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Contact lens induced ulcerative keratitis is a serious complication which can be devastating for the patient if treatment is delayed. Extended wear is the commonest cause of microbial keratitis in contact lens wear.1 New extended wear silicone hydrogel contact lenses have higher oxygen transmissibility so that they can be worn continuously for 30 days. They can also be used as bandage contact lenses.
The risk of Pseudomonas microbial keratitis with overnight wear is significantly increased by contact lenses with low oxygen transmissibility.2 By virtue of high oxygen transmissibility, the silicone hydrogel contact lenses are thought to be associated with low risk of infectious keratitis.3,4 So far only four cases of microbial keratitis have been reported with their use.5 In spite of various claims of protection against serious microbial keratitis with pathogens such as P aeruginosa, we have recently come across the first case of Pseudomonas keratitis in a patient wearing silicone hydrogel contact lenses.
A 23 year old male patient presented with 1 day history of severe pain, ocular injection, photophobia, and reduced vision of right eye. He was wearing the day and night silicone hydrogel contact lenses, which was replaced once every 30 days (Ciba vision Focus day and night). He has been wearing these contact lenses for 7 months before the presentation.
Examination revealed a visual acuity of hand movement for the right eye and 6/5 for the left eye. The right eye had a central corneal ulceration of 3 mm in diameter surrounded by severe oedema and a 1 mm hypopyon. Cultures grew P aeruginosa and coagulase negative staphylococci both sensitive to ciprofloxacin and gentamicin. Topical ofloxacin and gentamicin were commenced with cyclopentolate. Unpreserved prednisolone eye drops (0.5%) were added after 1 week. Two weeks later, the epithelial defect had resolved leaving behind a central subepithelial corneal scar (fig 1). His vision improved to 6/18 unaided, 6/9 through the pinhole, 1 month after the admission.
The major barrier to prescribing a continuous wear contact lens is a perceived danger of microbial keratitis. Many factors are involved in the development of microbial keratitis and these include bacterial adherence to the lens surface, formation of bacterial glycocalyx on the lens, corneal hypoxia, deposits on the lens surface, and the effect of contact lens on closed eye environment.6 Silicone hydrogel contact lenses have high oxygen transmissibility and these lenses are colonised by similar numbers and type of micro-organisms compared with HEMA based materials.7 A number of studies have shown lower risk of infectious keratitis with new silicone hydrogel contact lenses.3,4
However, the use of silicone hydrogel contact lenses was associated with slightly higher levels of visible deposits,3 which may act as a risk factor for bacterial keratitis. As in our case young male patients were also considered a risk factor for contact lens induced microbial keratitis. Our experience suggests that extended wear silicone hydrogel contact lenses are not free of the risk of more serious microbial keratitis caused by P aeruginosa and coagulase negative staphylococci. With increasing popularity among optometrists and the use of silicone hydrogel contact lens as a bandage contact lens, such a serious complication cannot be ignored.
As suggested by other authors,6 our experience points towards a multifactorial aetiology for microbial keratitis, rather than just oxygen transmissibility. Further studies are required to find out the safety of the silicone hydrogel contact lenses with regard to development of microbial keratitis.