Resources:LASIK vs PRK


Procedure Types

Your laser treatment, whether Wavefront Optimized or Topography Guided Contoura, can be delivered in a number of ways that differ primarily on the layer of the cornea that is treated and how that layer is exposed.

The LASIK Procedure

In the United States, the LASIK procedure has traditionally accounted for approximately 90% of all laser refractive procedures, with its alternative, PRK, accounting for the remaining 10%. In the 1990's and the early 2000's, a bladed microkeratome was used to create a "corneal flap" that includes the epithelium, Bowman's membrane and a portion of the deeper, underlying layer known as the stroma. In June of 2004 Hale Vision introduced the Intralase bladeless flap creation technology to the Southeastern Wisconsin area. This technique has been referred to as "All-Laser LASIK" and then as "iLASIK" when used in combination with the Custom WaveFront Guided treatments of the Visx S4 IR excimer laser. The "iLASIK" procedure is what was often referred to when the discussion of LASIK for NASA astronauts and military pilots are mentioned, as that is their original treatment of choice. Following the creation of the corneal flap, a laser treatment is then applied to the exposed corneal stroma. Afterwards, the flap is repositioned over the treated surface. Because the surface epithelium is relatively undisturbed, LASIK is the most comfortable laser procedure and offers the most rapid healing. As the years progressed, the laser technology improved, and TLC Milwaukee/Hale Vision now uses what we feel to be the current state-of-the-art technology the Wavelight FS200/EX500 CONTOURA capable system.

The PRK Procedure

Unlike LASIK, with PRK, no flap is created. Instead, the epithelial cells over the treatment area are loosened and removed, and the laser treatment is performed directly on Bowman's membrane. In the Epi-LASEK variant of the PRK procedure, an attempt is made to put the epithelial cells back into place after the laser treatment, but with standard PRK, no such attempt is made, and the epithelium heals when new cells grow in from the periphery. Studies have shown no significant advantage in the Epi-Lasek procedure over standard PRK therefore, this is not a procedure we offer at TLC Milwaukee/Hale Vision.

Because the surface epithelium is disturbed, PRK is less comfortable than LASIK and the eye heals more slowly. After PRK, you will need to wear a soft bandage contact lens for three to five days, until the epithelium is completely healed. This is to protect the cornea as it heals, as well as to keep the eye more comfortable. Your vision will improve daily, but it can take as much as a week for it to return to a functional level, and several weeks or months for it to reach its final clarity. Retreatments, which less frequent than with Lasik, are also delayed for up to a year as the eye can continue to slowly improve over a longer period of time than seen with the Lasik procedure. Medicated drops may be used for several months with PRK compared to the typical one week with Lasik. Both the PRK and Lasik procedures require the use of lubricating drops postoperatively.

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 capable of driving to their postoperative day one visit with clear, comfortable vision (although they are advised to utilize a driver as lingering medication effects or mild light sensitivity could make it unwise). Medicated eye drops are used during the initial seven 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: While the need for retreatment procedures has become far less common with advances in technology, 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 an unusual 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.

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. In cases of larger refractive treatments with PRK a medication known as Mitomycin C is applied during the procedure to reduce the risk of haze formation.

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 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, typically requires the patient to shift to a surface procedure as the second attempt at a blade flap can cause added complications. 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 more than 20 years with the excimer laser combine to produce a safe procedure. PRK also has similar 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 a LASIK retreatment, too. Currently, the procedure of choice for secondary procedures performed beyond one year of an original LASIK is PRK on top of the LASIK flap.

No flap complications: Because no corneal flap is made with the PRK procedure, flap-related complications are non-existent. The use of the femtosecond laser to make the flap has significantly reduced the already tiny incidence of flap creation complications.

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.

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: With the PRK procedure your eye may be very sensitive to light for the first days after surgery. The sensitivity can usually be alleviated with sunglasses. LASIK does not usually cause significant light sensitivity.

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. Although it was common in the past to perform PRK on one eye at a time, modern techniques now allow both eyes to undergon the procedure at the same time, similar to LASIK.

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. PRK is usually associated with the least dryness, All-Laser LASIK perhaps a bit more, and the bladed microkeratome probably the most as it tends to cut deeper and effect more nerves.

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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