The technique of superficial keratectomy with MMC for existing corneal haze is described in this section. It is important to note that MMC in no way eradicates corneal haze; rather, MMC prevents the stromal keratocytes from depositing additional scar. Therefore, it is imperative that the scar be completely removed. Two methods are used to remove scar tissue: mechanical debridement using a 64 Beaver blade or a diamond-dusted burr, like that used for pterygium removal and excimer laser phototherapeutic keratectomy (PTK). Both methods may work equally well. In either case, multiple intraoperative slit-lamp examinations may be required in order to gauge the efficacy and determine the end point of the keratectomy. When using PTK, care must be taken to vary the distribution of pulses throughout the corneal surface in order to reduce the likelihood of unwanted hyperopic shifts.

Once the scar has been removed, it is of the utmost importance to follow the protocol for MMC application meticulously in order to prevent potential complications. This begins with procurement of the medication. Significant deviation from the concentration and duration of exposure can lead to vision-threatening adverse events. Our protocol is to have MMC 0.2 mg/mL (0.02%) prepared by an independent compounding pharmacy in order to minimize errors in dilution. A common area of confusion is the unit of measure for the MMC; 0.02% is equivalent to 0.2 mg/mL, but there have been anecdotal case reports of 0.2% being used. This is 10 times the suggested concentration and results in severe endothelial toxicity.

Once the MMC has been correctly prepared, 1-mL aliquots may be frozen for several weeks until ready for use. The MMC is thawed prior to surgery and placed in an empty disposable contact lens well. Proper application of MMC to the corneal surface is best achieved by using a 6- to 8-mm circular Merocel sponge (Beaver-Visitec International, Inc., Waltham, MA), commonly used in the operating room to shield the retina from microscope-induced phototoxicity. The advantage of the corneal light shield over a spear is that the light shield achieves better contact with the corneal surface and, more importantly, prevents excess MMC from coming into contact with the limbus. Limiting the spread of MMC is critical in reducing potential postoperative complications. The corneal light shield is placed in the MMC solution at the beginning of the case and is left in the solution until needed.

During application of MMC, care should be taken to ensure that the shield is wet but not dripping with MMC. It is placed on the central cornea, and the surgeon must meticulously monitor the surface to prevent MMC from coming into contact with the limbus and conjunctiva. The duration of exposure is exactly 2 minutes. After the allotted exposure time, the MMC-soaked sponge is carefully removed and discarded, a cellulose sponge is used to remove any excess MMC left on the cornea, and the surface of the eye is vigorously irrigated with 30 mL of balanced salt solution. These steps remove excess MMC from the corneal stroma, and will also help to minimize potential complications.

Typical post-keratorefractive surgery medications are administered—topical antibiotics, corticosteroids, and nonsteroidal anti-inflammatory agents—and a therapeutic bandage contact lens is placed. The cornea is carefully
monitored for reepithelialization, which typically occurs in 3 to 5 days. The patient should be forewarned that visual recovery may be slow, and that the final refractive error is difficult to predict. The possibility of the future need for refractive treatment should be explained.