PRK and trans-PRK
The above-mentioned operations are utilized for correcting reflective defects of the eyes including myopia, hyperopia, and astigmatism. These operations are performed on the cornea and with transformation that they develop on the cornea they cause focus and transparency of images in the eyes. The operation has two stages: in the first stage a thin layer of the corneal surface is removed and in the second stage using a special laser device known as Exmier laser the desirable changes are created on the cornea. Although the second stage of operation is the same across all techniques and is performed by Eximer laser, the first stage which is the stage of corneal preparation performed with different methods and naming of this operation as LASIK, PRK, and the like are usually performed based on the first stage.
PRK and Trans-PRK operations are considered as superficial operations, because in these operations in the stage of preparation, only the coating layer of corneal surface which is called “epithelium” is removed and there is no incision in deeper layer of corneal which is called stroma, unlike Lasik in which an incision is created and the stroma and a flap is developed. Therefore, from this aspect, this operation is safer. However, these operations have their own problems which are mentioned in subsequent sections and in the page of selecting the type of surgery.
The following figure represents a view of cornea and its layers as well as that stage of radiation and collision of laser beams to the cornea during operation.
The first method for correcting vision is PRK laser whose background is more than 20 years. At the beginning, this type of operation was performed for all scores of vision. However, later it was found that at higher scores the cornea becomes turbid. Therefore, for some time, this operation was replaced with LASIK. However, today thanks to improvement in devices and applying special drugs during the operation, the chance of corneal turbidity has been minimized and due to several advantages of PRK, this technique has regained its popularity.
In this operation, first the coating layer of the corneal surface known as “epithelium” is removed manually and then laser beams are radiated to the cornea. Eventually, a dressing lens is incorporated on the cornea to accelerate the healing. This lens should be removed after some days. After the operation, within some days, “epithelium” is restored again and coats the surface of cornea, but the transformation of cornea remains as earlier. Among the advantages of this method is that there is no incision on the cornea, thinner layers of cornea are removed and therefore the strength of cornea is less damaged. This operation is suitable for most individuals especially those who have a thin cornea. However, one disadvantage is that due to delay in corneal healing, return of vision to the patient is slow and the patient has pain and discomfort in the eyes for several days. Nevertheless, PRK can be considered as superior than other operations in terms of safety.
Trans-PRK is very similar to typical PRK and has all the advantages of PRK. However, unlike PRK, the epithelium of the cornea is removed with laser instead of manually, and as such this operation is a full laser operation. Eximer laser first removes the superficial layer of cornea (epithelium) and then scrapes the cornea as much as required. Therefore, layer removal is performed with the maximum accuracy and at minimum extent. The advantage over typical PRK is that the healing occurs faster and the pain and discomfort following the operation may also be less. Unfortunately, this operation cannot be performed at very low scores.
Currently, this operation can be done only with the brand of the device available in Parsian clinic. This center is proud to provide clients with this operation on a wide range for the first time, and in terms of this it has claimed the top records both nationally and even internationally.
LASEK and Epi-Lasik
These two methods are similar to PRK and are only slightly different with each other. In Lasek, the corneal epithelium is removed with the help of diluted alcohol, and in Epi-Lasik, this is performed with a device which is similar to microkeratome. The difference between these two methods and PRK is that the epithelium is embedded back in its place in this method. However, in PRK the epithelium is removed and is no longer used, where a new layer gradually replaces it. At first, it was believed that Lasek and Epi-Lasik are superior than PRK, but our experience and study revealed the opposite. Based on other studies and over time, it was found that the rate of healing and vision outcomes of these three methods were not significantly different with other. Therefore, we no longer use these two methods and prefer PRK and the more advanced trans-PRK.