How can we best promote safety in orthokeratology (OK) wear? Many OK lens related incidents are due to poor lens handling and hygiene processes.1 Here is a case described by PC of a child who suffered microbial keratitis, which, on questioning, appeared to be associated with inappropriate OK lens care.
Ensuring compliance in OK wear
Poor compliance with contact lens hygiene processes can lead to OK lens-related infections.1 The main reasons for poor compliance consist of lack of knowledge for procedures and the potential consequences of non-compliance.2
Surveys have shown that the full OK lens compliance rate in young wearers was 23% in Taiwan3 and 14% in China.4 In Taiwan, a highly educated parent group were surveyed who were mostly myopic themselves. Their children were all 6-13 years of age and parents took responsibility for lens hygiene processes. Compliance was uniformly reported as high for lens and lens accessory cleaning processes, and was highest in newer wearers (less than 6 months). Lowest compliance rates were for "intensive care for lenses (removing lens protein deposition)".3
In China, children who had worn OK for at least one year were surveyed. The most common areas of non-compliance were exposure to nonsterile solution (eg. water, from not drying hands properly), not removing lens depositions according to the eye care practitioners' (ECPs) recommendations and inadequate hand washing.4
Children undertaking lens care themselves were less compliant than children whose lens care was supervised or undertaken by their parents.4 Another study of long-term OK wearers with an average age of 12.7 years found a higher microbial bioburden of the OK care system in male participants.5 Reinforcement of the lens cleaning process is important for all patients - especially for children undertaking lens care themselves and young male wearers. Explanations that include the reasoning behind each step could strengthen the patient’s attitude towards the importance of being compliant.2
The community also shared some tips on improving compliance. As the lens care procedures may appear complicated to the parents and wearer, a printed handout with pictorial references can be useful for patients to remember the instructions.
Rubbing OK lenses whilst cleaning improves removal of depositing6 and additional protein removal cleaner removes further depositing and biofilm from gas permeable lenses better than the routine cleaning solution alone.7 This should be an important part of OK lens cleaning procedures.
What about lens cases? A study of almost 200 asymptomatic OK patients aged 7 to 17 years attending a hospital clinic in China investigated lens case hygiene processes and collected cases for analysis. The least contamination was found with when lens cases were rinsed with multipurpose solution and wiped with a tissue daily, and replaced every month. Cylindrical lens cases were less contaminated than flat lens case types.8
Key message: no water near lenses!
A key factor which may compromise the safety of OK lens wear is exposure to tap water - the most common risk factor for Acanthamoeba keratitis,9,10 which unfortunately makes up over one-third of all cases of OK-related microbial keratitis.11
Exposure can occur regularly when the wearer doesn't thoroughly dry their hands after washing, or rinses the contact lens, case or accessories with water. An example of this is described in a case study of severe Acanthamoeba infection, where the patient cleaned his lenses as instructed, but then rinsed and stored his lenses in tap water, and didn't clean or replace the lens case. The authors concluded that "heightened scrutiny [of lens hygiene] is critically important in orthokeratology rigid lens wear, especially in children".12
Regular follow up is crucial
Follow up is essential for the practitioner to monitor treatment outcomes as well as to examine eye health, regularly replace lenses and review lens care procedures. Jun et al showed that the rate of compliance with follow up appointments in China reduced from close to 100% in the first 3 months to around 85% after 6-9 months.4
It has been found that the average duration of wearing time before a case of microbial keratitis is 19 months.11 This indicates the importance of explaining the reasons for follow up and establishing patient education and practice procedures to ensure adherence.
How safe is orthokeratology?
The risk of microbial keratitis in childhood ortho-k wear is between 5 and 14 per 10,000 patient-wearing years.13,14
Data gathered from almost 200 ECPs in the United States for clinical care between 2004 and 2006 representing 677 children with 1435 patient-years of wear estimated the first incidence rate of 13.9 per 10,000 patient years of wear.13 The second, lower figure was from a recent study surveying a group of ophthalmology and optometry practices in Moscow, Russia, representing care occurring between 2010 and 2018 and just over 1000 records analyzed. The incidence in this newer study was estimated to be between 4.9 and 5.3 per 10,000 patient years of wear.14
The improved safety profile in this recent study could reflect the impact of gathering data from a single group of practices with standardized training, whereas the previous study obtained data from numerous different practices. It could also reflect a concerted effort to improve ortho-k safety and compliance in the years since the significant concerns about infection were raised in the early 21st Century.1
Another study reviewed the ocular health of 489 OK-wearing eyes in 260 patients presenting consecutively over one year (2016) in China. Children were 8-15 years old with a mean refraction of -3.2D. There were no cases of microbial keratitis, 5 cases (1%) of corneal infiltrates and 29 cases (6%) with corneal staining of at least Grade 3. Interestingly, 14% had allergic conjunctivitis which increased the likelihood of Grade 2 or less corneal staining by 1.7 times, but did not increase the risk of corneal infiltrates or Grade 3+ staining.15
Finally, a study which evaluated 10 years (2002 to 2012) of OK versus soft contact lens wear in children, in a single clinical setting, found no cases of microbial keratitis and no difference in adverse event rates between lens types, with a rate of 0.1% per year for corneal erosion and 3.5% per year for superficial punctate keratopathy, which was the most frequent adverse event. All adverse events resolved with short-term discontinuation of lens wear and/or application of topical drops or medications as required, and all patients resumed OK lens wear after resolution, indicating "the acceptable safety of OK treatment over long periods of lens wear."16
Take home messages:
- When cared for properly, OK lenses are a safe and effective option for myopic children.
- Many OK-related adverse events are due to improper lens care procedures. In addition, longer wearing time is associated with decreased compliance and increased risk of an adverse event. This means that the safety of OK can be promoted with proper parent and wearer education on hygiene and lens care procedures, plus reinforced explanations and adherence to regular follow up.
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- Liu YM, Xie P. The Safety of Orthokeratology--A Systematic Review. Eye Contact Lens. 2016 Jan;42(1):35-42. (link)
- McMonnies CW. Improving contact lens compliance by explaining the benefits of compliant procedures. Contact Lens Anterior Eye. 2011 Oct 1;34(5):249-52. (link)
- Chang LC, Sun CC, Liao LL. Compliance with orthokeratology care among parents of young children in Taiwan. Contact Lens Anterior Eye 2021 Feb 20:101427. (link)
- Jun J, Zhiwen B, Feifu W, Lili L, Fan L. Level of compliance in orthokeratology. Eye Contact Lens. 2018 Sep;44(5):330. (link)
- Lo J, Kuo MT, Chien CC, Tseng SL, Lai YH, Fang PC. Microbial bioburden of orthokeratology contact lens care system. Eye Contact Lens. 2016 Jan 1;42(1):61-7. (link)
- Cho P, Poon HY, Chen CC, Yuon LT. To rub or not to rub? - effective rigid contact lens cleaning. Ophthalmic Physiol Opt. 2020;40(1):17-23
- Nomachi M, Mori O, Imayasu M, Cavanagh H. Efficacy of Progent system against protein deposits and Staphylococcus epidermidis biofilm, isolated from contact-lens users. Optom Vis Sci 2014:Abstract 145173.
- Wang J, Liu L, Boost M, Yap M, Cho P. Risk factors associated with contamination of orthokeratology lens cases. Cont Lens Anterior Eye. 2020 Apr;43(2):178-184. (link)
- Wu J, Xie H. Orthokeratology lens-related Acanthamoeba keratitis: case report and analytical review. J Int Med Res. 2021 Mar;49(3):03000605211000985. (link)
- Zimmerman AB, Richdale K, Mitchell GL, Kinoshita BT, Lam DY, Wagner H, Sorbara L, Chalmers RL, Collier SA, Cope JR, Rao MM. Water exposure is a common risk behavior among soft and gas-permeable contact lens wearers. Cornea. 2017 Aug;36(8):995. (link)
- Kam KW, Yung W, Li GKH, Chen LJ, Young AL. Infectious keratitis and orthokeratology lens use: a systematic review. Infection. 2017;45(6):727-735. (link)
- Robertson DM, McCulley JP, Cavanagh HD. Severe acanthamoeba keratitis after overnight orthokeratology. Eye Contact Lens. 2007 May 1;33(3):121-3. (link)
- Bullimore MA, Sinnott LT, Jones-Jordan LA. The risk of microbial keratitis with overnight corneal reshaping lenses. Optom Vis Sci 2013;90:937-944. (link)
- Bullimore MA, Mirsayafov DS, Khurai AR, Kononov LB, Asatrian SP, Shmakov AN, Richdale K, Gorev VV. Pediatric Microbial Keratitis With Overnight Orthokeratology in Russia. Eye Contact Lens. 2021 Jul 1;47(7):420-425. (link)
- Hu P, Zhao Y, Chen D, Ni H. The safety of orthokeratology in myopic children and analysis of related factors. Contact Lens Anterior Eye. 2021 Feb 1;44(1):89-93. (link)
- Hiraoka T, Sekine Y, Okamoto F, Mihashi T, Oshika T. Safety and efficacy following 10-years of overnight orthokeratology for myopia control. Ophthalmic Physiol Opt. 2018;38(3):281-289. (link)