Introduction

Silicone hydrogel lenses have been on the market since 1999 and the first cases of microbial keratitis associated with these lenses was published in 2002 [1] describing three cases treated in Melbourne, Australia. A number of other case reports have now been published [2-5], including cases where lesions were culture proven and permanent visual impairment was the result [2]. Since these reports, prospective studies have commenced around the world investigating the incidence of microbial keratitis with new lens types. In the UK, surveillance and case control studies have been published from Manchester Royal Eye Hospital [6, 7] and a case-control study is coming to a close at Moorfields Eye Hospital [8]. In Australia and New Zealand, the national surveillance studies concluded in late 2004 [9].

The case described here is amongst those reported in the national surveillance study in Australia. This case is fairly typical in its disease duration, demonstrates some of the risk factors identified in this prospective study and was successfully managed with topical antibiotic therapy.


Case Study

K.S., a 41-year-old female had been wearing silicone hydrogel contact lenses successfully on an extended wear basis for 3½ years and was traveling around Australia in late 2003. She inserted a new pair of silicone hydrogel contact lenses (lotrafilcon A) on December 26^th, 2003. After five days of continuous wear, on December 31^st, 2003 she removed the lenses due to eye pain and stored them in a multipurpose lens care solution for five days.  The lenses were reinserted on January 4^th, 2004 and were removed again nine days later with the same eye pain on 13^th January.  At this time, K.S. found her eye pain worsened, despite contact lens removal. She presented to her optometrist in her home-town and was referred on to an ophthalmologist for treatment on January 15^th, 2004. 

The Nullabor region spans approximately 300 km of remote road across a vast treeless plain. There are very few towns along the road, and water supply is limited at best. Town water is rationed because it is transported by truck.

There are several points of note from this history. The circumstances were complicated by the fact that she was traveling in remote Australia (Nullabor, see inset) at the time of her symptoms. During her travels she had showered while wearing the lenses and the water quality may have been less than optimum and a source of contamination. Moreover, the patient would have been remote from healthcare in this sparsely populated region of Australia and this may have increased the likelihood of delays in receiving treatment. She first saw her ophthalmologist on January 15, approximately 48 hours after the onset of symptoms.

Upon presentation, aided visual acuity was 6/6^-2 in the left eye.  Slit lamp examination of the left eye revealed a generalized conjunctival response with mild anterior chamber reaction.  There was a 1.2 x 1.0 mm infiltrate with an overlying epithelial break in the superior, paracentral region of the cornea above the line of sight.

K.S. was diagnosed with microbial keratitis related to contact lens wear, and was admitted to the hospital, immediately starting treatment with ciprofloxacin (0.3%), gentamicin (0.3%) and chloramphenicol (0.5%) eye drops hourly over 4 days. After 16 hours, a higher concentration of gentamicin (0.9%) became available and was used.

A corneal scrape was performed but the contact lenses had been discarded by the patient and were not available for processing. No growth was recovered from the corneal scrape.

After spending three nights in hospital, she was discharged and her medications were tapered over the coming weeks. She was referred back to her optometrist regarding her contact lens wear. Final visual acuity was 6/5 and a small, paracentral corneal scar remained.


Conclusion

This case demonstrated a case of microbial keratitis, which while not culture proven, was clinically consistent with this diagnosis. In other studies of microbial keratitis, the rate of positive culture varies between 36 and 64% [10-12] in presumed contact lens-related microbial keratitis, so a negative culture result is not unexpected and depends on many factors such as laboratory processing and sampling technique.

This case highlighted a number of behaviour patterns, which have been confirmed as risk factors for corneal infection in contact lens wear. First, overnight wear has been found to increase the risk of a corneal infection by 4 to 7 times and this patient habitually wore her lenses on an extended wear schedule. We have also found that travelers are more at risk of acquiring microbial keratitis [13]. It is possible that being away from home means reduced compliance with usual hygiene practices and certainly traveling in remote Australia meant exposure to potentially unhygienic conditions.

Other factors contributing to this complication may have been the long duration of contact lens storage (9 days) before resuming wear. It is possible that the original discomfort was associated with contact lens contamination and re-using these lenses after storage may have meant re-inoculation and the opportunity for micro-organisms to colonise the corneal surface.

Remoteness from healthcare increases the severity of contact lens related microbial keratitis as does delays in appropriate treatment [14]. In this case the delays in receiving treatment may have lead to more established disease requiring hospital treatment. In our research just 29% of cases of contact lens related microbial keratitis are treated as in-patients.

This case study is an excellent demonstration of an occurrence of microbial keratitis in an otherwise healthy and successful contact lens wearer. A number of factors were identified which can moderate the risk of corneal infection; overnight wear, inappropriate contact lens storage and contact lens use while traveling. To ensure that contact lens wearers make well-informed decisions about how they choose to wear and care for their contact lenses, practitioners must repeatedly educate and advise their patients of high risk behaviour.


Acknowledgments:

The authors would like to thank Nancy Keir for her contribution to the preparation of this case report.


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