Laser technology for clear uncorrected vision has existed for about 30 years, and often leads people to LASIK and PRK, which are by far the two most common procedures for vision correction. In some cases, an additional laser “enhancement” procedure may be needed to fine tune the results. The method of the enhancement can be either by lifting the flap, or by PRK which leaves the flap in place. My reasoning behind which of these to do is presented in this blog post which draws on my extensive experience performing laser vision correction surgery.
I have been performing LASIK eye surgery since 1998 and have performed close to 100,000 LASIK and PRK surgeries since then. I had LASIK on my own very nearsighted eyes in 1998. I’ve performed PRK on my mom, my wife, LASIK on my daughter, and placed the EVO ICL in my son. Over the years, my colleagues and I noticed several trends and have modified our recommendations to try to make outcomes better and safer.
Before we get too far into this discussion, let me define some terms:
LASIK Enhancement Flap Lift:
- Understanding LASIK: LASIK involves creating a corneal flap with a femtosecond laser and reshaping the underlying tissue with a different laser called an excimer laser. One of the greatest benefits of LASIK is the rapid recovery and minimal discomfort. However, in about 1-2% of patients, slight residual nearsightedness or astigmatism can be eliminated with a small amount of additional laser. This is commonly called an enhancement.
- LASIK Enhancement Flap Lift: In this procedure, the surgeon uses a fine instrument and lifts the existing flap for further laser correction. It’s my preferred choice in the first 3-6 months after the primary procedure for residual nearsightedness or astigmatism. The recovery time is shorter compared to PRK.
- Candidates for LASIK Enhancement Flap Lift: Patients who had the LASIK procedure within the past year, at the surgeon’s discretion based on the corneal appearance, the laser used for creating the flap, flap size and location, and corneal thickness; a stable prescription for at least three months, which is virtually always the case three months postoperatively and healthy corneas without excessive scarring.
PRK (Photorefractive Keratectomy):
- Understanding PRK: PRK involves removing the outermost layer of the cornea (epithelium) before reshaping it with a laser. It’s suitable for individuals with thinner corneas, when the patient prefers it, for certain vocations (martial arts, military special forces) or those with very deep-set eyes, very small space between their eyelids. or those not eligible for LASIK for some other reason. The procedure is easier to do because there’s no flap, but there’s a longer recovery and about 48 hours of discomfort compared to about 4 or five hours of discomfort with LASIK.
- PRK as an Enhancement: PRK can also be used for enhancement if LASIK is not an option. Since there’s no flap lift, there’s no risk of flap-related complications. PRK enhancement results in a longer recovery compared to LASIK enhancement. There is more discomfort for the first 48 hours, and you will need 5-7 days off work to regain “functional” vision. Your vision will continue to improve for 4-6 weeks or more.
- Candidates for PRK Enhancement: Individuals with thin or irregular corneas. Those not suitable for LASIK enhancement for any reason. The reasons for this often are the fact that there is a complication called epithelial ingrowth that occurs when the protective layer of corneal epithelium can migrate under the flap in the first 2-3 weeks after the procedure.
Comparing LASIK Enhancement Flap Lift and PRK:
SAFETY & RISKS:
- LASIK enhancement flap lift has an easier recovery compared to PRK.
- PRK carries a reduced risk of flap-related complications such as epithelial ingrowth.
- LASIK enhancement typically offers a quicker initial recovery.
- PRK recovery can take longer, but the incidence of epithelial ingrowth is zero.
- Both procedures can provide excellent long-term vision correction.
- The choice may depend on individual factors like the flap appearance, location, scarring, epithelial adherence, and patient age.
CONSULTATION WITH AN EYE SPECIALIST:
- A thorough consultation with an ophthalmologist is crucial to determine the best option.
When we first started doing LASIK, we realized that we could lift the LASIK flap and apply more laser to refine the results if there was any residual nearsightedness or astigmatism. This occurs about 2% of the time, but is more likely in very highly nearsighted (over -6.00) people, and those over 40 years old. After a few years of performing LASIK, we noticed that even though we could lift the flap for an enhancement, we perhaps should not lift the flap if the LASIK had been performed in the distant past.
The reason I, along with a lot of my colleagues decided that we should do PRK for patients who needed an enhancement more than one year after the initial procedure was due to a complication called epithelial ingrowth. Epithelial ingrowth is when the epithelium, the 5 to 7 cell layer thick skin layer that covers the collagen layer of the cornea grows under the LASIK flap. It’s been my observation that the period of about 2 to 3 weeks after the LASIK flap has been lifted is the risk period. If the LASIK flap is clear at the end of 2 to 3 weeks, everything will be fine. If the epithelium has grown under the flap in that 2 to 3 week period, it typically stays about the same. The epithelial growth cycle is about two weeks. After two weeks, the epithelium dies and new epithelium grows. This is a normal protective function of the epithelium-it grows wherever it can. Just like the skin on the rest of our body, it’s constantly shedding and growing new layers from the bottom up.
A factor that has decreased the risk of epithelial ingrowth is our modern Ziemer Z8 femtosecond laser that cuts vertical side cuts rather than planar cuts. To illustrate this, think of yourself as epithelium. The Ziemer Z8 is like getting out of a swimming pool- you have to go up the side and then out. The older lasers were like getting out of the ocean where you gradually move forward out of the water. The edge of the flap now has a steep side cut that makes it more difficult for the epithelium to get in.
Keep in mind that epithelial ingrowth is a very unusual complication and managing it is a significant challenge, so it’s best to avoid it rather than try to fix it once it happens. Many years ago, we just lifted the flap and removed the epithelial ingrowth, hoping it would not come back, but it virtually always did. I have tried various techniques over the years including gluing down the flap with a couple different kinds of tissue glues, using a YAG laser on the epithelial ingrowth- which can occasionally be successful- and suturing with very fine corneal sutures- which seems to be the best defense against recurrence but is tedious and difficult for the patient.
Occasionally I remove the flap entirely and let it heal, which is similar to PRK in terms of the recovery. Obviously, none of these options are ideal. They require multiple patient visits, patient discomfort, and potential for sub-optimal vision results. For this reason, doing PRK when there is increased risk factors for epithelial ingrowth, in my opinion, is absolutely the right decision.
Generally speaking, when a patient is young, had fairly recent LASIK, and has a well-centered and larger LASIK flap, they are the best candidate for a flap lift rather than PRK when an enhancement is needed. Sometimes the epithelium will grow a millimeter or less and causes no problems. If that is the case, of course we leave it alone. The indications for removing the epithelium would be any induced astigmatism or foreign body sensation (which is rare).
Epithelial ingrowth does not occur in the initial procedure, only in an enhancement procedure, and even with enhancement, it is less than one percent or less of all the patients. In my practice, epithelial ingrowth has been virtually zero over the past several years because of our newest technology femtosecond laser and doing PRK on the majority of patients who need an enhancement.
Risk factors for epithelial ingrowth:
The risk factors for epithelial ingrowth are:
- a smaller LASIK flap.
- significant scarring around the edge of the flap, which indicates it is irregular and therefore more likely to provide the pathway for epithelial ingrowth.
- a de-centered flap in which case any epithelial in growth can be visually significant.
- age greater than 45- as we get older the epithelium is more fragile and looser, so it’s more likely to grow under the flap.
Due to the hardship of managing epithelial ingrowth, I prefer to do PRK for enhancements when any of the above risk factors are present.
LASIK enhancement flap lift and PRK are both valuable options for refining vision correction. The choice between the two depends your individual circumstances and consultation with an eye specialist. Regardless of the procedure chosen, laser eye surgery can significantly improve one’s quality of life by providing clear vision!