This article has been provided by Dr. Huseyin ACAR to give information about ‘Refractive Surgery’ in general terms.
HOW DO WE SEE ?
Main function of our eyes is to perceive the incoming light and to transmit data with the help of optic nerve into the visual centers of our brain. This function is realized by various embodied structures. In the simplest explanation, incoming light passes through a system of lenses and then is focused upon nerve layer located at the back side of the eyes. These lens system consists of our cornea located at the front side of our eyes and intraocular lense located inside of our eyes.
WHY DO NOT SOME PEOPLE SEE WELL ?
A situation, as we call refractive errors, happens in case that lens system of our eyes could not focus the incoming light rays upon nerve layers for a number of reasons. The main reasons for refractive errors arises with the facts that our eyes may be longer than ‘normal’ and refractive level of cornea may be lower of higher than it must be. If the lens system refracts the light in more than it is required, then myopia occurs or if it refracts the light in less than the required amount, then hyperopia occurs. As for astigmatism, the light is focused upon two different points.
It is required to change the refractive nature of the lens system in the eye in order to correct refractive errors. The ways to correct these defects are to wear eyeglasses or contact lenses or to perform surgical methods.
Image 1 :Refractive errors (vision defects) happen in case that lens system of our eyes could not focus the incoming light rays upon nerve layers for a number of reasons
WHAT ARE THE WAYS TO GET RID OF USING EYEGLASSES AND CONTACT LENSES ?
The methods of getting rid of using eyeglass or contact lenses can be categorized into two main groups. One of them is the operations applied to the outer side of the eye or namely to the cornea. Firstly I would like to give some information about treatment methods applied to the cornea. The methods used for the cornea are excimer laser and SMILE technique. The main principle in the excimer laser is to change curve structure of cornea by reshaping it. At first, refractive error of the patient is calculated and these values are transferred into the excimer laser device and the device then determines what should be the new curve of the cornea by implementation of various techniques and accordingly it reshapes cornea’s curve finally. Cornea consists of various layers and excimer laser is administered to the stroma layer located just under the epithelial layer which is the uppermost layer of cornea. Excimer laser technique can be categorized in two main groups, PRK and LASIK, according to the methods applied to reach to the stroma layer. In PRK method, firstly epithelial layer is removed by spatula, alcohol or laser and then excimer laser is performed to stroma layer. After operation, epithelial layer renews itself within 4 to 5 days. Patient does not feel any pain during procedure but afterwards foreign body sensation and pain may follow for one or two days. In LASIK method, epithelial layer is not removed but instead a cover is formed in cornea as to contain corneal epithelium and a little bit of stroma layer. While this cover was formed by knife in the past, today this method has almost been completely altered by a system named as femtosecond laser technique. In LASIK method, it is reached to the lower part of the stroma layer by forming a cover with the help of femtosecond laser and then curve of the cornea is arranged by implementation of excimer laser technique into this area. After the procedure is completed, the cover is reattached again. LASIK technique has minimum pain and foreign body sensation levels as epithelial layer is not removed and these side effects just last in a few hours.
Image 2 : In PRK method, epithelial layer is removed and then excimer laser is performed to stroma layer.
The second technique performed on cornea is SMILE technique. In this method excimer laser is not used. Instead, femtosecond laser, which is used to form a cover at LASIK technique, prepares a piece of tissue inside of cornea and surgeon removes out this tissue through a formed cut. In this way, the curve of the cornea has been modified.
All the techniques I mentioned about PRK, LASIK and SMILE are the operation methods to the cornea by using lasers. Now I would also like to mention about the operations performed by entering inside of the eye. These are the operation to insert lens inside of the eye and to alter the ocular refractive status. Inserting lens inside of eye is mostly preferred for the patients of high myopia that are not suitable for a laser operation. Preserving current lens of the patient, an artificial intraocular lens is installed just in front of the existing lens. Roughly you can imagine that a contact lens will be installed permanently inside of the eye. However, this artificial intraocular lens inserted inside of the eye has different material properties compared to the contact lens and it has the ability to remain inside of the eye for life-long period.
Image 3: In LASIK method, stroma layer is reached by forming a cover and then curve of the cornea is arranged by implementation of excimer laser technique into this area
Removing natural intraocular lens and implanting an artificial intraocular lens is generally used for the patients who have difficulties for both short and long sightedness or are above 40 years old with the problem of shortsightedness. In this operation, our intraocular lens is removed and instead an artificial intraocular lens is inserted into this area that enables patient to see short, medium and long distances.
HOW TO UNDERSTAND THE SUITABILITY TO THE REFRACTIVE SURGERY ?
The most critical stage in refractive surgery is the determination of whether a person is eligible for treatment or not. According to the research, about half of the patients who applied to the laser centers are not suitable for the laser operations for some reasons. There are many factors affecting the suitability of getting the laser operation and the choice of the correct method. First of all, the patient’s refractive error is determined by examinations and tests. It is then checked whether the cornea has sufficient thickness for this correction or not. If the patient’s cornea is suitable for the laser operation, then the most appropriate method is decided with the patient; taking into consideration of age, work, hobbies and other factors. In cases where the eye is not suitable for the laser operation, installation of a lens inside the eye or intraocular lens exchange is on the table. Again the necessary tests are made related to these matters and the most suitable method is found for a specific patient.
SUMMARY
Refractive surgery is the whole of all methods used in getting rid of wearing eyeglasses and contact lenses for the people who have to wear them to see the short, medium and long distance. Techniques in refractive surgery can be divided into two groups as the methods applied for the outer side of the eye or namely for the cornea and as the methods applied to the interior of the eye. Generally, the first option is applied to the outside of the eye or the cornea. If the cornea is not suitable, intraocular operations are other options.