Risk factors for CLMK
Our study is unique in that, not only does it investigate risk factors for microbial keratitis, but it also analyses the opinions of patients after corneal infection. This gives useful insight into how contact lens practitioners can improve patient education and compliance. This was only possible with face-to-face interviews as it allowed for a lot of detail to be gathered from participants, and also ensured full completion of the questionnaire. Completing the questionnaire did not lengthen waiting times, which meant that no patients dropped out of the study. Our most significant risk factors for CLMK identified included showering in contact lenses, being aged 25–54 and wearing certain soft contact lenses.
Monthly contact lenses were the most frequently used contact lens type in our patient cohort. All forms of contact lens wear increase the risk of microbial keratitis but monthly and extended wear contact lenses have previously been shown to increase risk of sight loss.1–3 Although monthly disposable lenses also increase the risk of infection, this did not reach statistical significance. In our patient group, 10.8% of patients reported significant sight loss, while 56.8% reported no change in their vision.
Pseudomonas aeruginosa is the most commonly identified pathogen among contact lens wearers followed by Gram-positive organisms.3 P. aeruginosa is able to adhere and colonise contact lens materials during lens wear, survive in contact lens storage cases and has resistance to contact lens disinfectants.14 Acanthamoebae are free-living cysts, forming ubiquitous protozoa found in air, dust, soil and fresh water. They are highly resistant to disinfection with chlorine and are thus not eradicated from tap water.15 16 For this reason, showering, swimming or washing contact lenses in fresh water can be considered risk behaviours. In our study, showering while wearing lenses was identified as a significant independent risk factor for CLMK. The univariate regression model showed the OR for showering in lenses was 3.1 (95% CI, 1.2 to 8.5; p=0.025), with a dose-dependent effect. The OR for showering in lenses daily, compared with never, was 7.1 (95% CI, 2.1 to 24.6; p=0.002). The OR for showering daily in lenses in the multiple regression model was 13.73 (95% CI, 2.35 to 80.07; p=0.004).
Equally, our study showed that sleeping in contact lenses increased the risk of microbial keratitis (OR, 3.1; 95% CI, 1.1 to 8.6; p=0.026) in the univariate model but this was not significant in the multivariate model. The effect of sleeping in lenses was replicated from previous studies,9 10 12 but these studies looked at overnight wear, whereas our study looked at sleeping in lenses for different amounts of time. The effects of contact lens-related hypoxia are likely increased in sleeping patients as oxygen diffusion is compromised when eyes are shut for a long time. Studies have shown that hypoxia can lead to increased binding of Pseudomonas to the cornea when a contact lens is present.17
Following an episode of CLMK, very few of our patients considered discontinuing contact lens wear. Of those whose quality of life or vision had been affected by the infection, 80% (n=20) wished to continue wearing their lenses, demonstrating the benefits that contact lens wear provide but also the importance of instilling good contact lens hygiene awareness and reinforcing this information when attending eye casualty. A large number of our participants (92.2%, n=72) identified the optician as being responsible for providing information about contact lens-related complications. Nearly half of all participants in both control and CLMK groups could not recall or were unsure if they were told specifically about the risks of contact lens-related infections when first prescribed their contact lenses (figure 1c).
Under guidance from College of Optometrists UK, contact lenses can only be fitted and prescribed by optometrists, doctors and contact lens opticians. Dispensers of contact lenses are required to give training and information about lens care, hygiene and wear schedules before lenses can be dispensed. About 89.2% (n=33) of the patients who developed microbial keratitis, stated that an optician supplies them with their contact lenses. The British Contact Lens Association (BCLA) recommends contact lens aftercare appointments at least annually. As shown in table 3, non-compliance with annual aftercare appointments was not found to be a risk factor for microbial keratitis. There was a high level of reported compliance in attending annual follow-up appointments, in both cases and control group. A 2010 Australian study18 looking at contact lens compliance found similar results.
These findings are rather confusing, as despite regular follow-up with opticians and perceived good concordance with BCLA recommendations, patients’ understanding and retention of contact lens hygiene and risk behaviour remains low. As patients are likely to want to continue wear lenses even after an infective episode, contact lens practitioners should focus efforts on improving patient retention of information about infections and aftercare practices, because persuading patients to stop wearing contact lenses may be ineffective.
Our study demonstrated that all three forms of information—verbal, demonstrations and written—were important for contact lens wearers to improve education about lens wear and complications. A possible way to increase awareness may be to supply printed material with each contact lens box to remind them about risks and aftercare practices.
A limitation of the study was that controls were also eye casualty attendees, presenting with other ocular problems, which could have introduced bias into the control group. These patients, however, presented with non-ocular surface problems and non-contact lens-related issues, which were typical for any person attending the department. To limit recall bias in the CLMK cases group, only patients who were newly diagnosed with CLMK and still had active infection were included in the study. The questionnaire used was developed and validated by the research team, and face-to-face interviews were chosen to accurately obtain data. To limit interviewer bias and limit influencing participant responses, only one researcher who was not involved in patient care, conducted the interviews in a standardised manner. A limitation was that the OR and CI ranges in the multivariate model were large. A larger sample size would be needed to calculate a more precise estimate of effect.
Risk factors that could be investigated further include: overall duration (eg, in years) of contact lens wear, smoking history, socioeconomic status, ethnicity and reason for contact lens wear (hyperopia, myopia, presbyopia or cosmetic). A multicentre study with a larger sample size could reduce sample bias, help evaluate risks and demographics further, and could show trends on regional and national levels. Precision and the number of significant results may also be improved. An interesting area for future work would be to further investigate the effect of showering in contact lenses, and to identify which organisms are isolated in patients with CLMK who shower in lenses.
The major personal hygiene risk factors for CLMK include showering, especially daily, in contact lenses and sleeping in lenses. Patients aged 25–54 are the most at-risk group. Despite most contact lens wearers buying their lenses from opticians and having regular follow-up appointments, contact lens wearers continue to perform poor hygiene practices and risk developing microbial keratitis. Focusing attention on improving education of infection and retention of information may help improve compliance with lens wear practices, which may help reduce incidence of CLMK and associated sight loss.
