To the Editor: Extended-wear silicone hydrogel contact lenses allow the convenience of 24-hour correction of refractive error and freedom from cleaning solutions and storage containers. However, they are associated with an increase in the risk of microbial keratitis when worn overnight compared with daily wear.1-5

The following cases from a single ophthalmology practice illustrate the risk to contact lens wearers when they use silicone hydrogel contact lenses overnight.

A 36-year-old woman presented 11 days after sleeping with her silicone hydrogel contact lenses in overnight. She had increasing right ocular pain and photophobia over the preceding 9 days, which had not resolved with chloramphenicol drops. On examination, visual acuity was 6/18 right and 6/6 left. Corneal cultures grew Acanthamoeba, which responded to polyhexamethylene biguanide and brolene drops hourly. Her final best corrected visual acuity was 6/9 right, 5 weeks later.

A 24-year-old woman presented with 2 days of left ocular pain, conjunctival injection, and epiphora following continuous silicone hydrogel contact lens use over the preceding week. On examination, visual acuity was 6/6 right and 6/18 left. A central corneal ulcer with stromal infiltrate and significant anterior chamber activity was present in her left eye (Box). Corneal cultures grew Pseudomonas aeruginosa, which responded to topical gentamicin 1% drops hourly. Her final best corrected visual acuity was 6/5 left, 3 weeks after diagnosis.

An 8-year-old girl was seen 2 months after commencing continuous wear of her silicone hydrogel contact lenses for uniocular myopia. She had worn the same lenses for 4 weeks continuously when she presented with a 2-day history of right ocular irritation, photophobia, and conjunctival injection. On examination, visual acuity was 6/36 right and 6/6 left. She was commenced empirically on cephalothin 5% and gentamicin 1% drops hourly. Corneal cultures did not grow any causative organism, and her clinical condition improved significantly over the following 7 days. Her final best corrected visual acuity was 6/9 right.

Although microbial keratitis may only affect a small proportion of individuals1,2,5 and our patients did not experience significant reduction in vision following treatment, microbial keratitis is potentially blinding and should not be trivialised.

Silicone hydrogel contact lenses have a lower risk of associated microbial keratitis than other lens types, but they do not remove it completely. In view of this, contact lenses should not be worn overnight or for an extended period. Furthermore, a painful red eye in a contact lens wearer should be considered microbial keratitis until proven otherwise, and needs a prompt ophthalmologist referral.

Microbial keratitis in a 24-year-old woman