Laser vision correction

EXCIMER LASER SURGERY for VISION CORRECTION was performed for the first time in Croatia by assoc. prof. Nikica Gabrić at the Eyeclinic „Svjetlost“ in Zagreb at the beginning of 1998. From January 2007 our Clinic has the best excimer laser that represents the final reach of the technology so far - Allegretto EQ-400HZ. With this laser that uses the most sophisticated software and wavefront analysis, we can treat not only shortsightedness but also astigmatism and longsightness. Prof. Gabrić himself conducted surgery on the same laser to his own eyes, because previous technology did not give good results for the patients with high astigmatism. He has no longer the necessity of wearing glasses or contact lenses.

We continue to follow improvements in technology and in laser treatments. On April 2nd 2009 the new era of laser vision correction has begun in Eye Clinic Svjetlost: the Z-LASIK procedure. New successful operations have been performed on the ZIEMER FEMTOSECOND LDV LASER (Leonardo Da Vinci) in combination with Allegretto excimer laser. Z-LASIK procedure consists of two steps that are both automated and computer guided on two lasers. First step of the Z-LASIK procedure is performed on the new FemtoSecond LDV laser that is used to create corneal flap without mechanical microkeratome. With the FemtoSecond laser surgery becomes completely automated and precisely computer guided (FULL LASER TREATMENT NO BLADE LASIK), enabling patients more comfortable, faster and completely painless treatment and recovery. Second step of laser vision correction is performed on Allegretto excimer laser that is used to reshape the surface of the cornea. Therefore, Z-LASIK procedure enables through both steps optimal and painless treatment that is completely automated and computer guided.


Excimer laser is highenergetic UV laser that is being used in ophthalmology for many years. Word excimer derives from excited dimers and indicates induced molecules of gases – argon, xenon and krypton and of halogens – fluoride, chloride, bromide. First researches on the application of excimer laser on animal model began in 1975 (Velazco and Sester), while first operation on human eye was performed in 1986 (Seiler, McDonald). Excimer laser vision correction is surgical procedure that uses cold light ray to reshape the cornea. Pulsating light removes the microne amounts of corneal tissue with the utmost accuracy.

Nowadays four excimer laser techniques are being used in the world, and all four of them are available in Eyeclinic „Svjetlost“ and can be performed on Allegretto laser:

• Fotorefractive keratectomy – PRK
• LASEK
• EPILASIK
• LASIK

On this new laser with significantly improved software refractive errors from +5.00 to -10.00 and up to 5 cylinders can now be corrected.

Am I a candidate for laser surgery?

Every patient that has refractive error within this range can be a suitable candidates for laser vision correction, but detailed ophthalmic preoperative examination is necessary to assure that there aren"t any contraindications. Also, people over 40 years of age can correct their distance vision with laser surgery but they"ll require the near vision spectacles like all their coevels. Technology is in constant progress and there will soon be solution for this problem as well.

Preoperative examination that determines whether the person is suitable candidate for laser surgery consists of:

• determination of visual aquity without spectacles
• determination of refractive error on automatic computer refractometer and testing visual aquity with obtained correction
• measuring of eye pressure on the non-contact tonometer
• examination of front and back eye segment on a slit-lamp
• computer corneal topography (scanning corneal surface to see if there are any abnormalities) – WAVELIGHT ALLEGRETTO OCULUS PENTACAM II
• front optic coherent tomography (VISANTE OCT) to establish thickness of the cornea and possible abnormalities in its structure
• IOL Master axial length measurement (the length of the eyeball)
• automatic computer refractometry in mydriasis (with dilated pupils)
• The whole preoperative examination lasts for 30-45 minutes and determines whether the patient is suitable for laser vision correction.
• None of the examinations is harmful to your eye in any way. The only discomfort are dilated pupils and for that reason patients can have blurry vision for two hours after the examination.
• Doctor and patient will decide together upon the technique that will be applied for laser vision correction.

REFRACTIVE ERRORS

• from 0.00 to -7.00 – PRK, LASEK, EPILASIK and LASIK techniques are being used
• from -7.00 to -10.00 – LASIK technique is being used
• over -10.00 – laser technique can"t be applied so we perform refractive surgery with IOL implantation
• from 0.00 to +5.00 – LASIK technique is being used

Neither PRK, nor LASIK technique is painful during the procedure. The main difference between these two techniques is in the post-operative recovery – first three days after PRK technique patient can feel slight itching until epithelium heals up. On the other hand, after LASIK technique, there is no pain and complete recovery is faster (after only 3 days, patient can go back to work if he doesn"t work in unfavorable conditions such as exposure to dust, wind or heavy manual labor).

So, in cases when both techniques can be applied, patient will decide which technique he prefers. But as we have already mentioned, in some cases, depending on refractive error, only one type will be applicable (e.g. for refractive errors + and >-6.00 only LASIK can be performed).

Scanning laser ray passes through the system of lenses - reflecting mirrors, filters and focuses on the cornea surface under computer guidence. Before the procedure, an engineer checks upon caliber parameters of the laser itself and measures appropriate laser energy to adjust the computer settings on the amount of applied energy power.

On the day of the surgery patient comes to our Clinic without any special preparations. Anaesthetic drops are applied to the eye and patient waits for the surgery. Then he/she is ensconced on the laser table. After that, depending on the technique, epithelium is removed or corneal flap is created (neither of those procedures are painful). Then surgeon focuses laser ray on the centre of the cornea and patient fixates blinking point over his/her eye. Controlled by the foot pedal, laser ray begins to reshape the surface of the cornea, which in average lasts approximately 30 seconds, depending on the refractive error. This procedure is completely painless. It is necessary to say that special eye-tracker monitors possible movements of the eyeball to ensure that the effect of the laser eye beam targets specific parts of the cornea.

Eye-tarcker

After the procedure that doesn"t last more then 15 minutes for both eyes, patient will get protective soft contact lens. The vision will be tested right after the procedure so the patient can see immediate improvements. The patient then goes home without any pain. After the PRK technique, soft contact lens stays on the eye for three days and the drops will be applied to the eye for several months. After LASIK technique, soft contact lens isn"t always needed, but when given, it stays on the eye only one day, and drops are being applied to the eye for one month.

In case of myopia (shortsightedness) rays of light fall in front of the retina either because of too strong fracture strength of the cornea or because the eyeball is too long. To enable the rays of light to fall directly on the retina it is necessary to reduce the curvature of the central corneal zone. That can be achieved by removing the minutest layers of tissue (cca 9 microns for 1 diopter) in the centre of cornea. Minus spectacles have the same effect – they reduce the fracture strength of the cornea.

In case of hyperopia (longsightedness) rays of light fall behind the retina either because of too weak fracture strength of the cornea, or because the eyeball is too short. To enable the rays of light to fall directly on the retina it is necessary to reinforce the curvature of the central corneal zone. That can be achieved by remodelling the peripheral zone of the cornea to consequently achieve the intensified curvature of the centre. Plus spectacles have the same effect – they increase the fracture strength of the cornea.

In case of astigmatism, due to various curvatures of corneal meridians, laser ray reshapes only the curvature of the meridian that is the bearer of the refractive error.

 

 
After the procedure the image of an object falls directly on retina.

Laser vision correction is in clinical use for more than 20 years now and milions of people from all over the world have been operated using this method. The only complication of this procedure can be regression of one part of the corrected refractive error or appearence of the slight scar. Both of this complications can"t lead to the lost of vision and can"t be predicted because they depend on individual tissue healing potential of every patient. Postoperative scar does not decrease significantly vision sharpness and can be cleared with corticosteroid drops. Regression of one part of the corrected refractive error can be treated either with additional laser surgery or by carring spectacles. We have to say that over 95% of patients have no difficulties after the procedure, neither with regression of the refractive error, nor with scar tissue appearence.