Excimer laser refractive surgery, and LASIK in particular, is the most popular refractive procedure worldwide. However, alternate procedures are available for favorably modifying the refractive properties of the eye, and when laser vision correction is not appropriate, these procedures become valuable tools for the refractive surgeon. This chapter is an introduction to help the reader understand the role that these alternatives can play in helping the patient achieve better uncorrected vision.

The various names for keratorefractive surface ablation with the excimer laser are derived from the technique used to handle the epithelial layer. The first FDA-approved refractive surgery procedure using the excimer laser was photorefractive keratectomy (PRK). This procedure involves the mechanical removal of the epithelium followed by excimer ablation of the underlying surface stroma. Although the mechanical removal was initially done with a blade, a battery-operated rotating brush was developed to facilitate epithelial removal (See Video 5). Later, the use of dilute ethanol (20%), or isopropyl alcohol (35% to 70%) was introduced to facilitate mechanical epithelial removal. The alcohol pretreatment effectively loosens the adhesion of the basal epithelial cells so the layer can be gently swept aside. An alternate technique uses the excimer laser to partially remove the epithelium prior to the refractive ablation. This requires the mechanical removal of the remaining epithelium from the ablation zone and was, therefore, termed laser-scrape.

Surface ablation, in the early years of laser vision correction, was performed with broadbeam lasers and lacked the more recent advances of medications to control postsurgical discomfort, and medications like mitomycin-C to reduce the potential for stromal haze with deeper ablations. That led many surgeons to rename the procedure advanced surface ablation (ASA) to differentiate the more modern technique.

With any technique that involves the removal of the epithelium, there is associated postoperative discomfort and delay of vision recovery until the epithelial layer is healed and optically smooth. In the hopes that preserving the epithelium and returning it to the surface following the laser ablation would minimize the soreness and hasten the visual recovery, techniques were developed that allowed the epithelial surface to be lifted as a sheet and then replaced over the treated surface. When this is performed with chemical loosening of the epithelium and mechanical lifting of the flap, it is called LASEK (laser-assisted subepithelial keratectomy). When it is performed using an epithelial keratome, it is known as Epi-LASIK. The epithelial keratome uses an oscillating blunt dissector to separate the sheet of epithelium from Bowman layer. The advantage of retaining the epithelial flap for either pain control or more rapid visual rehabilitation has been difficult to scientifically establish, and it is no longer a popular common practice.

Several advantages make surface ablation an important alternative to LASIK. The longterm postoperative results of surface ablation surgery are comparable to those of LASIK, particularly for myopic corrections of ≤ —5.00 diopters (D). Because no stromal flap is created, risks such as striae, flap displacement, loss of suction during flap creation, diffuse lamellar keratitis (DLK), and epithelial ingrowth are eliminated. This is also true of the risk of flap segmentation or wound disruption problems, which can occur after LASIK in post-radial keratotomy or penetrating keratoplasty patients.

Laser refractive surgery is increasingly being performed to modify the refractive results from lens implantation. As premium lens implantation becomes more popular, patients’ expectations for perfect refractive results necessitate that surgeons have the capability to use the excimer laser to correct astigmatism or unintended spherical refractive error. Surface ablation avoids concern that the microkeratome or femtosecond laser could disturb the cataract incision or limbal relaxing incision during flap creation.

An important advantage of PRK is that more stromal tissue is available for safe laser ablation. If a typical LASIK flap measures 100 to 160 µm in thickness including the 50- to 60-µm epithelial layer, a surface procedure can be performed with an additional 40 to 100 µm of stromal tissue available for ablation. This is particularly helpful in treating patients with relatively thin corneas or patients with higher myopic refractive errors. Because customized wavefront-based LASIK surgery requires the ablation of more stromal tissue, surface ablation may be needed in order to leave sufficient residual stromal bed thickness.

Less severe and less prolonged dry eye problems are encountered after surface treatment, which is advantageous in patients who have preexisting tear film problems. When there is no suction ring to raise the intraocular pressure, there is less concern for ischemic complications to the optic nerve, and this may be more suitable for patients with risk factors for glaucoma or other optic nerve diseases. A suction ring cannot be used on a patient with a filtering bleb, while surface ablation might be safely performed in this circumstance.

The cost per case is considerably lower for surface ablation procedures than for LASIK performed with either the microkeratome or femtosecond laser.

The three major disadvantages of surface ablation are postoperative discomfort, slow visual rehabilitation, and the risk of stromal scarring. The removal of surface epithelium by any technique is associated with postoperative pain. This can range from mild to severe and may last for several days until the epithelium has healed. Pain can be minimized with bandage contact lenses topical cycloplegics, oral analgesics, cold compresses, oral and topical nonsteroidal anti-inflammatory medications, and even dilute topical anesthetics. Immediately following surface ablation, the vision can be quite good with uncorrected visual acuity (UCVA) in the range of 20/30 to 20/60. As the epithelium heals during the next few days and the central optical zone becomes rough and irregular, the vision becomes hazier. The initial epithelial layer is somewhat thickened, but gradually smooths out to achieve better optical quality in the subsequent weeks after surgery. The UCVA after the first week is typically 20/30 to 20/40 and may take a few weeks to achieve 20/20 or better visual acuity. Retreatment should not be considered for 6 months after PRK, because of the time necessary for complete healing and refractive stability to occur.

Stromal scarring in the form of reticular haze occurs with increasing frequency and severity with myopic corrections above —5.00 D and ≥75-µm ablation depth, and was generally more common with broad-beam laser procedures. It is less frequent with modern spot lasers but can still occur with higher corrections. The haze usually peaks between 1 and 3 months. Several measures can minimize the incidence and severity of this scarring even at higher corrections. These include intraoperative application of topical mitomycin-C after ablation, lowering the cornea temperature with chilled balanced salt solution (BSS) after the ablation, the use of oral ascorbic acid (1,000 mg daily), reducing sunlight exposure after surgery, and the use of a topical steroid for at least a month following surgery. Prolonged topical steroid use should be monitored as it
increases the risk of IOP elevation that can become quite severe. Of the various modalities used to prevent postoperative haze the use of mitomycin-C, 0.2 mg/cc is most effective and has become routine for many surgeons performing surface ablation procedures (see Chapter 13 for a more detailed discussion). Enhancements after surface surgery require the patient to go through the same process with discomfort and slow return of useful vision. During the enhancement procedure, the surgeon should be prepared for greater epithelial adhesion and a rougher appearance of the stroma within the previous ablation zone.

The technique for ASA involves loosening the epithelial cells with alcohol solution applied to the corneal surface within a circular well of the desired diameter or by placing a round cellulose sponge dampened with the solution on the surface (See Videos 6-9). The time of contact with the alcohol varies from 15 to 45 seconds depending on the alcohol concentration used, and the condition of the epithelium. Longer contact time may be required to loosen epithelium for enhancement of a previous surface ablation. Limiting the duration of alcohol contact with the epithelium, removing the alcohol, and copiously irrigating the corneal surface with BSS will minimize stromal penetration and possible toxicity. If a rotating epithelial brush is used (See Video 5), the alcohol solution is not required. If an epithelial flap is to be prepared, the edges are bluntly dissected centrally to create an intact epithelial layer that is reflected away from the treatment zone. The laser ablation is performed. For procedures with ablation depths >75 µm, mitomycin-C 0.2 mg/cc on a cellulose sponge can then be applied to the stromal surface for 12 to 30 seconds. The surface is irrigated again with chilled BSS. A bandage contact lens is placed on the cornea and the procedure is complete.

Various oral analgesics (e.g., celecoxib, gabapentin, and pregabalin) are commonly prescribed for use beginning the day prior to surgery and continuing for 1 to 2 days after surgery to help minimize discomfort. Cold compresses can be used as well. Oral ascorbic acid 1,000 mg/day, if used, is begun the day of surgery and is continued for 1 month. Topical antibiotic and steroid eye drops are used four times daily. The antibiotic can be discontinued once the epithelium is healed, but the steroid is continued for at least 1 month. The bandage contact lens is removed when the epithelium is intact, usually on the fourth postoperative day.

Bilateral simultaneous surgery is commonly performed, but the patient must be thoroughly prepared preoperatively for the visual disability that will likely occur during the first week after surgery. Many patients will, therefore, opt for sequential surgery, which is less convenient but reduces the transient visual disability that occurs during the first postoperative week.

The use of heat to change the shape of the cornea is more than 100 years old, but only recent advances in technology have allowed the controlled application of heat to predictably change the corneal shape without causing necrosis and scarring. The goal is to apply heat to the mid-peripheral cornea to induce shrinking, which secondarily steepens the central cornea, correcting hyperopia.