Although LASIK has become the preferred technique for correcting refractive error, the relative newness of the procedure has spawned a variety of techniques and instrumentation. The confusion surrounding this bewildering array of methods has led many LASIK surgeons to fear potentially troublesome and devastating complications. Universal acceptance of the techniques of LASIK has been stalled by the science's failure to support one approach over another. Unfortunately, this has not escaped the attention of the media or the public, and as a result, LASIK has lost some of its luster. The reality is that LASIK works. Its accuracy, reproducibility, and rapid visual recovery still support its acceptance as a present-day, state-of-the-art procedure. Nevertheless, questions and controversy persist. Which excimer laser is best? Which microkeratome should a surgeon use? Should a different microkeratome be selected for hyperopic treatments than for myopic? Should the flap have a nasal hinge or a superior hinge? Should the flap be kept dry, or should it be wet? These and many other questions continue to plague refractive surgeons.
Surgeons can sort through the perplexing variety of techniques and instruments to adopt a methodical, planned approach to LASIK surgery that works consistently to assure a reproducible, precise, and successful procedure. For several years, I have had success with a simple method of flap construction and management. I first developed the technique for the automated lamellar keratoplasty procedure, and I have since modified it to fit the application of LASIK. In several thousand procedures spanning 7 years, this method has shown itself to be simple to adapt and apply. In my study, conducted in 1999 and reported at the ASCRS meeting, I set out to determine the etiology of DLK. I conducted a prospective evaluation of 682 eyes that underwent LASIK, and discovered that Palmolive detergent and UV light increased the incidence of this feared complication. Inadvertently, I also found that dry sterilization, careful flap handling, and copious chilled irrigation of the flap and bed decreased the incidence of corneal abrasions, flap striae, and keratitis. When it comes to LASIK, I have found that “wetter is better,” and I have coined the name, HydroLASIK, for the procedure that I employ.
THE PROCESS
This procedure features only a few steps and instruments, and the maneuvers it employs are not complicated. The surgeon covers the patient's forehead with a single, clear, adhesive drape, and covers the lower eyelid with clear tape. After prepping the eye with a wipe (betadine), the surgeon applies topical 4% povidine-iodine drops. Anesthesia is achieved with a few drops of topical proparacaine. The instruments are dry sterilized for each case. An aspiration speculum is inserted to keep secretions, tears, and irrigation fluid off of the flap bed. The surgeon reviews the patient's treatment, and a last check of the data entry into the laser computer is verified. The keratome is then selected and positioned over the cornea. For the majority of LASIK procedures, I use a 180- to 200-µm thick flap for an 8.5-mm overall flap diameter. For hyperopic ablations, I prefer a 9.5-mm overall diameter, and I mark the edge of the flap using a dry figure eight marker without ink. My studies have shown ink to be toxic to the epithelium and the stroma, and occasionally, it can find its way into the interface, so I strongly advise against using it. Several drops of sterile balanced salt solution (BSS) are placed onto the cornea beneath the microkeratome, prior to initiating the cut. I inform the patient of what to expect, then verify the position of the ring, and complete the cut.
FLAP CONSTRUCTION
The keys to successful flap construction are proper and consistent suction, smooth excursion of the microkeratome head, and minimal surface friction. Although the controversy concerning flap thickness has not yet been resolved, my experience has shown that excessively thin flaps (thinner than 120 µm) are more likely to be associated with flap problems. If I cannot achieve the full ablation depth and leave at least 300 µm of untouched corneal tissue in the bed (or 60% of corneal thickness), then I will either reduce the ablation, or suggest that the patient considers an alternative treatment such as a phakic refractive lens. Next, I create the flap, and use the pachymetry measurements of the flap and bed to confirm the actual thickness.
FLAP MANAGEMENT
When managing the flap, it is vital to avoid grasping or handling the flap or exposing the flap bed to potential contaminants. It may be tempting to use either a forceps or a hook to lift or grab the flap and to casually fold it over and position it for the laser application. However, flap handling results in predispositions to abrasions, epithelial ingrowth, striae, and keratitis. Forceps that are used to grab or pinch the flap can damage the edge of the flap or disrupt the epithelium, which may predispose the flap to epithelial ingrowth. To steer clear of complications, surgeons also need to avoid touching the undersurface of the flap with anything other than sterile BSS.
To minimize flap handling, I have developed a specially designed flap forceps (Kershner LASIK Flap Forceps; Rhein Medical, Tampa, FL, product #8-16161). Its curved blades act like a thin spatula to slide under the flap edge, rather than pinching or grabbing it (Figure 1). They can lift the flap, flip it over in one maneuver, and reposition it into its original configuration after the laser application. The blades closely follow the contour of the cornea, and when closed, can be used to squeegee the flap to remove residual liquid in the interface. The forceps also can atraumatically relift a flap for retreatment.
I gently lift the flap and position it (Figure 2) without pinching or grabbing the edge. I then align the laser and apply the treatment. At this stage, many surgeons simply flip the flap back and quit. Alternatively, they might manipulate the flap while irrigating underneath it as they change its position. I advise against both approaches. Repositioning the flap is of paramount importance to the success of LASIK. It is mandatory that surgeons reposition the flap in its exact original location, that its surface is smooth, free of contaminants and foreign material, and that it is in the optimum state to reattach to the now-altered underlying stroma. To reposition the flap dry is not sensible, as potential contaminants, debris, and foreign bodies can adhere to the underside of a dry flap. As it falls to the bed, the flap can stick anywhere—not necessarily where it should rest—and entrap unwanted particles.
IRRIGATE FOR FLAP ADHERENCE
A dry flap, when repositioned, can inadvertently create a kink or striae. Consequently, I strongly believe that the bed as well as the underside of the flap should be copiously irrigated with sterile, chilled BSS (Figure 3). Chilled irrigation cools the ablated tissue, minimizes swelling, and allows the flap to float into the proper position. I simply use a liter bottle of refrigerated irrigation fluid, which is hung on an IV pole and connected to tubing with a sterile cannula on the end. When called for, the assistant opens the stopcock and the surgeon directs the stream of water onto the underside of the flap and into the flap bed. The aspirating speculum removes the excess fluid and dries the cornea as irrigation continues. I then use the one-step forceps to reposition the flap, align the edges, and verify that the marks are in the proper alignment (Figure 4). Any excess fluid can be squeegeed with the closed forceps. A dry cellulose sponge can be used to dry and verify that the edges of the flap and gutter are in correct alignment.
LASIK surgeons are well aware of the propensity of the flap to quickly adhere without the need for a patch or sutures. Why does this occur? Normally, the corneal endothelium is responsible for pumping water out of the corneal stroma and into the anterior chamber to maintain the turgidity and clarity of the cornea. This vacuum pump from the epithelium toward the endothelium is very strong.1 This negative pressure creates an adherence and compression of the corneal stroma. When the superficial LASIK flap is created, there is a strong tendency for the flap to adhere due to this negative pressure gradient. That is why in my clinical experience, even after cutting the flap free from the underlying stroma, the surgeon must still physically peel the flap off of the cornea. The flap remains strongly engaged.
After the application of the laser, the surface contour has been altered, but the vacuum pump from the endothelium is still functioning. Ensuring the strongest attraction of the flap to the stromal bed requires water molecules to travel through the stroma to create the negative pressure gradient. If the flap is repositioned dry, the pump has to work that much harder, and the suction is easily broken (in my observations). To create the highest level of vacuum pressure, the endothelial pump must be primed with water to start the pumping of fluid through the stroma and into the anterior chamber. Contrary to conventional thinking, irrigation actually makes the flap adhere better. Just as the corneal incision for cataract surgery seals by pumping the hydrating fluid out of the cornea, the natural physiology of the cornea makes flap adherence possible.
KEEP THE EYE DRY AFTER LASIK
The patient should not instill eye drops the day of the procedure, as until the epithelial edge is sealed intact, eye drops promote swelling of the cornea and decrease the likelihood of flap adherence. The postoperative LASIK patient should rest with the eyelids closed for several hours to allow deturgescence to occur. On the following day, the application of a topical antibiotic/anti-inflammatory eye drop four times per day for 1 week can commence. Artificial tear supplements are strongly encouraged, as all LASIK patients will experience symptoms of dry eye for at least several weeks following the procedure. To protect the patient from the potential keratitis that can occur with exposure to the sun, ultraviolet-blocking sunglasses are provided for all patients.
CONCLUSION
By using water as an adjunct tool in LASIK, the flap can be carefully positioned without the need to grasp or hold it. This prevents the problems inherent in any forceps or cannula manipulation. Corneal abrasions, pinches, and kinks in the flap can all be avoided if the only thing that touches the flap is water. When combined with the one-step flap forceps, HydroLASIK can increase the likelihood of satisfactory flap repositioning without the need for multiple instruments or adopting difficult maneuvers. In my experience, the potential risks of epithelial ingrowth, striae, and keratitis decrease with a wet technique. With today's LASIK procedure, water is truly our friend—“wetter is better.”
1. Duane and Jaeger: Duane's Biomedical Foundations of Ophthalmology (vol 2, chap 4). Harper and Row, Philadelphia, PA, 1983
