Are ortho-k lenses safe?

• All contact lenses can increase risk of eye infection, but the risk is low with proper lens hygiene processes
• The risk of eye infection from ortho-k is around 1 case per 1,000 to 2,000 wearers per year
• Ortho-k has a similar safety profile to wearing daytime reusable soft contact lenses, although ortho-k is safer to wear overnight (while sleeping) than soft contact lenses.
• To enhance safety, ortho-k lenses should only be fit by an experienced optometrist or eye doctor.
• Tap water should never come into contact with contact lenses, contact lens cases and other accessories as it dramatically increases the risk of serious eye infection.

Ortho-k is a special type of rigid contact lens which is worn overnight while sleeping, to gently reshape the cornea (the clear dome at the front of the eye) so that daytime wear of glasses or contact lenses is not needed.¹

At the turn of the century, a flurry of case reports were published that suggested a higher than expected rate of eye infection in children wearing ortho-k. However, researchers found that most of these cases occurred in East Asia and were found to be due to unsafe practices, particularly poor regulation in ortho-k lens fitting, and using tap water as a cleaning solution. Having realized the problem, local governments stepped in to closely regulate ortho-k lens cleaning solutions, and who could fit ortho-k lenses.²

Two large studies have since been published in 2013 and 2021 which revealed a strong safety profile for ortho-k.^3,4 Including comparison to people who don't wear contact lenses⁵ and to soft contact lenses,⁶ the risk of an eye infection is:

• 1 case per 7,000 people per year who don't wear contact lenses
• 1 case per 1,000 to 2,000 wearers per year with ortho-k
• 1 case per 1,000 wearers per year with reusable soft contact lenses
• 1 case per 5,000 wearers per year with daily disposable soft contact lenses

An important learning from these problems with ortho-k in the early 2000's was that for best safety outcomes, ortho-k lenses should only be fit by an experienced and appropriately qualified optometrist or eye doctor.²

In fact, one study which observed all young patients (up to 16 years of age) who wore ortho-k in a single expert clinic showed that there were no cases of corneal infection (microbial keratitis) over 10 years of follow up.⁷

These types of contact lenses are quite different: ortho-k lenses are worn overnight and soft lenses are typically worn only during the day. Daily disposable soft contact lenses are applied from a sterile container, worn only once and discarded at the end of the day. Reusable soft contact lenses are worn during the day, then cleaned and stored overnight and used again for two to four weeks.

Ortho-k lenses, by comparison, can last for 6 to 12 months or longer. They require daily cleaning and storage of the same lenses. For both ortho-k and reusable soft contact lenses, the extra stages in the lens wear process create greater chances for a germ to come into contact with the lens, through hands or other cleaning accessories. Their safety profile appears to be similar.

Note that sleeping in soft contact lenses overnight appears to be riskier than sleeping in ortho-k lenses overnight. This is likely because ortho-k lenses are removed during the day giving the eye some time without lenses. When soft lenses are worn overnight they are typically worn on an extended wear basis resulting in the same lens remaining on the eye for many days. Eye care practitioners would rarely recommend this pattern of wear to children and young people, except in special circumstances.

In a direct comparison, daily disposable soft lenses have the smallest risk of eye infection followed by ortho-k and daily wear reusable soft lenses which are similar. Overnight wear of soft contact lenses is the most risky wearing pattern.^3,4,6

Overall, the risk of eye infection from contact lenses and ortho-k is extremely low if they are worn and cared for properly.

An adverse event can be anything that impacts contact lens wear, from a mild annoyance to the most serious, a corneal infection. Over 10 years of wear commencing in childhood, ortho-k shows a similar rate of adverse events to soft contact lenses. For both contact lens types, the adverse events were mild and the risks were very low.⁸

The most common mild adverse event in both ortho-k and soft contact lens wear is allergic conjunctivitis, which can be associated with hayfever. This occurred in around 4% of wearers, per year. Around 10% of wearers experienced some adverse event over this 10 year duration of contact lens wear, but these were mostly mild issues of conjunctivitis and corneal surface irritation, which rarely affected lens wear.⁸

The good news is that risk from infection can be greatly reduced if proper cleaning steps are followed, and also by ensuring that the ortho-k lenses, their case and any other lens accessories avoid coming into contact with tap water.^1,7

Why avoid tap water? Because a water born organism called acanthoemeba is often found in water, particularly in water storage tanks and tap water. Acanthoemeba doesn't in general cause us humans any problems, except if it gets into the cornea when it can cause serious eye infection, which can become sight threatening if not treated.⁷

Fortunately, the eye is highly resilient to acanthoemeba, and because of the eyes' strong defense system, infection is extremely rare. Any contact lens wear including ortho-k increases risk of acanthoemeba infection because of the potential to bring water into prolonged contact with the eye.⁷ Unfortunately, in the rare cases of eye infection in ortho-k, acanthamoeba is the cause around one-third of the time.⁹

The prescribing eye doctor should advise how to clean and look after contact lenses, and should be contacted for advice if you are in any way unsure how to care for ortho-k lenses.

You should be aware that all contact lenses, including ortho-k, can increase risk of an eye infection purely as a result of the lens being placed on your eye, and from your hands being in closer contact with your eyelids and eye surface via the contact lens.

However, research shows that ortho-k lenses are generally safe to wear when they are fit by an experienced optometrist or eye doctor, and as long as lens care and cleaning steps are followed.

1. Vincent SJ, Cho P, Chan KY, Fadel D, Ghorbani-Mojarrad N, González-Méijome JM, Johnson L, Kang P, Michaud L, Simard P, Jones L. CLEAR - Orthokeratology. Cont Lens Anterior Eye. 2021 Apr;44(2):240-269. (link)
2. Liu YM, Xie P. The Safety of Orthokeratology--A Systematic Review. Eye Contact Lens. 2016 Jan;42(1):35-42.
3. Bullimore MA, Sinnott LT, Jones-Jordan LA. The risk of microbial keratitis with overnight corneal reshaping lenses. Optom Vis Sci 2013;90:937-944.
4. 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.
5. Jeng BH, Gritz DC, Kumar AB, Holsclaw DS, Porco TC, Smith SD, Whitcher JP, Margolis TP, Wong IG. Epidemiology of ulcerative keratitis in Northern California. Arch Ophthalmol. 2010 Aug;128(8):1022-8. 
6. Stapleton F, Keay L, Edwards K, Naduvilath T, Dart JK, Brian G, Holden BA. The incidence of contact lens-related microbial keratitis in Australia. Ophthalmology. 2008 Oct;115(10):1655-62.
7. Ibrahim YW, Boase DL, Cree IA. How Could Contact Lens Wearers Be at Risk of Acanthamoeba Infection? A Review. J Optom. 2009;2(2):60–6.
8. 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 May;38(3):281-289. 
9. Kam KW, Yung W, Li GKH, Chen LJ, Young AL. Infectious keratitis and orthokeratology lens use: a systematic review. Infection. 2017 Dec;45(6):727-735.