A. Seven reports overseas illustrate a possible link between overnight orthokeratology and bacterial corneal ulcers. The most recent was published in the March issue of Ophthalmology.
The study, done by Hong Kong researchers, included six case re-ports of children ages 9 to 14 who wore contact lenses overnight for orthokeratology and subsequently developed corneal ulcers and loss of best spectacle-corrected visual acuity due to scarring.1 (Five of the six patients tested positive for Pseudo-monas aeruginosa.)
Pseudomonas infection is somewhat rare in rigid lens wearers. But, the recent ARVO report by N. Yamamoto, P.M. Ladage and H.D. Cavanagh at Southwestern University in Dallas, showed a slight increase in Pseudomonas binding rates in rabbits with the use of orthokeratology designs when compared with controls using conventional lenses of the same material.2 Its unclear, however, as to how significant this may be and whether the results generalize to human subjects.
Despite the Hong Kong researchers efforts to identify the patients lens material (type and brand), diameter, power, base curves used, changes in corneal topography and fitting characteristics, such information was not made available.
Still, the researchers offer these theories about possible causes:
Children are more prone to trauma and are often not fully compliant in terms of maintenance and hygiene.
The compressive forces exerted by these lenses in the redistribution of corneal epithelium may result in local trauma at compressive points of the contact.
An already edematous ocular surface associated with nocturnal lens wear may render the corneal surface more susceptible to ulceration.
Serious infections may occur even with just overnight wear, as opposed to either extended wear (24 hours a day) or extensive daily use of contact lenses because of increased corneal hypoxia.
Several overseas reports have illustrated a possible link between orthokeratology and corneal ulcers.
There is no discussion in any of these case reports about how these lenses were fit or even if they were fit properly, adds Joel A. Silbert, O.D., director of the Cornea and Specialty Contact Lens Service at the Eye Institute. We also dont know what type of lens was used, and we have no information as to whether they were using high Dk materials.
So, should these studies influence our current practice here in the United States? No, says Dr. Silbert. We cannot let these studies panic us and allow the people who write them to imply that ortho-K as a procedure is unsafe because thats not true, he says. And I think statistically, if someone looks at these studies, its a miniscule percentage.
1. Young AL, Leung AT, Cheng LL, et al. Orthokeratology lens-related corneal ulcers in children: a case series. Ophthalmology 2004 Mar;111(3):590-5.
2. Yamamoto, N, Ladage, PM, Cavanagh, HD. Pseudomonas aeruginosa binding to the rabbit corneal surface following orthokeratology lens wear. ARVO abstract 1582, 2004.
3. Chen KH, Kuang TM, Hsu WM. Serratia marcescens corneal ulcer as a complication of orthokeratology. Am J Ophthalmol 2001 Aug;132(2):257-8.
4. Lu L, Zou L, Wang R. Orthokeratology induced infective corneal ulcer. Zhonghua Yan Ke Za Zhi 2002 Nov;37(6):443-6.
5. Hutchinson K, Apel A. Infectious keratitis in orthokeratology. Clin Experiment Ophthalmol 2002 Feb;30(1):49-51.
6. Young AL, Leung AT, Cheung EY, et al. Orthokeratology lens-related Pseudomonas aeruginosa infectious keratitis. Cornea 2003 Apr;22(3):265-6.
7. Lau LI, Wu CC, Lee SM, Hsu WM. Pseudomonas corneal ulcer related to overnight orthokeratology. Cornea 2003 Apr;22(3):262-4.
8. Wang JC, Lim L. Unusual morphology in orthokeratology contact lens-related cornea ulcer. Eye Contact Lens 2003 Jul;29(3):190-2.