmatism. Diagnosis of keratoconus can be confirmed by a specialized examination of the cornea using ORBSCAN which is able to detect the disease in its very early stages. Keratoconus can be managed by wearing hard contact lenses, while corneal transplant is a solution for the advanced stages of the disease. Laser refractive procedures cannot be performed to treat keratoconus, i.e. they are contraindicated.

Does strabismus restrain the performance of a laser procedure?

Basically, no. However, every patient with this problem has to undergo a special strabological examination prior to laser surgery since there is a certain link between eye configuration and dioptric defects. In some cases, the correction of a dioptric defect may enhance strabismus or even induce a very unpleasant phenomenon – double vision (diplopia). Patients at risk of diplopia are not suitable candidates for a laser refractive procedure.

Is there any age limit for a laser procedure?


Refractive procedures are not performed in patients under the age of 18. There are no other age limits. However, one should realise that the correction of nearsightedness in patients in a presbyopic age group (over 40) will be associated with the necessity of using glasses for reading and work at short distances. With increasing age, the person is at higher risk of developing some of the eye diseases for which refractive procedure is not recommended (for example cataract or glaucoma, etc.).

How many dioptres can be removed by a laser operation?

This depends strongly on the type of the corneal defect in a particular patient. The laser surgery is based on the evaporation of a certain layer of corneal tissue and thus on the thinning of the cornea. In order to ensure that the surgery will be safe and the eye will not be debilitated after the surgery, the cornea cannot be made too thin. The thickness of the cornea plays a fundamental role in determining how many dioptres can be removed in a particular patient. The average thickness of the cornea in its central part (where the cornea is the thinnest) is about 550 micrometers. In such cases, it is possible to correct nearsightedness of up to ca. -9 dioptres. However, in patients with larger defects and a thin cornea it is safer to reduce the defect, or choose another method of refractive intervention (phakic lens).
Farsighted patients have rather limited choices for the correction of their defect. Laser interventions are only recommended for lower defects up to ca. +3 dioptres; it is recommended that higher defects are treated with other methods of refractive surgery (phakic lens in younger patients or the extraction of the clear lens in older patients).

How long have laser surgeries been performed in the Czech Republic and abroad?

The first laser refractive procedures were performed abroad in the late 1980s while in the Czech Republic they started to be performed in the early 1990s. The PRK method was the first laser method. Its more advanced variation, i.e. the LASIK method, has been increasingly asserted by refractive surgeons since the mid-1990s. Our surgeons have a wealth of experience with both methods – the surgeries using the PRK and LASIK methods have been performed since 1995 and 1996, respectively.

How does the surgery proceed? Will I blink during the surgery? Will I be able to move my eye?

The laser surgery itself takes less than a minute. The whole PRK procedure takes about 10 minutes, the LASIK takes approximately 15 minutes. Interventions are painless, and are performed in conscious patients after the application of anaesthetic eye drops to numb the eye. The patient will be lying down during the operation, his/her eyelids will be fixed using a dilator, lashes and the surrounding of the eye will be covered with a special sterile foil. The task of a patient during the surgery is to lie peacefully and follow the fixation point (i.e. a red blinking point about 50 cm in front of his/her eye). The position of the eye is monitored by an automatic system (eye-tracker) during the operation. The eye-tracker corrects the direction of laser impulses for minor movements, and prevents undesirable deflection of laser impulses. The modern generation of lasers uses a highly effective system of eye-tracking to correct the defect very precisely even in badly cooperating patients. The surgeon follows the operation by means of a microscope and can interrupt the procedure at any time.

How long after the surgery will I have to use the eye drops?

The duration of therapy depends particularly on the kind of surgery and on the eye’s recovery. The recovery from the LASIK procedure is very fast and the patient will apply eye drops for only 1-2 weeks. After the PRK procedure, recovery takes longer and the patient must use eye drops for several months after the surgery.

Can the laser surgery be used to treat amblyopia

Amblyopia is a relatively frequent functional disorder of visual acuity which develops in childhood, mostly as a result of strabismus, high eye defect, anisometropia (i.e. an increased dioptric difference between the two eyes) or other eye condition (for example congenital cataract, etc.). The child’s visual function develops up to the age of 6 - 8 and any impediment to the eye’s normal function in early childhood may debilitate the eye’s function for the rest of his/her life. As a result, children wear an occluder (patch) on the less impaired better eye so that the more impaired eye will “learn” to function normally. However, in some cases the eye remains permanently weaker – amblyopic. In practice, it means that the amblyopic eye is not able – even with help of the best corrective aids (glasses or contact lenses) – to achieve visual acuity (i.e. read so well) of the healthy eye. This also imposes some limitations to the potential result of refractive surgery since it can only reduce the dioptric defect rather than remove amblyopia and teach the eye to see normally again. Unfortunately, there is no method currently available (including laser procedures) to treat amblyopia in adult patients.



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