Microbial keratitis associated with extended wear of silicone hydrogel contact lenses

Traditional hydrogel soft contact lenses (SCL) have limited oxygen permeability.^{1, 2} Recently introduced silicone hydrogel SCL have much higher oxygen transmissibility (Dk/t O₂), allowing near normal oxygen supply to the cornea during extended lid closure, and are hoped by some to address most of the problems related to corneal hypoxia encountered with previous extended wear soft contact lenses.^{1, 3} They have therefore been approved for up to 30 days of continuous wear in both Europe and Australia.

Four cases of microbial keratitis in patients who were using silicone hydrogel SCL (either CibaVision Focus Night and Day lenses (Lotrafilicon A, fluorosiloxane hydrogel) or Bausch & Lomb PureVision lenses (Balafilcon A, silicone hydrogel)) on an extended wear basis are presented. The minimum amount of continuous wear was 24 hours. All cases were treated either in private or at the corneal clinic of the Royal Victorian Eye and Ear Hospital from December 2000 to February 2001. All the patients underwent a complete ophthalmic examination by a corneal specialist. Microbiological specimens were taken from all patients via cornea scrapings and were submitted for Gram and Blankophor staining, and bacterial and fungal cultures via direct inoculation onto sheep blood agar, chocolate agar, and Sabouraud agar. Bacterial sensitivities of cultured organisms were also obtained. Where possible, the contact lenses themselves were also sent for microbial cultures.

Each case is described in brief, and a summary presented in Table 1.

Table 1.

Summary of case details

	Patient details
	Case 1	Case 2	Case 3	Case 4
Sex	Male	Male	Male	Male
Age	22	16	21	17
Eye	Left	Left	Right	Left
Refraction	−1.75/−0.25×50	−4.50	−3.50	−5.00/−1.50×5
Lens brand	CibaVision Focus Night and Day	Bausch & Lomb Pure Vision	Bausch & Lomb PureVision	CibaVision Focus Night and Day
Duration of EWSCL use	12 months	12 months	6 weeks	12 months
Pattern of wear	Monthly continuous wear	Monthly continuous wear	Daily wear, changing to 24 hours' continuous wear just before presentation	Monthly continuous wear
Duration of wear	10 days	7 days	24 hours	2 days
Microscopy	Insufficient specimen, no PMN or organisms seen	Fungal elements on Blankophor preparation. No organisms on Gram stain	PMN +, no organisms seen	No PMN, no organisms seen
Culture	Serratia marcescens (sheep blood agar plate)	Acinetobacter (enrichment broth) Penicillium (Sabouraud agar)	Heavy growth of Corynebacterium (sheep blood agar plate)	α Haemolytic streptococcus, in enrichment broth
Contact lens culture	Serratia marcescens	Yeast from left lens; Penicillium from right lens	Not available	No growth
Other risk factors	Swam in lenses 2 weeks earlier	Swam in lenses 1 week earlier		Swam in a different pair of lenses 3 days earlier
Last corrected VA (time)	VAR=6/6–1 (2 weeks)	VAL=6/7.5 (8 days)	Unavailable	VAL=6/7.5 (1 week)

Case 1

This 22 year old man presented with a 2 day history of left ocular injection, pain, photophobia, and blurred vision. He was wearing CibaVision Focus Night and Day SCL continuously for 10 days at a time, discarding the lenses after a month of use. He had swum in the sea while wearing the same lenses 2 weeks before, after which he removed the lenses and disinfected them in “Complete Comfort Plus” multipurpose solution (polyhexamethyl biguanide, poloxamer, hypromellose, edetate disodium, sodium phosphate dibasic and monobasic, sodium chloride, potassium chloride, purified water, manufactured and distributed by Allergan Australia, Sydney). Continuous wear was recommenced the next morning.

Examination revealed a visual acuity with his spectacle correction of 6/4-2 right eye and 6/9 left eye. The left eye had a central, 1 mm corneal epithelial defect with an underlying dense infiltrate. Marked ciliary injection and anterior chamber activity were present with 3+ cells and multiple inferior keratic precipitates (KP).

Serratia marcescens grew on the sheep blood agar plate from the corneal scrapings and the contact lens. It was sensitive to ciprofloxacin, tobramycin, and chloramphenicol.

Hourly topical ciprofloxacin 0.3% (Ciloxan, Alcon, Fort Worth, TX, USA) was commenced, with marked symptomatic improvement and resolution of the anterior chamber inflammation after 48 hours. Treatment was tapered and unpreserved prednisolone phosphate 0.5% drops were added four times daily. Review 2 weeks later revealed a best corrected visual acuity of 6/6-1 in both eyes, and a central subepithelial scar

Case 2

A 16 year old boy presented with a 24 hour history of left eye grittiness, marked photophobia, and hazy vision. He was wearing PureVision SCL on a monthly continuous wear basis. He gave a history of swimming in a river in these lenses 1 week earlier, after which he removed the lenses and disinfected them with “Renu” multipurpose solution (boric acid, edetate disodium, poloxamine, sodium borate, sodium chloride, and polyaminopropyl biguanide, manufactured and distributed by Bausch & Lomb, Greenville, SC, USA). Continuous wear was recommenced within a few hours.

Examination revealed an uncorrected visual acuity of 3/60 in both eyes, improving to 6/12 in both eyes with pinhole. A paracentral 1 mm epithelial defect with underlying dense infiltrate was noted in the left eye with anterior chamber inflammation of 1+ cells and multiple scattered KP (Fig 1).

Figure 1.

Case 2, left eye 1 day after presentation.

Corneal scrapings revealed fungal elements on Gram and Blankophor staining. Cultures grew Acinetobacter species in the enrichment broth, sensitive to ciprofloxacin, chloramphenicol, and tobramycin. Penicillium was later grown on the Sabouraud agar slope. A yeast (not Candida albicans) was grown on Sabouraud agar from the left contact lens, with Penicillium species grown from the right.

Topical ciprofloxacin 0.3% was commenced hourly, after which his symptoms and signs markedly improved. The ciprofloxacin was tapered and changed to topical chloramphenicol 0.5% (Chlorsig, Sigma) 8 days after presentation.

Two weeks later, the epithelial defect had resolved but significant subepithelial scarring remained. His best corrected visual acuity was 6/6 right eye and 6/7.5 left eye.

Case 3

A 21 year old man was referred to MSL with a 2 day history of right eye injection, pain, photophobia, and decreased vision. He was wearing PureVision lenses on a daily wear basis, but changed to continuous wear 24 hours before the onset of his symptoms.

Examination revealed a visual acuity of 6/6 right eye and 6/5 left eye with his spectacle correction. Marked right eye ciliary injection and anterior chamber activity were noted with cells, flare, multiple scattered KPs, and a small paracentral epithelial defect with underlying infiltrate.

Corneal scrapings revealed polymorphs on Gram stain (no organisms seen), and a heavy growth of Corynebacterium species on the sheep blood agar plate, sensitive to penicillin, ciprofloxacin, and chloramphenicol. Culture of the contact lenses was impossible as they had been discarded.

Treatment consisted of hourly topical ciprofloxacin 0.3%. Topical fluoromethalone acetate 0.1% (Flarex, Alcon, Fort Worth, TX, USA) was added four times daily after clinical improvement 24 hours later. All treatment was tapered and ceased after 2 weeks.

The patient failed to attend for any further follow up appointments but on contact by telephone stated his vision had returned to normal.

Case 4

A 17 year old presented with a 5 day history of left eye redness, irritation, photophobia, and blurred vision. He was wearing CibaVision Focus Night and Day SCL on a monthly continuous wear basis and gave a history of swimming in a river with a previous pair of lenses 3 days before the onset of symptoms. These lenses were discarded and replaced with his current lenses the next day.

Initial treatment by the general practitioner consisted of topical chloramphenicol (0.5%) drops 2 hourly by day and chloramphenicol (1%) ointment (Chlorsig, Sigma) at night.

Examination revealed a visual acuity of 6/6 right eye (with SCL) and 3/36 left eye unaided, improving to 6/18 with pinhole. Conjunctival injection was noted in the left eye, with a 3 × 4 mm paracentral area of stromal haze and an associated area of subepithelial infiltrate. The overlying epithelium was intact.

Corneal scrapings revealed no polymorphs or organisms on Gram stain, but grew α haemolytic streptococcus from the enrichment broth sensitive to penicillin, chloramphenicol, ciprofloxacin, and neomycin.

Treatment was with hourly topical ciprofloxacin 0.3%, with tapering after 48 hours. Review 1 week later revealed a persisting subepithelial scar and a best corrected spectacle acuity of 6/7.5.

Comment

Extended wear of soft contact lenses for up to 6 days has been advocated in various forms since the 1980s with traditional hydrogel lenses. However, owing to the relatively high rates of associated microbial keratitis,^{4, 5} extended wear of soft contact lenses has not had widespread use.

The advent of high oxygen permeability silicone hydrogel soft contact lenses has again made extended wear a viable option, as the increased oxygen permeability is thought to reduce the risk of development of a hypoxic epithelial defect, which can serve as a portal of infection.³ Pre-release extended wear studies did not reveal any cases of microbial keratitis but these studies were relatively small. Lenses with a Dk/t O₂ greater than 50 × 10⁹ have also been shown to have a lesser affinity for P aeruginosa binding during extended wear,⁶ further decreasing the risk of microbial keratitis.⁷

Our experience suggests that extended wear with even these newer SCL is still a risk factor in the development of microbial keratitis. All four patients had central or paracentral infiltrates, with three patients presenting with an associated epithelial defect. All four patients also had a positive culture or Gram/Blankophor stain from the corneal scrape and had residual scarring after resolution of the acute episode. Although Corynebacterium species are considered by some to be a non-pathogenic organism, it has been described as the causative organism in several cases of microbial keratitis.^{8, 9} We therefore feel that it is very unlikely that any of these cases represent a more benign non-infectious contact lens complication such as CLPU (contact lens induced peripheral ulcer), CLARE (contact lens induced acute red eye), or IK (infiltrative keratitis), which are all described as being conditions that resolve after cessation of contact lens wear alone, without the development of residual corneal scarring.¹⁰

Previous studies have shown that the most important risk factor for the development of microbial keratitis in soft contact lens wearers is the duration of contact lens wear, where overnight wear in particular aggravates the relative hypoxia of the cornea.^{5, 6} However, there are other risk factors such as hypercapnia, trauma, biofilm alterations/contamination, altered corneal sensation, altered tear volume, and composition.^11–13 Only hypoxia and hypercapnia should be improved by increased contact lens gas permeability.

Three of the four patients described had swum in their lenses within weeks of their presentation. This might be an important risk factor in the development of their microbial keratitis in association with their silicon hydrogel SCL (as it is with other SCL), although the organisms involved were not those typically associated with microbial keratitis from contaminated water exposure. All four of the patients were also males between the ages of 16 and 22 years. These two demographic factors have been linked to an increased risk of microbial keratitis in contact lens wearers.⁷

Recent studies have shown that bacterial populations grown from silicone hydrogel SCL in asymptomatic wear were not statistically different in comparison with those grown from standard HEMA based SCL.³ This suggests that a silicone hydrogel SCL can still be a means of contamination in the pathogenesis of SCL microbial keratitis. Certainly, some of the lenses in this small series did grow the same organisms as the corneal lesions themselves.

Our experience supports a multifactorial causality for the development of microbial keratitis in extended SCL wearers, rather than just corneal epithelial hypoxia, particularly in high risk groups such as the four patients described where high risk behaviour is also undertaken. Further investigation needs to be done on the effects these lenses have in extended wear with regard to the development of microbial keratitis before their long term safety can be assured.