July 2008

 

OPHTHALMOLOGY NEWS

 

Microbial keratitis & orthokeratology studied


by Matt Young EyeWorld Contributing Editor

 

 

The majority of cases found in East Asia

Charles Kaiser, M.D., wore his orthokeratology lenses overnight, and, in general, is happy with his vision; however, orthokeratology still poses safety challenges Source: William Trattler, M.D.

Although orthokeratology has emerged as a viable vision-correction procedure, it still poses safety challenges. A study published in the November 2007 issue of Eye & Contact Lens found that 123 cases of microbial keratitis have been reported in association with the procedure since 2001. Nearly 70% of cases were reported in East Asia, which should be a relief to those employing the procedure in the West. Still, affected patients have resided in the United States, Australia, Canada, Israel, and the U.K. China and Taiwan have been a hot spot for such cases, and Korea and Japan also made the list of affected countries. “The high prevalence of cases of Acanthamoeba keratitis reported with this modality emphasizes the importance of eliminating the use of tap water in care regimens for overnight orthokeratology,” wrote study co-author Helen A. Swarbrick, Ph.D., School of Optometry and Vision Science, University of New South Wales, Sydney, Australia.

Study highlights

The study researchers looked at cases of microbial keratitis associated with orthokeratology identified from literature case reports. The first 50 cases were reported in one study in 2005, and an additional 73 have been reported since then up to this study’s publication. China had the most cases from the 73 most recent reports, at 28 cases, followed by Taiwan (25 cases), Australia (seven cases), Canada (three cases), Korea (five cases), the United States (two cases), Israel (one case), Japan (one case), and the U.K. (one case). Most patients of the entire series were female (79 in all). Men comprised 41 cases. Three cases were bilateral. “There have been an increasing number of published reports of microbial keratitis associated with orthokeratology lens wear in the last seven years,” Dr. Swarbrick reported. Nonetheless, regardless of publication date, Dr. Swarbrick noted that the peak of microbial keratitis occurrence in orthokeratology was in 2001. The poorest outcomes also occurred in China. “The final BCVA [best-corrected visual acuity] was reported in 20 cases and was 20/200 or worse in nine of these cases,” Dr. Swarbrick reported. Overall, final BCVA (reported in 93 cases) was worse than 20/200 in 17 cases (18%), but results appear to have improved. “Since 2003, only two additional cases of microbial keratitis that resulted in BCVA worse than 20/200 have been reported; both involved Acanthamoeba infections,” Dr. Swarbrick said. Microbial keratitis did result after sustained lens wear—a period of days to more than a dozen years. “The range was from three days of continuous wear (one case) to 13 years (one case), and the median amount of time was 12 months,” Dr. Swarbrick noted. “Most (73 [92%]) patients wore their orthokeratology contact lenses overnight, with no contact lens wear during the day. Other lens-wearing modalities included orthokeratology contact lens wear on alternate nights (one case), daily wear (three cases), and extended wear (two cases).”

The main pathogens identified among the cases included Pseudomonas aeruginosa (46 cases, 37%), and Acanthamoeba (41 cases, 33%). “Acanthamoeba infections typically take longer for diagnosis and beginning of treatment and thus often result in poorer visual outcomes,” Dr. Swarbrick reported. Others included Serratia marcescens, Xanthomonas maltophilia, Nocardia asteroides, Providencia stuartii, Burkholderia cepacia, Pseudomonas putida, staphylococci, and Haemophilus influenzae. The reasoning behind the infections is partly regulatory. “The orthokeratology contact lens market in China was unregulated in 2001,” Dr. Swarbrick noted. The government eventually intervened to stop the health issue. Still, the infections did persist beyond China, including Canada and the United States (where Acanthamoeba infections did occur), and in concerning volume. “In a typical case series of microbial keratitis in other modalities of contact lens wear, a prevalence of 3% to 5% would be expected for Acanthamoeba infections,” Dr. Swarbrick noted. “Thus, the high prevalence of Acanthamoeba infections associated with overnight orthokeratology (33% in this series) is cause for concern.”

Moving forward, Dr. Swarbrick recommended eliminating tap water from orthokeratology care and maintenance, and ensure optimal fitting in children. Then again, Sam Fulcher, M.D., Temple, Texas, advised against performing orthokeratology at all. “The risk of complications is high,” he said. “I have zero interest in orthokeratology. I think there are better ways to manage [visual] problems, and I personally don’t know of any ophthalmologist that uses orthokeratology.” In fact, Dr. Fulcher said, his practice does not employ the use of extended wear contact lenses except in therapeutic cases. “The risk of infectious keratitis is so much higher with extended wear lenses,” he said.

Editors’ note: Dr. Fulcher has no financial interests related to his comments. Dr. Swarbrick has no financial interests related to this study.

Contact Information

Fulcher: 254-724-2111, sfulcher@swmail.sw.org

Swarbrick: h.swarbrick@unsw.edu.au

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