What is ortho-k?

• Ortho-k is short for orthokeratology. 
• Ortho-k lenses are worn during sleep to gently reshape the cornea so you can see clearly during the day without the need for glasses or contact lenses.
• Correction from ortho-k is temporary and requires ongoing overnight wear to maintain.
• To achieve a successful lens fit, ortho-k typically require more appointments than soft contact lenses.
• For new wearers, ortho-k is typically less comfortable than soft contact lenses, but comfort usually improves dramatically within the first week. 
• Ortho-k is safe to wear as long as lens wear and care guidelines are followed, and ongoing follow-up care visits are attended.

In many ways the eye works like a camera. It has two lenses that focus light but instead of focusing light onto a computer chip or film, light is instead focused onto the retina.

The main focusing lens is the cornea at the front of the eye, which has a fixed focus strength and provides around 75% of the eye's focus power.

The lens inside the eye makes up the difference and is flexible to allow change of focus to different distances - it is the lens inside your eye that changes to keep objects in focus as they are moved closer to you.

Ortho-k lenses correct myopia by gently and temporarily flattening the cornea by a small amount that is matched to the amount of myopia to correct, with higher amounts of myopia needing more corneal flattening.¹

Flattening the cornea has the effect of reducing the focussing power of the cornea, and because myopia is in effect caused by the focussing power of the eye being too strong, this has the effect of neutralizing the myopia and bringing objects back into focus on the retina.

Ortho-k lenses are worn overnight, which is when the flattening effect takes place, and removed during the day with the now flattened corneal profile temporarily fixing the myopia and providing clear vision.

Corneal flattening from ortho-k is not permanent and most of its effect will wear off over the first few days after lens wear is stopped.⁵ The reason for this is because ortho-k mainly affects the front most surface of the cornea.⁶ This front surface layer is gently compressed in some places and expands in others to match the profile of the ortho-k lens. When lens wear is stopped the cornea gradually returns to its natural state from before ortho-k was started.¹ 

An analogy that might be easier to visualize is to imagine sitting in the same position on a couch for the whole night - when you get up you will leave your imprint in the couch cushion, which will gradually bounce back during the day. If you were to sit in the same spot night after night the impression would become stronger and last longer - in ortho-k this is why it typically takes up to 1-week of overnight wear to achieve the full effect⁷ - but even with repeated sitting on the couch overnight, the impression will still gradually bounce back after you get up.

The temporary effect from ortho-k offers some useful advantages when compared to the more permanent option of laser surgery which removes tissue from the cornea. Ortho-k can be stopped at any time to allow the eye to return to its original shape. In fact research reveals that most of the ortho-k effect to be reversed within the first week of stopping lens wear.⁵ For children the temporary effect allows flexibility to adapt the ortho-k lens design as their eyes continue to grow and change.    

Myopia, also known as near or short sight, is becoming increasingly common in children, which if allowed to progress can lead to long-lasting and detrimental effects on vision and eye health in adulthood.

Fortunately, there is a lot that can be done to help slow myopia progression in children, including prescribing special types of spectacles or contact lenses, and promoting good habits like reduced time on close work and more outdoor time.

When it comes to myopia control treatments, ortho-k has been shown to slow progression of myopia in children by about a half, and currently has the most research supporting its myopia control characteristics than other myopia control methods.^2,3,8

Specialized equipment and expertise is required to achieve successful ortho-k lens fit. In most countries this would be conducted by an optometrist or eye doctor.

To assess suitability for ortho-k both refraction (eye prescription) and the shape profile of the cornea (the clear dome at the front of the eye) needs to be measured. Corneal shape is measured using an instrument called a corneal topographer, that takes a photograph of a light pattern reflected onto the eye. Computer software then processes the photograph to build a simulated 3-dimensional model of the cornea.⁹

The computer model of the cornea is used to calculate the best fit ortho-k lens. For some ortho-k designs the eye doctor will select a pre-made lens that best fits the model. For other ortho-k lens designs the computer model is entered into different computer software that designs a custom ortho-k lens that needs to be made especially for you.

Regardless of the ortho-k design that is used, the tried and tested lens selection and design process will likely result in an ortho-k lens that will fit extremely well to the eye - like a custom made suit. This measurement and modelling process is so reliable that it's generally at this stage, before a lens is even put on the eye, that an eye doctor is able to tell you if ortho-k is likely to work.

If shown to be suitable you should be advised of the steps that need to be followed to complete the lens fit process. It generally takes more visits to fit ortho-k compared to standard daily soft contact lenses, mostly because ortho-k lenses are custom designed for each individual case.^1,9

While the number of visits that are required to achieve successful ortho-k lens fit can vary widely depending refraction and cornea shape, a typical visit schedule will be:

1. Refraction and eye measurements - these will be used to order the lens.
2. Lens collection visit to be shown how to apply, remove and care for ortho-k lenses.
3. Morning visit after the first night of lens wear - this visit is to ensure that overnight lens wear has been successful, and to reinforce lens handling advice. Early indication of lens fit success can sometimes be assessed, though full effect shouldn't be expected until 1-week of overnight lens wear.
4. Morning visit after around 1-week of overnight lens wear - this is when the full effect can be expected and the optometrist / eye doctor able to assess if lens fit needs to be altered. In some cases it can take longer to achieve full effect so you shouldn't be surprised if the full effect has not been achieved at this visit.

Ongoing visits will depend on whether or not the lens needs to be altered to improve fit. It is important to understand that ortho-k lenses are custom designed and lens wear is needed to fully understand how an individual eye will respond to ortho-k lens wear.

In some cases the optometrist / eye doctor will want to continue wear for a few more nights before deciding if a good lens fit has been achieved. In other cases they might decide to order a slight variation in lens design to improve fit. Either way ongoing appointments will start to spread out once optimal lens fit is achieved.

It’s understandable to think that molding the shape of the eye is going to hurt, but in reality, despite the eye being extremely sensitive, this is not generally the case.

You’ve just read that ortho-k lenses are either custom-made for an individual eye, or selected to very closely match the contours of the eye. This close alignment removes most of the discomfort that could otherwise occur, however, for anyone new to ortho-k, there is still the initial sensation of having something in your eye like a piece of dust. This is simply due to the top eyelid feeling and highlighting the presence of the lens on the eye.

Typically the eye will create tears to try and wash the ortho-k lens out because it thinks it’s like a piece of dust. Over a short period of time this usually settles down to the point where the lenses can be as comfortable as to not be felt in the eye at all.

Another analogy, but different to the previous cushion analogy, is to think of the ortho-k lens as being like a new pair of shoes that are at first uncomfortable but soon become comfortable after a few days of wear.   

All contact lenses can increase risk of infection as a result of the lens being placed on your eye. Ortho-k lenses introduce an extra risk from being worn during sleep when the eyes are closed, although they are safer to sleep in than soft contact lenses.^10-12 Blinking is a natural cleaning and defense mechanism for eyes, and the eye not blinking during sleep reduces the effectiveness of this defense mechanism.

The good news is that risk from infection can be greatly reduced if proper cleaning steps are followed, and also to avoid the lenses and their cases coming into contact with tap water. This last point is so important that it’s worth repeating - tap water should never be allowed to come in contact with contact lenses, including ortho-k, and any devices used with contact lenses, such as cases or lens application holders.

In many ways ortho-k lenses can be considered one of the easiest types of contact lenses to wear. Being made from a rigid material can make them easier to pick up and handle compared to floppier soft contact lenses.

Ortho-k lenses are also smaller than most soft contact lenses, which can make them easier to apply to the eye. Their smaller size can make them a little harder to remove than soft lenses, but there are easily learned lens removal techniques to simplify this process.

Being worn overnight also offers advantages, because once applied the wearer closes their eyes and goes to sleep, which removes the problem of a lens falling out during the day.

Although ortho-k is most commonly prescribed to correct myopia (short-sightedness), it can also be used to correct hyperopia (long-sightedness), astigmatism and presbyopia (blurred near vision that commences when we reach our 40s).¹

For myopia, up to -4.50D of myopia with up to -1.50D of astigmatism is generally recognized as falling well within the acceptable range of correction using ortho-k. This is backed up by medical approvals, like the USA Food and Drug Administration (FDA) providing licensing for this range.¹

Higher myopia correction can be achieved from ortho-k,¹³ however likelihood of achieving a successful outcome diminishes towards higher amounts of myopia. It must be recognized that successful vision correction from ortho-k is dependent on individual characteristics.

For these reasons any published suitability range should only be considered a guide, and an optometrist or eye doctor consulted for advice on your or your child's suitability for ortho-k.  

Read more about the benefits and suitability of ortho-k for the following age groups:

• Ortho-k for children
• Ortho-k for teenagers
• Ortho-k for young adults

The answer to this question depends on motivation, individual circumstances and cost.

Many people are very happy wearing ortho-k lenses, and as described above they can offer great benefits for slowing progression of myopia in children. However, motivation is needed to get through the first few weeks, as it typically takes more time to fit ortho-k compared to soft contact lenses and they are less comfortable over the first few times they are worn.

Once the new wearer has quickly adapted, though, research has indicated that some people who have experienced dry eye symptoms in soft contact lens wear can actually find ortho-k a more comfortable way to correct their vision - with their dry eye symptoms improving and these wearers preferring ortho-k.¹⁴

There is typically a higher upfront cost for ortho-k compared to daily wear contact lenses, because of the greater amount of consultation time that is generally required and higher individual lens cost. However, ortho-k lenses last longer than disposable contact lenses causing the cost to likely balance out over time.

How your optometrist / eye doctor charges for these costs depends greatly not only how they choose to run their practice, but also by country and region. Some countries favour direct debit systems, resulting in eye care practices spreading cost in monthly direct debits. In most other cases they will either ask for the full or partial cost to be paid once ortho-k has been shown to be suitable option, with the remaining balance payable once successful lens fit has been achieved.

Once cost is factored into your decision, the next question becomes preference. Ortho-k lenses are particularly suitable for active people who are inconvenienced by wearing contact lenses during the day, and in some cases can be a more comfortable option for those who find daytime contact lens wear uncomfortable.¹⁴

In children, parents often like the control that ortho-k provides because lens wear and care happens entirely within the house.¹  

To ensure correct fitting and that your or your child’s eyes are suitable, ortho-k lenses should only be purchased from an optometrist or eye doctor. Specialist equipment is needed to measure the eye to calculate lens fit, and to assess the effects of ortho-k lens wear over time. The lens design complexity and need for ongoing assessment with ortho-k wear makes supply through the internet impractical.

Depending on location, fitting fees and ongoing follow-up after care may be bundled with lens price, or charged separately, which can make it difficult to compare prices across different providers. Experience is probably the most important guide - an experienced ortho-k lens fitter may be willing to offer a suitability assessment before asking for commitment to purchase lenses. 

The following websites provide listings of ortho-k lens fitting optometrists.

• Global: https://www.ortho-kacademy.com/find-an-ortho-k-doctor2/
• Australia/NZ: http://www.oso.net.au/where-do-i-get-it
• Europe: https://www.eurok.eu/practitioners

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2. Si JK, Tang K, Bi HS, Guo DD, Guo JG, Wang XR. Orthokeratology for myopia control: a meta-analysis. Optom Vis Sci. 2015 Mar;92(3):252-7. [link]
3. Sun Y, Xu F, Zhang T, Liu M, Wang D, Chen Y, Liu Q. Orthokeratology to control myopia progression: a meta-analysis. PLoS One. 2015 Apr 9;10(4):e0124535. [link]
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8. Brennan NA, Toubouti YM, Cheng X, Bullimore MA. Efficacy in myopia control. Prog Retin Eye Res. 2021 Jul;83:100923. (link)
9. Cho P, Cheung SW, Mountford J, White P. Good clinical practice in orthokeratology. Cont Lens Anterior Eye. 2008 Feb;31(1):17-28. 
10. Bullimore MA, Sinnott LT, Jones-Jordan LA. The risk of microbial keratitis with overnight corneal reshaping lenses. Optom Vis Sci 2013;90:937-944.
11. 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.
12. 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. 
13. Charm J, Cho P. High myopia-partial reduction ortho-k: a 2-year randomized study. Optom Vis Sci. 2013 Jun;90(6):530-9. (link)
14. Duong K, McGwin G Jr, Franklin QX, Cox J, Pucker AD. Treating Uncomfortable Contact Lens Wear With Orthokeratology. Eye Contact Lens. 2021 Feb 1;47(2):74-80.