Staphylococcus aureus the most common infection after LASIK

Infections after LASIK can cause severe problems for patients and can be difficult to diagnose, according to Francis Mah, MD, from the University of Pittsburgh, PA, United States.

Dr. Mah recounted a typical case of a 65-year-old healthy patient with low preoperative sphere who underwent uncomplicated bilateral LASIK and rapidly developed substantial pain, focal infiltrates, diffuse lamellar keratitis, and melting of the flap edge in one eye 1 day after surgery. Following irrigation with vancomycin (Vancocin, AstraZeneca) and flap amputation, the patient's vision was 20/40 with a hard contact lens in the affected eye.

The differential diagnosis included atypical bacterial infection and necrotising keratitis, which were ruled out because of the speed with which the infection developed. The patient had developed methacillin-resistant Staphylococcus aureus, which is actually becoming the most common cause of infection after LASIK, Dr. Mah said. He speculated that the source of the infection was the patient's wife who had had an infection before the surgery.

Dr. Mah pointed out that there has been a shift to S. aureus infections, which now constitute 61% of all infections after LASIK. Streptococcus and gram-negative infections now account for 12% each and mycobacterium only 5%. He speculated that the new fourth-generation fluoroquinolones may be preventing mycobacterial infections.

Dr. Mah typically administers a drop of moxifloxacin (Vigamox, Alcon Laboratories), a fourth-generation fluoroquinolone, and a nonsteroidal drug 30 minutes before LASIK. Postoperatively, he instructs patients to apply the drugs every 1 to 2 hours on the first day after LASIK, after which the drugs are applied three times daily for 1 week.

"No studies have been done to identify the best time point for applying antibiotics," Dr. Mah said, while commenting on the use of antibiotics a day or two before surgery. However, he noted, that the fourth-generation fluoroquinolones kill within an hour of application, significant concentrations are achieved rapidly within 15 minutes, and patient compliance may be problematic when drugs are prescribed in the days before surgery.