CME (February 2010)
Monthly Self-Study Series

Contact lens-related keratitis

Dr. NG Sin Yee, Anita
Honorary Clinical Assistant Professor, DOVS, CUHK
Specialist in Ophthalmology

Introduction

The corneal epithelium is a self-renewing, stratified epithelial sheet that provides the first-line defence against microorganisms invading the eye, and a smooth refractive surface important for vision. Ulcerative and non-ulcerative corneal infections (e.g. keratitis) are potentially blinding conditions that are generally only found in eyes with a predisposing element. Contact lens (CL) wear is a very important common risk factor in otherwise healthy eyes. The CL shares an intimate relationship with the epithelial surface, and all forms of CL wear, regardless of lens material and modality of wear, have a profound effect on the physiology of the cornea. Importantly, the physical existence of a CL, irrespective of oxygen transmissibility, disrupts corneal epithelial renewal mechanisms, producing a thinned, stagnant epithelium. This stagnation has been implicated as the cause of keratitis [1].

A previous study, conducted by the Chinese University of Hong Kong has indicated that the annual incidence of microbial keratitis in CL wearers is 3.4 per 10,000, with Pseudomonas aeruginosa as the dominant pathogen, followed by Acanthamoeba spp. [2]. However, in the past 2 to 3 years, it has been shown that there is an increase in the incidence of polymicrobial involvement [3], and also in outbreaks of Fusarium keratitis [4] and Acanthamoeba keratitis. These may have been due to contamination of CL solution, and the outbreaks gradually subsided after recall of the products.

Early diagnosis and treatment are important in the management of CL-related keratitis. Virulent infection could result in disruption of Descemet¡¦s membrane (a deeper layer of the cornea), and spread of the infection into the anterior chamber, causing endophthalmitis.

Clinical features

Patients complain of pain, redness, discharge, photophobia and blurred vision. The intensity of the symptoms depends on the type of infecting agent, the extent of the infection and especially the degree of corneal involvement.

Pseudomonas spp. typically causes thick mucopurulent exudate at the centre of the cornea (Figure 1) and also a semi-opaque, ground-glass appearance of the adjacent corneal stroma. The infection can progress rapidly and may result in corneal perforation within 48 hours.

Extreme pain is characteristic of Acanthamoeba spp. infection. The patient may complain of intense pain that may seem to be disproportionate to the extent of corneal involvement. The cornea may show patchy infiltrates and perineural infiltrates as a whitish line on the cornea. Later the infiltrates may enlarge and coalesce to form a ring abscess (Figure 2), and ulceration could follow, resulting in hypopyon formation.

Fungal keratitis is characterized by a greyish-white ulcer with indistinct margins. The lesions may be surrounded by delicate, feathery, finger-like infiltrates in the adjacent stroma (Figures 3 and 4).


Figure 1. A mucopurulent abscess at the visual axis.


Figure 2. Acanthamoeba keratitis with a ring abscess.


Figure 3. Fusarium keratitis with a greyish ulcer and indistinct margins.


Figure 4. Magnified view of Fusarium keratitis with a fluffy abscess and feathery edges.


Figure 5. Peripheral corneal infiltrates.


Figure 6. A corneal scar at the visual axis.

Differential diagnosis

Sterile corneal infiltrates may develop in patients with chronic CL wear. These infiltrates are usually small peripheral opacities (Figure 5). They are usually asymptomatic and are detected during routine ocular exams or by the patients themselves when they look at their eyes in the mirror. They usually disappear once CL wear has been discontinued. Resumption of CL wear is possible with a flatter fitting lens. Proper CL fitting procedure is strongly advised. It is essential to note that corneal infiltrates may be an early manifestation of microbial keratitis. If there is any doubt, referral to an ophthalmologist is advised.

Pathogenesis

The mechanism is multifactorial in nature. The reduced tear flow and stagnation in the post lens tear film of CL wearers increases the binding ability of microbes to the surface corneal epithelial cells by trapping or increasing bacterial exposure to the ocular surface. CL wear produces varying levels of direct corneal epithelial surface damage. This can disrupt the tight barrier function of the corneal epithelium, and exposes receptors on the underlying squamous cells. In addition to lens-induced corneal damage, the chemicals preserved in CL solution have been shown to induce a toxic effect on the cornea [5]. This could lead to a reduction of epithelial desquamation, and also up-regulation of bacteriabinding receptors on the corneal surface epithelial cells.

Treatment

Keratitis is a sight-threatening condition and urgent identification and eradication of the causative organism is warranted. Corneal scraping with a 25-gauge needle or spatula should be done under microscope, to ensure that the specimen is being taken at the margin of the lesion instead of the ulcer bed. The CL and also the case and the solution inside should be sent together with the scraping specimen for culture. Material should be plated on blood agar for the growth of aerobic organisms, thyoglycolate broth for facultative anaerobes, chocolate agar for Neisseria spp. and Haemophilus spp., sabouraud agar for fungi and non-nutrient agar preseeded with Escherichia coli culture for Acanthamoeba spp. detection.

Debridement of the necrotic tissue on the cornea should be performed at the same time as corneal scraping. This can enhance antibiotic penetration.

Before the result comes back, ¡§big-gun¡¨ antibiotic treatment should be initiated. Choices include fluroquinolone, fortified aminoglycoside and fortified cephalosporin. The regimen should be started according to the clinical features, and adjusted when the pathology results are available.

Outcomes are variable; if treatment is initiated early and the patient is responding effectively, vision may be preserved with no permanent damage to the visual function. However, most of the time, a corneal scar will be left (Figure 6), and, depending on the site, vision will be affected to a variable extent. Poorly controlled keratitis could result in corneal melting, and a therapeutic corneal transplant may be needed in some patients.

As most patients using CL are young and healthy, normal vision is important to them. Doctors should have a high awareness of keratitis when patients present themselves with red-eye and take a history of CL wear. The cornea should be examined carefully to rule out the presence of infiltrates. Early diagnosis and proper management is of paramount importance in preserving vision.

A note on orthokeratology (OKL)

Overnight wear OKLs have grown in popularity as an alternative to the irreversible refractive surgeries. Promotions and propaganda have boosted awareness, and in regions where the prevalence of myopia is high, such as southeast Asia, OKLs have gained in popularity.

There is a misconception that the use of OKLs can halt the progression of myopia. OKLs are designed so that their base curve is flatter than the central cornea, and therefore remodels the central cornea to alter the refraction of the eye. Patients need to wear OKLs at night, but they do not have to depend on spectacles during the daytime. Changes observed in the corneas of OKLs users include corneal oedema and abrasion. The lack of blinking during sleep means that there is a failure in disrupting the glycocalyx slime formed by bacteria, which in turn potentiates the risk of infection. OKLs can be associated with serious and vision-threatening complications.

References

  1. Chang JH, Ren H, Petroll WM, et al. The application of in vivo confocal microscopy and tear LDH measurement in assessing corneal response to contact lens and contact lens solutions. Curr Eye Res 1999;19:171¡V81.

  2. Lam DSC, Houang E, Fan DSP, et al. Incidence and risk factors for microbial keratitis in Hong Kong: comparison with Europe and North America. Eye 2002;16:608¡V18.

  3. Yu DK, Ng ASY, Lau WWY, et al. Recent pattern of contact lens keratitis in Hong Kong. Eye Contact Lens 2007;336:284¡V7.

  4. Ng ASY, Lau WWY, Yu DKH, et al. Clinical features and outcomes of Fusarium keratitis associated with contact lens wear. Eye Contact Lens 2008;34(2):113¡V6.

  5. Morgan PB, Efron N, Brennan NA, et al. Risk factors for the development of corneal infiltrative events associated with contact lens wear. Invest Ophthalmol Vis Sci 2005;46:3136¡V43.

Self-Assessment Questions
(Please indicate true or false to the following questions.)

1. CL wear is an uncommon predisposing factor to keratitis.

2. Sterile corneal infiltrates are usually located in the peripheral cornea.

3. Patients with Acanthamoeba keratitis typically present with excruciating eye pain.

4. Pseudomonas spp. typically causes central mucopurulent infiltrates.

5. A greyish-white feathery ulcer is typical of Acanthamoeba keratitis.

6. A perineural infiltrate is typical in Pseudomonas keratitis.

7. Orthokeratology can halt myopic progression.

8. Keratitis could result in corneal scarring, which may impair vision.

9. Properly fitted lenses will not result in keratitis.

10. Polymicrobial infection is becoming more common in CL keratitis.