The Book
Pros/Cons of LASIK & PRK
The Advantages of LASIK
Quick Recovery: LASIK offers the fastest recovery time of all the vision correction procedures, as the protective corneal flap seals within hours and brings an end to the typical scratchiness and irritation after surgery. Most LASIK patients are able to drive to their postoperative day one visit with clear, comfortable vision. Medicated eye drops are used during the initial five days following surgery and are usually not required after that. This rapid recovery is one of the main reasons that the LASIK procedure has become so popular.
Easier Retreatments: The rapid healing of LASIK also comes into play if a retreatment is needed. With PRK retreatments, the entire prolonged postoperative scenario is repeated, while with LASIK, the recuperative period is again quite brief.
Minimal Discomfort: Most LASIK patients describe a pressure sensation during creation of the corneal flap, but few describe it as pain. After LASIK, the typical patient experiences a scratchy sensation that quickly resolves after a few hours. This high comfort level is another one of the main reasons that the LASIK procedure has become so popular.
Both eyes can be treated at once. This is in contrast to the PRK procedure, whereby a minimum of one week is generally required in between eyes, so that both eyes are not blurry at once.
Rare Haze Formation: Since the laser treatment is performed beneath a protective flap, there is typically no surface reaction or haze, as is sometimes seen with PRK.
The Disadvantages of LASIK
More Surgeon Dependent: The added complexity and elegance of LASIK, when compared to PRK, requires more extensive surgeon and staff training. Due to the importance of the LASIK flap, and the potential for flap-related complications, experience becomes a major factor in the outcome of the surgery. The
all-laser LASIK Intralase procedure helps reduce the potential complications and enhances the visual results.
Possible Flap Complications: A well-formed flap is an essential prerequisite for a superior laser treatment. The possibility of an imperfect flap, while relatively rare overall with the handheld bladed microkeratome, required the patient to wait for 3-6 months before being able to attempt repeating the procedure. The
all-laser LASIK procedure has made the possibility of flap complications even more rare, and if there is a problem it can usually be corrected in hours or days, rather than months.
Other potential flap concerns include microscopic, postoperative wrinkles and postoperative inflammation underneath the flap (a.k.a. SOS / DLK).
Eye Trauma Concerns: Despite the fact that LASIK flaps seal quite firmly, there is still a remote possibility that extreme trauma directly to the eye could dislodge the flap. For this reason, individuals with a high likelihood of experiencing a direct blow to the eye, such as police officers and martial arts enthusiasts, may wish to consider a flapless procedure like PRK.
Limited Long Term Studies: Another possible disadvantage of LASIK is the lack of long-term scientific studies, although many doctors feel that the 30-year experience with other flap procedures and 19 years with the excimer laser combine to produce a safe procedure. PRK also has only 19 years of experience, as it, too, is a laser-dependent procedure.
The Advantages of PRK
Preservation of Corneal Thickness: All laser treatments reshape the cornea by removing small amounts of corneal tissue. Consequently, the cornea is simultaneously thinned. The amount of thinning is proportional to the amount of correction needed, and there is a limit to how thin we can make the cornea without affecting its long-term stability.
Because the LASIK flap includes corneal tissue that otherwise would have added to the thickness available for the laser treatment, corneal thickness is more of a concern with LASIK than PRK. In some patients, the cornea is too thin to undergo the flap-dependent LASIK procedure, and PRK is the only feasible alternative. The ALL-LASER LASIK procedure has also increased the number of patients who will be eligible of LASIK as the laser is capable of creating thinner flaps than can the mechanical microkeratome. This saves tissue and allows for a greater treatment range.
If a patient is very young and less likely to have completely stabilized his or her prescription (i.e. more likely to need a retreatment in the future), PRK may allow more potential options, because it preserves more corneal tissue for future treatments. However, in most adults with stable prescriptions and normal thickness corneas, this issue is not a concern, because there is usually plenty of corneal thickness to do another LASIK treatment, too.
No flap complications: Because no corneal flap is made with the PRK procedure, flap-related complications are non-existent.
No eye trauma concerns: Because no corneal flap is made with the PRK procedure, there is no concern that extreme trauma could dislodge a flap.
Lower retreatment rates: Statistically, there is a lower chance of needing a retreatment with PRK, though the difference is small.
The Disadvantages of PRK
Prolonged Recovery Time: Whereas LASIK patients are typically comfortable and see well the day after surgery, PRK patients often experience discomfort for several days and a few weeks are often needed for the vision to recover. As a result, the postoperative follow-up care after PRK is more involved than that of LASIK. More postoperative visits are required and medicated eye drops are used for a longer period of time.
More postoperative discomfort: Discomfort from vision correction procedures occurs when the surface epithelial layer is disturbed. With LASIK, this disturbance is minimal and occurs only at the flap margin. However, with PRK, an entire sheet of the epithelial layer is loosened and removed to expose the underlying cornea for the laser treatment. Discomfort from PRK therefore remains until all areas of this epithelial sheet have healed back in. This process can take several days.
Extended Retreatment Recovery Times: Because the surface epithelium must again be removed, the entire, prolonged recovery time is again experienced with PRK retreatments.
Haze: Natural tears carry cells and other substances that promote inflammation after surgery. With PRK, the treated layer of the cornea is very close to the tear film layer, and as a result, a haze reaction can sometimes develop. With LASIK, the treated layer is protected by the corneal flap, so haze is not a concern.
Another factor that influences the likelihood of haze formation is the preoperative severity of the correction undertaken, as higher levels of correction are more likely to develop haze.
Mild haze is generally not a problem and resolves with time. On rare occasions, however, haze can be quite stubborn and take months of therapy with steroid eye drops or the surgical application of a medication known as MMC to resolve.
Infection: Although extremely uncommon, infection is slightly more likely after PRK than LASIK.
General Healing Concerns of LASIK and PRK
Pain: Though the discomfort associated with PRK is usually alleviated with medications, and lessens significantly as the surface regenerates, occasionally the going is a bit rough for a few days. Little to no pain is the usual experience with LASIK.
Light Sensitivity: Your eye may be very sensitive to light for one or two weeks after surgery. The sensitivity can usually be alleviated with sunglasses.
Eye Coordination: If both eyes need correction and only one is operated on initially, there may be a problem with coordination between the corrected and the uncorrected eye. This can be pronounced in glasses but usually reduced with a contact lens in the unoperated eye. Occult muscle imbalances may rarely be uncovered by laser surgery and could require further treatment including muscle surgery.
Initial Overcorrection: Most laser programs overcorrect the eye initially to compensate for the eye's natural healing process. This overcorrection may cause temporary symptoms of farsightedness. Most eyes will stabilize within a few weeks or months.
Night Vision: Remember to check your night vision status before surgery, as most patients have some night vision disturbances preoperatively. Some patients will experience a temporary halo effect around bright lights after surgery. With modern lasers, this usually lasts for several weeks and clears by three months. However, a small possibility exists that this effect could last much longer or be permanent. Preoperative care in patient selection is key to reducing this possibility.
Dry Eye: Many patients seeking vision correction surgery do so because they have developed dry eyes and subsequent intolerance to contact lenses. However, all corneal laser treatments cause eye dryness to worsen, because they temporarily damage the surface nerves of the cornea that are responsible for reflex tear secretion. These nerves can take as long as a year to heal.
Most patients regain adequate tear function within two or three months, but it is essential to use artificial tears until this occurs. The first two weeks postoperatively are the most important for all laser procedures and tears should be instilled every hour or two while awake.
Possible complications of LASIK and PRK
While serious complications are very rare, it is important to realize that there may be adverse side effects from these procedures. Anyone who is considering laser vision correction should be aware of the following possible complications.
Overcorrection: While most of us respond to laser treatments in a similar fashion, there are always exceptions. Over the years, most surgeons have developed sophisticated means for adjusting their laser treatments in order to reduce treatment surprises, but they still occur. In younger patients with mild overcorrections, the eye may adjust enough to overcome the situation. However, in older patients or larger overcorrections, glasses, contacts or laser retreatment may be necessary.
Undercorrection: If the planned laser treatment does not achieve the targeted amount, it is usually correctable with a laser retreatment. If this necessary, it is usually performed between three and six months after the original surgery. If additional surgery is medically unwise, glasses or contact lenses may be necessary.
Delayed Epithelial Healing: The epithelium is a thin protective layer of cells that covers the cornea and is removed during PRK. The epithelium usually grows back in a few days. Most PRK patients experience discomfort until the epithelium has healed. Special treatment may be needed if the epithelium does not heal in the normal amount of time. Epithelial healing is rarely an issue with LASIK.
Reduction of Best Corrected Visual Acuity: Modern lasers offer improved beam patterns and smoothness, along with enlarged treatment zones and eye trackers. These factors reduce the incidence of irregularities in the final corneal surface and improve the quality of vision. Unfortunately, it is still possible for an individual cornea to absorb the laser pulses in an uneven manner causing a less than ideal shape. If mild, this causes little to no problem, but if excessive, it can cause distortion and a reduced quality of vision. The incidence of this was only 0.5% with the older generation lasers and has improved with the newer models, but is still not zero. Please check with us for the latest information and statistics. Different solutions are usually available for these situations, including specialized laser treatments and contact lenses.
De-Centration of Laser Treatment: It is possible, but unlikely, that a misalignment of the patient and the laser beam could occur during surgery. The new eye tracking systems help reduce this possibility, but the surgeon must still be vigilant and the patient cooperative.
Our doctors are among a small minority that are certified in the VISX C-CAP program to attempt repairs of these situations.
Inflammation (DLK, SOS): Diffuse Lamellar Keratitis (DLK), which has also been termed "Sands of the Sahara" (SOS), due to its sandy microscopic appearance, refers to inflammation beneath a LASIK flap. DLK is usually mild and easily treated with eye drops. However, if severe and inadequately treated, DLK can rarely affect the visual outcome. Since no flap is created with PRK, DLK is not possible.
Infection: The most serious complication of most eye surgery is that of infection, which is rare with all laser procedures, but slightly more likely with PRK than LASIK. This is due to the temporary alteration in the epithelial layer (inherent to PRK) which normally serves as a barrier against infection. Therefore, until the epithelial layer has healed, there is a slight increase in the possibility of an infection.
Infections are typically minor and treatable with eye drops. The incidence of serious infection has been placed at 1 in 1,000 or more by some authorities.
Flap Complications: Intraoperative flap complications, which are serious enough to abort a planned procedure, occur at varying rates according to different studies. These studies all apply to the handheld, bladed microkeratome. In general, the complication rate decreases as the experience of the surgeon increases. At Hale Vision Laser & Implant Center, our rate of flap complications was very low at 0.18% and in our never-ending desire to make the procedure even safer, we have introduced the new
all-laser LASIK procedure.
Most of the time, when a flap complication occurs, the procedure can be reattempted in 3 months, should the patient wish to do so.
Flap related complications can occur after surgery, too, as inflammation under the flap (SOS / DLK) and small, microscopic wrinkles in the flap are occasionally encountered.
Once again, flaps are only created for the LASIK procedure, not PRK. Individuals who are particularly concerned about flap problems may therefore wish to consider PRK.
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