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By Shirley Ha, BSc. (Hons), O.D.

Wearing contact lenses increases the risk of complications such as corneal infiltrative events (CIEs). Over the last few years, a growing number of reports show an increase in a newly classified, non-infectious CIE called contact lens-associated infiltrative keratitis (CLAIK). It is especially prevalent in patients using certain silicone hydrogel (SiHy) lens and multi-purpose solution (MPS) combinations[i]^,[ii],[iii].

Anecdotal cases from private practitioners are also on the rise, with two Minnesotaoptometrists recently claiming to have linked more than 35 cases of CLAIK to one leading contact lens solution.[iv]

Yet, according to Dr. Robin Chalmers and her team at the Indiana University School of Optometry, the incidence of CIEs was over three per cent per year in their retrospective chart reviews of 3,549 multiple-brand SCL wearers.[v]^,[vi] This is in agreement with Carnt et al., who also found a similar overall CIE incidence rate of 3.1 per cent with their 558 participants.[vii]

Additionally, 166 subjects, using more than 45 lens solution combinations in another retrospective, multicentre, case-control study showed no significant increase in CIE risk with any single contact lens brand, lens care product or combinations.[viii]

The relationship between “sterile” infiltrates and the use of SiHy-MPS combinations was first observed in 2007 when researchers identified fluorescein staining concomitant with infiltrates as a sign of cell cytotoxicity.[ix] Others suggested the corneal staining was not associated with infiltrates but rather related to the MPS preservatives binding to the fluorescein dye (PATH) and was transient and non-cytotoxic.[x]

Furthermore, new research is emerging to indicate that sodium fluorescein can enter and stain living or early apoptotic cells and solution-induced corneal staining (SICS) may not be an appropriate evaluation of solution toxicity anymore.[xi]

Some proposed that infiltrates come from the direct, physical insult associated with having a SiHy lens in the eye. The higher modulus SiHy material on the cornea, lids and adnexa triggers an antigenic or foreign body response to release inflammatory mediators that cause CLAIK, giant papillary conjunctivitis (GPC), corneal neovascularization, and mucin ball production.[xii] Also, SiHy fits are usually tighter than conventional hydrogels to prevent “fluting” or excessive edge lift. The poorer tear exchange, along with the absence of the blinking process on the back surface of the lens, allows debris, deposits and microbial biofilm, including released endotoxins, to build up and become additional stimuli for an immunological response.[xiii] The hypothetical pathophysiology may explain why some studies paradoxically show a two-fold greater risk for CIEs with silicone hydrogels than with conventional hydrogels.5

Other identifiable risk factors for CLAIK include, but are not limited to, exceeding the recommended wearing schedule and poor compliance, such as lack of hand washing, failing to rub and rinse contact lenses, case contamination, topping up solution, inadequate case hygiene, and not replacing cases at least once a month.[xiv]

Typically, patients with CLAIK will present with bilateral, small, diffuse, epithelial or sub-epithelial, grey, granular infiltrates in the central or entire cornea. They are different from the unilateral, single, round, sub-epithelial or anterior stromal, grey-white, mid-peripheral to peripheral infiltrates seen in infiltrative keratitis (IK) and in contact lens peripheral ulcers (CLPU) or the multiple, small-diffuse round white infiltrates seen 2-3 mm from the limbus in contact lens-associated red eye (CLARE).¹ The eyes can be white to moderately injected with no corneal oedema and there is no overlying NaFl staining. Patient symptoms can range from none to acute burning, redness and photophobia, with some reporting prior milder episodes of hyperaemia that disappear when they give their eyes a break from contact lens wear.¹

Fortunately, CLAIK can be treated without any long-term consequences. Because of its self-limiting nature, immediate lens cessation is a good place to start. Treatment can range from simple monitoring to prescribing topical ocular steroids, such as Lotemax or Pred Forte, or a combination antibiotic/steroid preparation, such as Tobradex, to decrease the microbial load. Once the signs and symptoms are resolved completely, wait at least eight days to see if the infiltrates reappear; if they do not, consider changing the lens care solution to another MPS or hydrogen peroxide system before loosening the fit or refitting to another SiHy or conventional hydrogel. Finish off with a discussion of lens hygiene and compliance or better yet, switch to a daily disposable lens without solution.¹ 

While it has been suggested that CLAIK may be associated with certain SiHy-MPS combinations, the non-consensus in clinical data make this debatable. Regardless of whether it is a growing problem or not, CLAIK is still a concern for the patient and the practitioner, especially if there are vision, ocular health and safety risks. Until we get definitive evidence that certain combinations of SiHy material and MPS cause CLAIK, it remains incumbent on the research community and lens product companies, in the interests of accurate diagnosis and appropriate risk management by eyecare professionals, to continue to investigate other aetiologies for CLAIK that might have been overlooked.