Mycobacteria, fungi common in post-LASIK microbial keratitis

The prophylactic antibiotics commonly used in LASIK provide no coverage against these microorganisms.

ByMichela Cimberle

BARCELONA – When microbial keratitis is diagnosed after LASIK, the surgeon should be aware that it might be caused by microorganisms normally rare in this disease, such as mycobacteria and fungi.

“The data I found in literature confirmed my experience. About 40% of post-LASIK microbial keratitis are caused by gram-positive cocci, which is what you would expect. However, mycobacteria originate this complication in 30% of cases, and fungi in 15% of cases,” said Juan J. Pérez-Santonja, MD, speaking here at the winter meeting of the European Society of Cataract and Refractive Surgeons.

According to Dr. Pérez-Santonja, these are rare microorganisms in non-LASIK-related microbial keratitis, which means there is something specifically related to the LASIK treatment that is causing the infection.

“When we perform LASIK, we use prophylactic antibiotics such as ofloxacin or ciprofloxcin, which target some specific microorganism more commonly involved in microbial complications. Many microorganisms, more than 95%, are sensitive to ofloxacin. However, some of them escape, and these are mycobacteria and fungi. I think this might be the reason for such a high percentage of microbial keratitis with this unusual origin,” he said.

Targeted diagnosis and treatment

The diagnosis of microbial keratitis is based on some specific signs, Dr. Pérez-Santonja said. Whitish stromal infiltrates are visible in the interface and invade the surrounding stroma. Ciliary or conjunctival hyperemia might be present. Patients report moderate-to-severe pain, photophobia and impaired vision.

“Don’t try empirical use of antibiotics, even if you feel sure of your diagnosis. You need laboratory analysis to indicate the precise origin of your microbial complication, or else you might miss the target with your treatment,” Dr. Pérez-Santonja said.

The correct procedure, he explained, is to lift the flap, take a sample and send it to the laboratory, where specific tests for mycobacteria and fungi (acid-fast staining and Lowenstein-Jensen’s agar) should be performed in addition to the routine tests for microbial keratitis.

“Then, scrape the stroma, irrigate the interface and put the flap back, but use the right broad-spectrum antibiotics during irrigation,” he said.

The usual combination of fortified cephazolin and tobramycin, respectively covering the gram-positive and the gram-negative spectra, is not appropriate in case of post-LASIK microbial keratitis.

“Fortified cephazolin (50 mg/mL) is fine, but I strongly suggest fortified amikacin (10 mg/mL) in place of tobramycin, as it provides coverage not only for gram-negative bacteria, but also for mycobacteria, which have almost 30% chances of being the determining factor in your complication,” he said.

The same combination of topical antibiotics is then administered every hour for 2 days. If there are signs of clinical improvement, medications can be given at longer intervals of 2 hours for up to 5 days.

“At that point, you can change to regular-strength antibiotic drops, and slowly taper off, depending on the progression of clinical improvement. Once the organism has been identified, you can also consider additional treatment with topical steroids,” Dr. Pérez- Santonja said.

Prevention

Personally, Dr. Pérez-Santonja has seen about 10 cases of this complication.

“We were not successful with all of them, but since we have adopted this schedule of treatment, results have improved,” he said.

He also recommended some preventive measures to adopt during LASIK to lower chances of developing this complication.

“True sterile surgery is mandatory,” he said. “Use betadine, and use plastic drapes to isolate eyelashes and lid margins. Sterilize laser hand controls, and wear powderless sterile gloves. Use a different set of instruments and blade for each eye.”

Prophylactic antibiotics, he added, should be used for at least 5 days.

“Ofloxacin or ciprofloxcin are still the best antibiotics to use for prophylaxis, as more specific drugs for mycobacteria and fungi are too toxic to make it worth using them for prevention,” he said.

Mycobacteria and fungi are rare microorganisms in non-LASIK-related microbial keratitis.	About 40% of post-LASIK microbial keratitis are caused by gram-positive cocci as shown above.
Mycobacteria such as filamentous fungi originate post-LASIK microbial keratitis complications in 15% of cases.	Patients with microbial keratitis report moderate-to-severe pain, photophobia and impaired vision.

For Your Information:
Juan J. Pérez-Santonja, MD, can be reached at the Alicante Institute of Ophthalmology, Avd. De Denia 111, 03015 Alicante, Spain; +(34) 96-565-7465; fax: +(34) 96-526-0530; e-mail: jjpsantonja@coma.es.