Laser correction of eye defects

Laser surgeries can completely remove optical disorders or at least significantly reduce them. Those are methods of so-called refractive surgery. They gradually develop, become more gentle and effective.

Optical defects

If you look into the distance healthy eye without any eye defect sees infinite distant object sharply on the retina, i.e. the focus is located exactly on the retina.

Shortsighted eye is caused by increase of the eye’s axial length (1 mm of prolongation means approximately 3 diopters) or by great refractive optical power. The reasons are usually genetic factors, excessive eye exercise in adolescence and others..

Longsighted eye has short front-back axes or insufficient refractive optical power. It is a congenital disorder, very often genetic. Its values usually range from +2 to +6 diopters. A longsighted person can at first see quite well. With adding years he/she can see worse close objects and in some time even distant objects.

Astigmatism – irregular curvature of the cornea and often appeared in combination with above mentioned defects.

Laser surgeries

The principle of different methods of laser surgeries is identical. Laser changes the curvature of cornea with the help of special beam – it remodels corneal tissue. In optical defects the beam of light coming into the eye does not end up on the retina, where there is the sharpest vision. It is located either in front or behind the retina. Laser surgery can change optical power and curvature of retina, so that the beam of light coming into the eye would get exactly on the spot of the sharpest vision, on the retina.

In case of myopia the retina is thinned in the centre. The curvature of the surface of the eye changes, which causes focus of the beam of light on the retina. In case of hyperopia the outer part of the retina is removed, which increases the central curvature. In patients with astigmatism is the cornea modeled irregularly according to the type of the curvature of the surface.

The selection of particular surgical technique depends on the amount of diopters, type of refractive defect, thickness of the cornea, age, state of health and patient’s wish.

The patient should be examined before the surgery at a special eye clinic. A needed optical correction is measured and the cornea is examined in detail. It is necessary not to wear contact lenses at least two to four weeks before the examination (according to type of lenses). It prevents the examination from distortion.

A condition for the surgery is age over eighteen, stable optical defect for at least two years, good general state of health and absence of other eye disease. The surgery is not performed in patients with severe disease, in pregnant women or women that breastfeed (hormone changes can cause instability of optical defect). Laser surgeries are performed out-patiently. Eyes are anesthetized with drops. A blepharostat is put on the eyelid and the actual laser procedure is performed.

Among most common laser procedure used for correction of refractive defects belong: PRK – Photorefractive keratectomy, LASIK – Laser-Assisted in situ Keratomileusis, LASEK – Laser-Assisted Sub-Epithelial Keratectomy, epi-LASIK and femto-LASIK.

PRK

The oldest known method, which can be used for treatment of optical defects. Excimer lasers are used and the process is very similar to LASIK method. The difference is that by PRK a thin layer of epithelium is removed from the retina before the laser treatment. It is used when the retina is too thin and LASIK is not suitable. PRK still develops and improves. The newest generation of excimer lasers forms much smoother surface of the treated area and increases significantly the effectiveness and exactness of the procedure.

After anesthesia of the eye a surface of the epithelium of retina is removed and then the actual laser procedure is performed. The procedure takes short time. After the surgery ATB drops are applied into the eye. The eye is plastered and the patient can go home. To cover the eye even contact lenses can be used. The disadvantage is longer recovery period and pain after the surgery. The advantage of this procedure is minimal invasiveness and safety.

LASIK

The treatment is suitable for patients with hyperopia, myopia and certain level of astigmatism. Sometimes it is harder to perform the surgery in case of eyes with short eyelids or high superciliary arch. The principle of this method is laser photo ablation in deeper layers of cornea after creation of corneal flap. By the surgery an incision is lead in the cornea with the help of microkeratome and a flap is formed, which in certain part fixed with the cornea. The flap is then lifted up or in the direction of nose and a laser correction is performed. After that a flap is put back on the original place. A preservation of sufficient thickness of cornea is important. After the end of the procedure ATB drops are applied into the eye and the eyes are then covered with so-called shell (protection against injury). The advantage is no pain after the procedure, significant stability of final correction, absence of retinal opacity, fast return of optical functions.

LASEK

The surgery is used by not heavy myopia, hyperopia and astigmatism. This procedure is also similar to PRK method. The flap is formed out of upper layers of cornea with the help of 20% ethyl alcohol (in patients with PRK is the thin layer of epithelium removed completely). An epithelium flap is formed, which is partially connected to cornea. The flap is then remodeled and put back. The eye is covered with contact lens that stays there for several days. The advantage of this method is painlessness and fast healing process.

epi-LASIK

Method similar to LASIK but on the cornea a very thin flap is formed. It is formed with the help of epikeratome and only small layer of outer corneal cells are separated. The cornea is at the end of the surgery covered with contact lens for several days. The healing process is slower compared to LASIK and can be even painful. The method can be used in patients with very thin layer of cornea.

femto-LASIK

It is a LASIK method, which is performed with femtosecond laser. With its help a thin flap of approximately 100µm is formed on the eye and the eye defect is then corrected with another laser underneath it. The treatment is very gentle because the head of femtosecond laser does not touch the eye; it is only applied to it. The formed flap is very exact and it is possible to choose better its size and shape. The incision is not made through cut but with laser beam, which is controlled by computer. The part of the surgery performed by femtosecond laser lasts only 35 seconds. The technique is more precise, gentle and safer than other LASIK surgeries, when a mechanical device is used.

The vision returns back to normal in all laser surgeries in four days according to the type of a surgery. To stabilize the defect last three to six months. The surgery can be repeated if there is any left defect although only after healing process and stabilization.