Skip to main content
NCBI home page
Wiley Open Access Collection logoLink to Wiley Open Access Collection
. 2024 Nov 14;103(3):289–294. doi: 10.1111/aos.16796

Incidence, risk factors, and patient characteristics in severe contact lens‐related microbial keratitis

Martin Harvey Sund 1,2,✉, Jon Klokk Slettedal 3, Marit Sæthre 4, Hans Petter Haslev 4, Olav Kristianslund 2,4, Atle Einar Østern 4, Liv Drolsum 2,4
PMCID: PMC11986396  PMID: 39540620

Abstract

Purpose

The aim of the present study was to determine the incidence, patient characteristics, and risk factors for severe, contact lens‐related keratitis in patients in need of hospitalization.

Methods

Keratitis was defined as severe when the disease required hospitalization. All patients with contact lens‐related keratitis hospitalized at our department between 1 January 2018 and 31 December 2020 were interviewed with a questionnaire, about their use of contact lenses and knowledge of complications. Clinical information was collected from the medical records.

Results

A total of 41 patients (42 eyes) were hospitalized with severe keratitis during the 3‐year period. The yearly incidence was 2.52 per 10 000 contact lens users over the age of 15 for extended‐wear lenses used overnight, and 0.52 per 10 000 for users of daily disposable contact lenses. Pseudomonas aeruginosa was the most frequently isolated microbe. The median age was 50 years (range 15–66 years). Twenty‐three patients (56%) were female, 28 patients (66%) used extended‐wear contact lenses and 12 patients (29%) used daily disposable lenses. Nineteen patients (45%) admitted improper use. The median duration of contact lens use was 11.5 years. Only 15 patients (37%) had knowledge of keratitis as a potential complication.

Conclusion

Most patients were experienced contact lens users. Users of extended‐wear contact lenses worn overnight had a significantly higher risk of severe microbial keratitis. More focus on information and education of the risk of keratitis in contact lens users is needed.

Keywords: contact lens, incidence, microbial keratitis, pseudomonas

1. INTRODUCTION

The use of contact lenses is a major risk factor for developing microbial keratitis, which, in severe cases, can cause permanent loss of vision. A review article using statistics collected from a number of countries in different climatic regions found that 34%–50% of cases of bacterial keratitis were caused by contact lens wear, and that 25%–29% of cases with fungal keratitis, and 85%–93% of cases with Acanthamoeba keratitis were attributable to contact lens wear (Zimmerman et al., 2016). The increased risk of keratitis seen with contact lens usage is likely multifactorial. Factors such as biofilm formation on contact lenses, lens inhibition of epithelial sloughing, and contact lens wear causing reduction of antimicrobial activity of the tear fluid have been implicated in the pathogenesis (Fleiszig et al., 2020). The most common causative organisms vary by climate. In general, Pseudomonas aeruginosa is most frequently isolated, followed by gram‐positive bacteria, fungi, and Acanthamoeba (Stapleton & Carnt 2012). The incidence of contact lens‐related keratitis ranges from ~ 2–20 cases per 10 000 wearers (Fleiszig et al., 2020).

Soft contact lenses were introduced in the 1960s and 1970s. Initially, soft contact lenses had a low oxygen permeability, but this improved after breakthroughs in material technology in the following decades. In the late 1990s, silicone hydrogel contact lenses with a very high oxygen permeability were made commercially available. It was thought that this would lead to a decrease in the incidence of contact lens‐related keratitis, but the rates have remained unchanged (Stapleton et al., 2013).

Several studies have evaluated strategies for reducing the incidence and morbidity of contact lens‐related keratitis. Important factors include avoiding delay of treatment, avoiding overnight use, and ensuring proper lens hygiene. The use of daily disposable contact lenses is associated with less severe disease (Stapleton & Carnt 2012). Few studies exist addressing severe contact lens‐related keratitis specifically, in a Northern European temperate climate zone.

The primary aim of this study was to determine the incidence of contact lens‐related keratitis requiring hospitalization in the Norwegian temperate climate. The secondary aims were to determine the characteristics of the patient population, and to gain knowledge of which patients are more likely to develop keratitis.

2. MATERIALS AND METHODS

We included all patients with severe contact lens‐related keratitis from 1 January 2018 to 31 December 2020 treated at the Department of Ophthalmology, Oslo University Hospital. Severe keratitis was defined as patients requiring hospitalization. The need for hospitalization was evaluated in each case, but typically, these patients had large (>1 mm) microbial ulcers, and/or microbial ulcers in the visual axis, requiring daily examination and fortified eye drops prepared at the hospital. In practice, all patients with severe keratitis are admitted to the hospital. Only contact lens users were included in the study.

A structured interview was prepared specifically for this study. The interview contained questions about contact lens use (type, duration of use, place of purchase, improper use), and knowledge of potential complications from the use of contact lenses. Types of contact lenses were categorized as daily disposable, extended‐wear lenses approved for overnight use and extended‐wear lenses intended only for daytime use. The interview was performed on the second or third day after hospitalization by one of three doctors (MHS, JKS or MS). All eyes were photographed, and the location and size of the corneal ulcer(s) were registered. The following information was collected from the patients' medical records: Age, gender, vision at the time of hospitalization, refraction, laterality of the eye, other diseases, and whether patients had been treated with antibiotics and/or other eye medication prior to admission. Improper use was defined as using contact lenses for longer than recommended by the manufacturer, or as sleeping while wearing contact lenses not intended for overnight use. For two patients, we were unable to obtain information about the duration of contact lens use.

Incidence was calculated using the number of people 15 years and older in the hospital's primary area (919 844 in 2019) as the denominator (Statistics Norway, 2023). The data on the percentage of contact lens users in Norway is based on a telephone survey where 1421 people 15 years and older were interviewed. The authors concluded that 16% use contact lenses (Eva Livgard, Kantar 2022, pp. 25, unpublished). A different publication reports that 44% of contact lens users in Norway used daily disposable contact lenses, 27% used extended‐wear lenses intended only for daytime use and 18% used extended‐wear lenses approved for overnight use (Morgan et al., 2020). Estimates of the number of users of daily wear rigid gas‐permeable contact lenses in Norway are uncertain, and we have therefore abstained from calculating the incidence in this population.

Microbial sampling was performed using a swab stored in Stuart's medium to detect bacteria and fungi, while another swab stored in UTM‐medium was sent for PCR analysis to detect viruses. In addition, with the patients placed in a slit lamp, a corneal scrape was performed using a Kimura spatula. The material was seeded onto a chocolate agar plate, and afterwards dipped in serum broth. Samples for detection of Neisseria gonorrhoea, Chlamydia trachomatis, or Acanthamoeba were only taken in cases of clinical suspicion. In the latter case, antibiotic treatment was halted for 3 days, and corneal biopsies were deposited on non‐nutrient agar plates with a lawn of E. coli and observed daily for up to 2 weeks. All samples were sent to a specialized microbiological department at our university hospital and processed in accordance with professional standards. As a rule, samples were cultured for 2 weeks. In cases where fungal keratitis could not be ruled out, samples were cultured for three or more weeks.

Initially, all hospitalized patients received standard treatment for clinical bacterial keratitis in our hospital, using fortified eye drops containing gentamicin 13.3 mg/mL and cefuroxime 125 mg/mL. The eye drops were instilled every hour in the eye for the first few days and adjusted in accordance with microbiological findings.

Visual acuity was measured using Snellen acuity and later converted to logMAR. Counting finger‐vision was estimated to 20/2000 vision (logMAR 2), hand motion to 20/6000 (logMAR 2.5) and light perception to 20/20000 (logMAR 3).

The study was approved by the Regional Committee of Health Research Ethics. Written informed consent was obtained from every patient, or from their parents if the patient was under 18 years of age. The study followed the Tenets of the Declaration of Helsinki.

The data were tested for normality using the Shapiro–Wilk test. The test showed that the patients' ages were not normally distributed (p < 0.02). Consequently, median age is used throughout the article. Odds ratio was calculated for incidences of keratitis in users of different types of contact lenses. A binomial test was performed to consider whether unilateral infections in the left eye were significantly more common than unilateral infections in the right eye. No parametric tests are used.

3. RESULTS

3.1. Incidence

A total of 42 cases of severe, contact lens‐related keratitis in 41 patients residing in the hospital's primary area were registered during the study. As shown in Tables 1 and 2, users of extended‐wear contact lenses approved for overnight use had the highest risk of keratitis. Users of daily disposable contact lenses had the lowest risk. There was no significant difference in the rates of keratitis between the users of daily disposable contact lenses and the users of extended‐wear contact lenses intended only for daytime use.

TABLE 1.

Incidence of severe, contact lens‐related microbial keratitis by type of contact lens.

Type of contact lens Incidence per 10 000 wearers
Extended wear, day and night 2.52
All types of contact lenses 0.95
Extended wear, daytime only 0.76
Daily disposable contact lenses 0.62
Open in a new tab

TABLE 2.

Odds ratios of severe contact lens‐related microbial keratitis comparing wearers of different types of contact lenses.

Type of contact lens Odds ratio
EW day and night vs. daily disposable lenses 4.07. 95% CI: 1.99–8.33, p = 0.0001 a
EW day and night vs. EW daytime only 3.33. 95% CI: 1.52–7.32, p = 0.0027 a
EW lenses of any type vs. daily disposable lenses 2.36. 95% CI 1.21–4.63, p = 0.0122 a
EW daytime only vs. daily disposable lenses 1.22. 95% CI: 0.51–2.90, p = 0.6491
Open in a new tab

Abbreviation: EW, Extended wear.

a

Statistically significant.

Presentation was most common in the spring and autumn, and the month with the highest amount of hospitalizations was May with 11 (27%) patients. Nearly, half (19 patients; 46%) of the patients presented in the months of May, June and July.

3.2. Patient characteristics

As shown in Table 3, median age of the patients was 50, and ages ranged from 15 to 66 years. Twenty‐three patients (56%) were referred from urgent care clinics, 11 (27%) from primary care doctors, and two patients (5%) from ophthalmologists in private practice. The majority (28 patients; 68%) wore various types of extended‐wear‐contact lenses, and 12 (29%) wore daily disposable contact lenses. The patients had used contact lenses for a median time of 11.5 years.

TABLE 3.

Overview of patients hospitalized with severe, contact lens‐related microbial keratitis.

All patients (n = 41 a ) Users of daily disposable lenses (n = 12) Users of EW lenses intended for daytime use (n = 9) Users of EW lenses intended for overnight use (n = 19)
Female gender 23 (56%) 7 (58%) 6 (67%) 10 (53%)
Median age (range) 50 (15–66) 49 (21–57) 49 (15–60) 52 (21–65)
Median duration of use in years (range) 11.5 (1–47) 20 (4–35) 8.5 (1–31) 9.5 (1–47)
Improper use 19 (45%) 6 (50%) 5 (56%) 8 (42%)
Knowledge of keratitis 15 (37%) 7 (58%) 2 (22%) 6 (30%)
Positive cultures 31 a (74%) 8 (67%) 8 (89%) 14 (70%)
Open in a new tab
a

One patient used rigid contact lenses, and is not included in the subgroups.

Improper use was reported by 19 (45%) of patients. Twenty‐one patients used contact lenses intended only for daytime use, and nine of these patients (43%) regularly wore their contact lenses overnight. The majority of patients (27; 68%) purchased their contact lenses from opticians, and 11 (28%) of the patients purchased their contact lenses online.

3.3. Corneal scrapings and microbial analysis

Samples taken for microbiological analysis were positive in 31 eyes (74%). The most common causative organism was Pseudomonas aeruginosa (17 samples; 41%) (Table 4). In 11 cases, there was no microbial growth, and of those, six (55%) had been treated with antibiotics prior to presentation. Of the 31 cases with positive cultures, 17 (55%) had been treated with antibiotics prior to presentation. There was no significant difference in rates of positive cultures between users of any of the types of contact lenses.

TABLE 4.

Results of microbial cultures.

Result of microbiological tests Frequency Average size of corneal ulcers
Pseudomonas aeruginosa 17 (41%) 3.35 mm
Corynebacterium spp. 7 (17%) 1.44 mm
Acanthamoeba spp. 2 (5%) 6.30 mm
Cutibacterium acnes 2 (5%) 2.75 mm
Klebsiella oxytoca 1 (2%) 1.50 mm
Serratia marcescens 1 (2%) 1.00 mm
Staphylococcus epidermidis 1 (2%) 1.60 mm
Positive culture 31 (74%) 2.88 mm
Negative culture 11 (26%) 2.63 mm
Open in a new tab

Note: Frequency is the number of eyes with cultures positive for the microbe in the left column. The size of the microbial ulcers was measured in a slit lamp, and the average size was calculated for patients with the same causative microbe.

Simultaneous infection of both eyes was only observed in one patient. In patients with unilateral infection, the left eye (28 patients; 70%) was significantly more often affected than the right eye (12 patients; 30%) (p < 0.01). The size of the corneal ulcers varied between subgroups. Patients with cultures positive for Acanthamoeba spp. had the largest ulcers, with an average size of 6.30 mm.

3.4. Clinical findings

The median visual acuity at presentation was 0.82 logMAR (decimal equivalent 0.15), with considerable variation among patients (Table 5).

TABLE 5.

Best corrected visual acuity at presentation.

logMAR Decimal equivalent Number of eyes
>0.1 >0.80 3 (7%)
0.1–0.5 0.8–0.32 13 (32%)
0.5–1.0 0.32–0.1 9 (22%)
>1.0 <0.1 17 (41%)
Open in a new tab

3.5. Surgical interventions

Four patients (10%) suffered complications requiring surgical intervention. One patient underwent a corneal transplantation, the other patients underwent photorefractive keratectomy, phototherapeutic keratectomy, and amniotic membrane transplant.

4. DISCUSSION

Like other studies on this subject, we have found that the use of extended‐wear lenses intended for overnight use was associated with a substantially higher risk of microbial keratitis compared with the use of daily disposable contact lenses. Additionally, we found that a high proportion of patients were not aware of the potentially severe complications from their use of contact lenses. Interestingly, the patients in our study had a relatively high average age, and most were experienced users of contact lenses.

The odds ratio of severe microbial keratitis was 4.07 times higher for users of extended‐wear lenses approved for overnight use compared with daily disposable contact lenses, and 3.33 times higher compared with users of extended‐wear lenses not intended for overnight use. Annualized incidences per 10 000 contact lens users varied by type of contact lens from 0.62 to 2.52. Other studies looking at the incidence of contact lens‐related microbial keratitis describe ranges from 1.9 to 25.4 (Cheng et al., 1999; Poggio et al., 1989; Stapleton et al., 2008). These studies found considerably higher incidences of keratitis compared with the current study. The discrepancy is likely caused by the narrow inclusion criteria used in our study, where only patients requiring fortified antibiotics, and thus hospitalization, were included. Consequently, the incidences cannot be compared directly.

In previous studies on microbial keratitis, the authors often report a higher risk of keratitis in younger contact lens users. One study found a peak incidence of microbial keratitis at age 22 (Lam et al., 2002). In other articles, mean ages for microbial keratitis have been reported to be in the range of 22–35 years (Nilsson & Montan, 1994, p. 99; Keay et al., 2006; Uno et al., 2011; Hoddenbach et al., 2014; Lam et al., 2013; Rahimi et al., 2015). The patients in our study had a higher median age of 50 years. One possible explanation for this discrepancy might be that older patients with keratitis are more likely to develop a severe clinical course. Miedziak et al. (1999) examined all cases of microbial keratitis and found that higher age was a statistically significant risk factor for requiring penetrating keratoplasty. One reason for this might be that with increasing age, the capability of the immune system declines. Additionally, corneal sensitivity decreases with age, and infections might become more severe before presentation.

Nearly, all of the patients were experienced contact lens users, and a large majority had been using contact lenses for many years. One possible reason for this might be that after years of uneventful contact lens wear, contact lens users may become less diligent with hygiene, thus increasing their risk of keratitis. Contact lens users might also stop attending regular visits to opticians, opting instead to purchase lenses online.

When comparing the users of different types of contact lenses, the rates of improper use were similar, and the differences were not statistically significant. Using a narrow definition of the term (as defined in ‘Materials and Methods’), 45% of patients admitted improper use of their contact lenses. Other authors, using a wider definition, such as ever having showered or napped while wearing contact lenses, have found that around 99% of contact lens users report at least one contact lens hygiene risk behaviour (Cope et al., 2015).

We found that a low proportion of patients (37%) had knowledge of keratitis as a potential complication of contact lens use. In four of these 15 cases, the knowledge was a result of these patients having suffered from previous episodes of keratitis. This suggests that many patients acquire and use contact lenses without receiving or integrating information about the risk of potentially severe complications.

Several studies have shown that keratitis is more prevalent during summer (Gorski et al., 2016; Ting, Ho, Cairns, et al., 2021). In our study, the month with the most admissions was May. In addition to a peak in number of cases from May to July, there was a second peak from October to December (Figure 1). Other studies have reported similar findings. A study from Canada showed the onset of Acanthamoeba keratitis in the summer and fall (McAllum et al., 2009). Studies looking both at contact lens‐related keratitis and all forms of keratitis have found a higher incidence and proportion of P. aeruginosa keratitis in the summer (Gorski et al., 2016; Green et al., 2008; Ting, Ho, Deshmukh, et al., 2021) and increases in incidence during nonwinter months (Ni et al., 2015). This has led to several hypotheses, such as higher temperatures facilitating bacterial growth, increased outdoor activity, and increased contact with water during warmer months (Gorski et al., 2016; Ting, Ho, Cairns, et al., 2021).

FIGURE 1.

FIGURE 1

Open in a new tab

Chart illustrating the distribution of admissions by month. The number of patients admitted is in brackets.

Pseudomonas aeruginosa was the most frequently isolated microbe. This finding is consistent with similar studies (Fleiszig et al., 2020; Stapleton et al., 2022). The second most common microbe was Corynebacterium species. Corynebacterium macginleyi is a gram‐positive, lipophilic, facultatively anaerobic rod. It is a part of the conjunctival normal flora (Aoki et al. 2021). Due to its lipophilic nature, C. macginleyi is thought to thrive in the lipid‐rich environment of the ocular surface. It has a relative lack of virulence traits and is susceptible to most common antibiotics. Infection with C. macginleyi has been noted to often lead to uneventful courses of disease (Sagerfors et al., 2021). This is consistent with our finding that the ulcers caused by Corynebacterium spp. were smaller than those caused by other microbes.

Many studies on contact lens‐related keratitis are retrospective, with information obtained from hospital charts. A strength of the present study is that we prospectively interviewed patients during their hospital stay to obtain the best possible information regarding contact lens use and misuse and their knowledge about possible complications. Limitations include that we used a narrow definition of improper use of contact lenses. Risk factors such as showering while wearing contact lenses were not included, even though the literature shows that these activities cause an increased risk of keratitis (Stellwagen et al., 2020). Patients were included based on a subjective, clinical assessment of the severity of their keratitis, which may result in some uncertainty. As the patients were followed up by ophthalmologists outside our hospital, we have not been able to gather information about the patients' final visual acuity. Our study includes relatively few patients, and our findings would have been more reliable if more patients had been included. A completely accurate database of the number of people using different types of contact lenses does not exist in Norway. The data used is based on opticians voluntarily submitting data on their contact lens sales, which likely could affect the calculations of incidences of keratitis.

In conclusion, we have provided the annual incidence of severe contact lens‐related microbial keratitis in a Norwegian population for the first time. In our climate, the incidence seems to be highest in the spring and early summer months. The use of extended‐wear contact lenses intended for overnight use substantially increased the risk of keratitis. Most cases of severe keratitis occurred in middle‐aged persons that had used contact lenses for many years, and of whom the majority had no knowledge about keratitis as a potential complication. Better knowledge of microbial keratitis among patients and healthcare providers might decrease the number of infections that progress to a severe stage. Healthcare providers should inform users of contact lenses about the risk of keratitis and correct usage of contact lenses at every subsequent visit. There is reason to believe that a change in consumer behaviour to favour daily disposable contact lenses would result in a decrease in the incidence of severe contact lens‐related keratitis.

ACKNOWLEDGEMENTS

We are thankful to Ann Elisabeth Ystenæs, Synsinformasjon, and Kantar for information about contact lens use in Norway.

Sund, M.H. , Slettedal, J.K. , Sæthre, M. , Haslev, H.P. , Kristianslund, O. , Østern, A.E. et al. (2025) Incidence, risk factors, and patient characteristics in severe contact lens‐related microbial keratitis. Acta Ophthalmologica, 103, 289–294. Available from: 10.1111/aos.16796

REFERENCES

  1. Cheng, K.H. , Leung, S.L. , Hoekman, H.W. , Beekhuis, W.H. , Mulder, P.G.H. , Geerards, A.J.M. et al. (1999) Incidence of contact‐lens‐associated microbial keratitis and its related morbidity. Lancet (London, England), 354(9174), 181–185. Available from: 10.1016/S0140-6736(98)09385-4 [DOI] [PubMed] [Google Scholar]
  2. Cope, J.R. , Collier, S.A. , Rao, M.M. , Chalmers, R. , Mitchell, G.L. , Richdale, K. et al. (2015) Contact lens wearer demographics and risk behaviors for contact lens‐related eye infections—United States, 2014. MMWR. Morbidity and Mortality Weekly Report, 64(32), 865–870. Available from: 10.15585/mmwr.mm6432a2 [DOI] [PMC free article] [PubMed] [Google Scholar]
  3. Fleiszig, S. M. J. , Kroken A. R., Nieto V., Grosser M. R., Wan S. J., Metruccio M. M.E., Evans D. J. (2020). Contact lens‐related corneal infection: intrinsic resistance and its compromise. Progress in Retinal and Eye Research, 76, 100804. 10.1016/j.preteyeres.2019.100804 [DOI] [PMC free article] [PubMed] [Google Scholar]
  4. Gorski, M. , Genis, A. , Yushvayev, S. , Awwad, A. , Lazzaro D. R. (2016). Seasonal variation in the presentation of infectious keratitis. Eye & Contact Lens, 42(5), 295–297. 10.1097/ICL.0000000000000213 [DOI] [PubMed] [Google Scholar]
  5. Green, M. , Apel, A. & Stapleton, F. (2008) A longitudinal study of trends in keratitis in Australia. Cornea, 27(1), 33–39. Available from: 10.1097/ICO.0b013e318156cb1f [DOI] [PubMed] [Google Scholar]
  6. Hoddenbach, J.G. , Boekhoorn, S.S. , Wubbels, R. , Vreugdenhil, W. , van Rooij, J. & Geerards, A.J.M. (2014) Clinical presentation and morbidity of contact lens‐associated microbial keratitis: a retrospective study. Graefe's Archive for Clinical and Experimental Ophthalmology = Albrecht von Graefes Archiv Fur Klinische Und Experimentelle Ophthalmologie, 252(2), 299–306. Available from: 10.1007/s00417-013-2514-1 [DOI] [PubMed] [Google Scholar]
  7. Keay, L. , Edwards, K. , Naduvilath, T. , Forde, K. & Stapleton, F. (2006) Factors affecting the morbidity of contact lens‐related microbial keratitis: a population study. Investigative Ophthalmology & Visual Science, 47(10), 4302–4308. Available from: 10.1167/iovs.06-0564 [DOI] [PubMed] [Google Scholar]
  8. Lam, D.S. , Houang, E. , Fan, D.S. , Lyon, D. , Seal, D. , Wong, E. et al. (2002) Incidence and risk factors for microbial keratitis in Hong Kong: comparison with Europe and North America. Eye (London, England), 16(5), 608–618. Available from: 10.1038/sj.eye.6700151 [DOI] [PubMed] [Google Scholar]
  9. Lam, J.S. , Tan, G. , Tan, D.T. & Mehta, J.S. (2013) Demographics and behaviour of patients with contact lens‐related infectious keratitis in Singapore. Annals of the Academy of Medicine, Singapore, 42(10), 499–506. [PubMed] [Google Scholar]
  10. McAllum, P. , Bahar, I. , Kaiserman, I. , Srinivasan, S. , Slomovic, A. & Rootman, D. (2009) Temporal and seasonal trends in acanthamoeba keratitis. Cornea, 28(1), 7–10. Available from: 10.1097/ICO.0b013e318181a863 [DOI] [PubMed] [Google Scholar]
  11. Miedziak, A.I. , Miller, M.R. , Rapuano, C.J. , Laibson, P.R. & Cohen, E.J. (1999) Risk factors in microbial keratitis leading to penetrating keratoplasty. Ophthalmology, 106(6), 1166–1171. Available from: 10.1016/S0161-6420(99)90250-6 [DOI] [PubMed] [Google Scholar]
  12. Morgan, P. , Woods, C.A. , Tranoudis, I.G. , Helland, M. & Efron, N. (2020) International contact lens prescribing in 2019. Contact Lens Spectrum, 35, 26–32. [Google Scholar]
  13. Ni, N. , Nam, E.M. , Hammersmith, K.M. , Nagra, P.K. , Azari, A.A. , Leiby, B.E. et al. (2015) Seasonal, geographic, and antimicrobial resistance patterns in microbial keratitis: 4‐year experience in eastern Pennsylvania. Cornea, 34(3), 296–302. Available from: 10.1097/ICO.0000000000000352 [DOI] [PubMed] [Google Scholar]
  14. Nilsson, S.E. & Montan, P.G. (1994) The hospitalized cases of contact lens induced keratitis in Sweden and their relation to lens type and wear schedule: results of a three‐year retrospective study. The CLAO Journal: Official Publication of the Contact Lens Association of Ophthalmologists, Inc, 20(2), 97–101. [PubMed] [Google Scholar]
  15. Poggio, E.C. , Glynn, R.J. , Schein, O.D. , Seddon, J.M. , Shannon, M.J. , Scardino, V.A. et al. (1989) The incidence of ulcerative keratitis among users of daily‐wear and extended‐wear soft contact lenses. The New England Journal of Medicine, 321(12), 779–783. Available from: 10.1056/NEJM198909213211202 [DOI] [PubMed] [Google Scholar]
  16. Rahimi, F. , Hashemian, M.N. , Khosravi, A. , Moradi, G. & Bamdad, S. (2015) Bacterial keratitis in a tertiary eye centre in Iran: a retrospective study. Middle East African Journal of Ophthalmology, 22(2), 238–244. Available from: 10.4103/0974-9233.151870 [DOI] [PMC free article] [PubMed] [Google Scholar]
  17. Sagerfors, S. , Poehlein, A. , Afshar, M. , Lindblad, B.E. , Brüggemann, H. & Söderquist, B. (2021) Clinical and genomic features of Corynebacterium macginleyi‐associated infectious keratitis. Scientific Reports, 11, 6015. Available from: 10.1038/s41598-021-85336-w [DOI] [PMC free article] [PubMed] [Google Scholar]
  18. Statistics Norway . (2023) 07459: Alders‐ og kjønnsfordeling i kommuner, fylker og hele landets befolkning (K) 1986–2023. https://www.ssb.no/statbank/table/07459/ [Accessed: 30 May 2023].
  19. Stapleton, F. & Carnt, N. (2012) Contact lens‐related microbial keratitis: how have epidemiology and genetics helped us with pathogenesis and prophylaxis. Eye (London, England), 26(2), 185–193. Available from: 10.1038/eye.2011.288 [DOI] [PMC free article] [PubMed] [Google Scholar]
  20. Stapleton, F. , Keay, L. , Edwards, K. & Holden, B. (2013) The epidemiology of microbial keratitis with silicone hydrogel contact lenses. Eye & Contact Lens, 39(1), 79–85. Available from: 10.1097/ICL.0b013e3182713919 [DOI] [PubMed] [Google Scholar]
  21. Stapleton, F. , Keay, L. , Edwards, K. , Naduvilath, T. , Dart, J.K.G. , Brian, G. et al. (2008) The incidence of contact lens‐related microbial keratitis in Australia. Ophthalmology, 115(10), 1655–1662. Available from: 10.1016/j.ophtha.2008.04.002 [DOI] [PubMed] [Google Scholar]
  22. Stapleton, F. , Shrestha, G.S. , Vijay, A.K. & Carnt, N. (2022) Epidemiology, microbiology, and genetics of contact lens‐related and non‐contact lens‐related infectious keratitis. Eye & Contact Lens, 48(3), 127–133. Available from: 10.1097/ICL.0000000000000884 [DOI] [PubMed] [Google Scholar]
  23. Stellwagen, A. , MacGregor, C. , Kung, R. , Konstantopoulos, A. & Hossain, P. (2020) Personal hygiene risk factors for contact lens‐related microbial keratitis. BMJ Open Ophthalmology, 5(1), e000476. Available from: 10.1136/bmjophth-2020-000476 [DOI] [PMC free article] [PubMed] [Google Scholar]
  24. Ting, D.S.J. , Ho, C.S. , Cairns, J. , Gopal, B.P. , Elsahn, A. , al‐Aqaba, M. et al. (2021) Seasonal patterns of incidence, demographic factors and microbiological profiles of infectious keratitis: the Nottingham infectious keratitis study. Eye (London, England), 35(9), 2543–2549. Available from: 10.1038/s41433-020-01272-5 [DOI] [PMC free article] [PubMed] [Google Scholar]
  25. Ting, D.S.J. , Ho, C.S. , Deshmukh, R. , Said, D.G. & Dua, H.S. (2021) Infectious keratitis: an update on epidemiology, causative microorganisms, risk factors, and antimicrobial resistance. Eye (London, England), 35(4), 1084–1101. Available from: 10.1038/s41433-020-01339-3 [DOI] [PMC free article] [PubMed] [Google Scholar]
  26. Uno, T. , Fukuda, M. , Ohashi, Y. , Shimomura, Y. , Ishibashi, Y. , Inaba, M. et al. (2011) Survey of severe contact lens‐associated microbial keratitis in Japan. Nippon Ganka Gakkai Zasshi, 115(2), 107–115. [PubMed] [Google Scholar]
  27. Zimmerman, A.B. , Nixon, A.D. & Rueff, E.M. (2016) Contact lens associated microbial keratitis: practical considerations for the optometrist. Clinical Optometry, 8, 1–12. Available from: 10.2147/OPTO.S66424 [DOI] [PMC free article] [PubMed] [Google Scholar]

Articles from Acta Ophthalmologica are provided here courtesy of Wiley

RESOURCES