Photorefractive Keratectomy (PRK) was the first laser refractive eye surgery that is used to remove (ablate) tissue directly from the eye’s surface to change the curvature of the eye cornea successfully. The surgery is a proven procedure designed to correct nearsightedness, farsightedness, and astigmatism.
Even when the excimer laser was developed in the early 1970s and modified for ophthalmic use in the early 1980s, the Food and Drug Administration did not approve its use for refractive eye surgery until 1995.
Coming before LASIK refractive eye surgery, PRK’s principle of vision correction is pretty much the same and remains to be performed frequently and regularly today. After the reshaping of the cornea, light rays are then allowed to focus properly on the back of the eye, the retina. The procedures, each involving similar tools and length of time with a surgeon, have the same goal but they are different in key ways.
PRK or LASIK Eye Surgery
PRK offers an excellent success rate and an ideal alternative for patients who may not be a good candidate for LASIK eye surgery. Similar to the latter, it is also an outpatient surgery and takes only about five (5) to fifteen (15) minutes to complete in each eye.
With LASIK surgery, a thin flap is created on the cornea. The flap of tissue is lifted and the computer-controlled surgical laser carefully reshapes the layers of the cornea to repair imperfections in curvature that lead to distorted vision. The flap, that is not visible to others, will secure itself back to the eye, however, it will always remain.
LASIK Eye Surgery
On the other hand, PRK offers its own benefits. It does not involve surgical flap complications as it only consists of the mechanical removal of the corneal epithelium (surface cells), that is followed by use of the excimer laser to remove small amounts of tissue from the front of the cornea.
PRK Eye Surgery
The recovery process for each procedure is a bit different as well. The recovery from the PRK eye surgery takes a while longer than that LASIK as the outer layer of the cornea needs ample time to heal. Postoperatively, the PRK patient is then given prescription antibiotic and anti-inflammatory eye drops to allow for a speedy healing process. Also, allow two (2) to three (3) days for possible discomfort and blurring to subside. It takes about six (6) months to attain peak visual acuity.
LASIK recovery is defined faster. Most patients have reported seeing normally in a matter of hours from surgery as their vision improves gradually over the course of several months. Should there be any discomfort, it is mild and usually lasts short term.
Having the right eye surgeon by your side makes a considerable difference in your PRK recovery.
Who is a good candidate to PRK? Should the patient have dry eyes and thin corneas, PRK may a good choice. Competitive athletes or people at risk of eye injury might consider PRK too. The corneal flap resulting from LASIK does not exist, therefore eliminating any risk of damaging it.
Moreover, the eye surgeon performs eye examinations to identify whether one is a good PRK candidate. Usual points to check are refractive errors, cornea and pupil measurements, and overall eye health.
Patients who have any of the following are not candidates to PRK:
- thin corneas
- corneal disease
- glaucoma or cataract (advanced)
- diabetes, pregnant, or nursing
- changing refractive error
What are the differences in costs? Since PRK does not involve the added step of creating a corneal flap, it is simpler and slightly quicker. Therefore, it is cheaper and typically costs less than LASIK.
There is a variation of PRK called LASEK. With LASEK, the surface cells (corneal epithelium) are soaked in a dilute solution of alcohol, pushed aside as a single sheet, and then pushed back over the surface of the cornea after the laser treatment is completed. It is a less popular procedure due to its substantially longer recovery time.
Step-By-Step PRK Treatment
During the procedure, the patient lies comfortably with the laser system on top of the face. Vision correction is done on one eye after the other. The patient may choose to have the correction on the other eye right after the first or on a separate surgery day. Eye drops (anesthetic) are then used to numb the eye. Next, an eye speculum is placed on the eye to keep the eyelids open, which is normally not uncomfortable, while the patient is asked to focus on a target light. The surgeon then proceeds to remove (ablation) the microscopic amounts of tissue from the surface layer of the cornea (corneal epithelium). Either a special brush, blade, laser or alcohol solution is used to do so. The patient will be notified once the excimer laser is ready to work. The ophthalmologist moves to use the laser to apply computer-controlled pulses of light energy, that are programmed with the patient’s exact prescription, to reshape the cornea. With the current laser technology, the laser will follow in case the eye moves and will completely stop if it moves far out. The laser will resume where it left off once the patient has fixed his or her sight back to the target light.
The whole procedure approximately takes five (5) to fifteen (15) minutes to complete in each eye. Some pressure sensation may be felt during the surgery, however, it is generally painless. The epithelial layer grows back over the next 3-4 days. The surgeon inserts a bandage contact lens to protect the cornea as it also helps decrease the discomfort one may experience (generally mild to moderate) during early recovery. The cornea heals from the edges towards the center, forming a “ridge” by the fourth or fifth day. The vision has significantly improved by this time, generally ranging between 20/30 and 20/50. Often, the correction is said to be stable within 3 to 6 months from the date of surgery.
PRK Risks Involved
As per any eye surgery, photorefractive keratectomy (PRK) carries a certain amount of potential risks. One should consider the occurrence of any of the following:
- glares around lights
- corneal haze (clouding of the cornea during the healing process)
- reaction to anesthesia
- undercorrection or overcorrection
- dry eye
- corneal infection
Also, there is the possibility of retreatment, that is requested approximately by ten (10) to twenty (20) percent of patients, due to regression, defined as a gradual partial or complete return to the myopic state. This remains a common complication of the excimer laser with PRK and limits the predictability of refractive outcome, especially in high myopia. A retreatment PRK surgery may significantly reduce residual myopia in the majority of patients and a deliberate overcorrection (50%) may reduce the chance of further regression as well.
While LASIK can be the most popular refractive eye surgery to date, the judgment and guidance of the eye surgeon, together with the patient, can weigh the risks and rewards of PRK.