Myopia Profile


How much orthokeratology over-correction is ideal?

Posted on November 16th 2020 by Connie Gan

Sponsored by


PC posed a question regarding the acceptable amount of over-correction to incorporate in an OrthoK prescription to allow for good end-of-day vision in this post. Here’s what the community said:

PC With OrthoK fitting, what do people think is the appropriate level of over-correction to target, in view of providing optimal myopia control? Slight over-correction with OrthoK is expected to maintain clear vision from morning to night and to lessen day to day vision variability, but how much is too much? Haven’t found much on this in the literature.PP I’ve been using around 0.75DJK ... whatever leaves you with reasonable vision at the end of the day. So probably around +1.00 - +0.50 in the morning.AD There's no reason to overcorrect more than necessary, besides helping to cope with a little Exo and high AC/A. So we measure overrefraction after 4 Weeks in the morning and evening, project that degress to the end of the day...PC The reason for this question is that I wonder if correcting more than necessary has any detrimental effect for myopia control. Some patients might desire to wear their lenses every 2nd day, which to achieve means overcorrecting significantly on the 1st day to avoid blur on the 2nd. PP Some corneas “rebound” faster than others (hysteresis?) Also, it depends on the age and starting prescription they present in the beginning. Also, some are more sensitive to “blur.”CH I use +2 D Jesson Factors for most of my kids often combined with 1.4 positive E in the BC...And in only a handful of cases do I add VT or pull back the Jesson factor due to accommodation or convergence issues.TP I have found that many patients are satisfied without overcorrection even if there is around - 0,25 in the evening...RH My understanding is you ideally want a refraction-over-lens of plano if you want to optimize myopia control, as overminusing may introduce relatively more peripheral hyperopic defocus...HO some fitting guides recommend OR of +.50RH We do myopia control mostly with young kids, starting from 8-9 year old. We don't overcorrect them, they won't suffer from not maintaining clear vision during the day because most of them won't go to bed that late... Grownup in OrthoK might complain earlier but only in higher myopic powersDS I don’t think that the degree of foveal over-correction has any significant effect on the potential for myopia control. That portion of the orthokeratology is more related to the capacity to maintain reasonable visual acuity over a diurnal cycle.DS 0.50D

What are the considerations?

Reasons for over-correcting:

  • General consensus was to over-correct by 0.50D to 1.00D. However, this number may vary between patients, depending on how fast a cornea ‘rebounds’.
  • Sometimes, over-correcting may help in a person with high exophoria or AC/A ratio
  • One can consider measuring over-refraction after 4 weeks of wear in the morning and evening to work out the perfect over-correction
  • Some kids may prefer to wear the lenses every 2nd night but that may mean significant over-correction
  • Some may be more sensitive to blur than others so over-correction will help guarantee clear end-of-day vision.

Reasons for not over-correcting:

  • May not be particularly necessary as any blur at the end of the day is minimal, especially since younger kids will tend to have shorter waking hours (earlier bedtimes) than for the same consideration in adults
  • A plano over-refraction may be ideal, in the case that too much over-correction (manifest hyperopia) could potentially reduce the relative peripheral myopia desired from OrthoK treatment.

What the research tells us:

  • Mountford et al1 showed that the degree of regression during day-time hours is about 0.50-0.75D on average after 90 days of wear.
  • However, Chan et al2 showed that the conventional 0.75D over-correction was insufficient for full myopia correction to last through the day for some patients.
  • Gardiner et al3 showed that the amount of regression increases with higher amounts of baseline myopia. For example, a -4.00D myope regresses by about 1.00D at the end of the day on average.
  • Lau et al4 hypothesised that a higher amount of over-correction (study was up to 1.75D) may actually potentially improve the myopia control effect due to increased amounts of high order aberrations (HOAs) that have been suggested to play a part in reduction of axial elongation.5 However, increased HOAs may lead to poor low-light visual performance.
  • A clinical trial was completed in late 2019 which investigated OK fitting with a 'conventional compression factor' (0.50-0.75D over-correction target) compared to a matched group wearing OK with an 'increased compression factor' (1.50-1.75D over-correction target). The intended outcome was to measure any difference in myopia correction and control effects between the two lens fitting approaches. So far, preliminary findings have been reported indicating that the increased compression factor of 1D achieved around 0.30D additional refractive correction on average, after one month of wear, but unaided VA results were not significantly different between the groups.6 Any relationship to the myopia control effect will likely be reported in future.
  • There have been no studies equating the amount of over-correction in OrthoK with the shift in peripheral refraction, and how this relates to myopia control efficacy. While it makes logical sense that too much over-correction could influence the optics of OrthoK, until we understand more about how this could relate to the myopia control effect, the main concern is to ensure good vision for our OK wearing patients throughout the day. This includes good vision at near, which could potentially be influenced by too much over-correction (manifest hyperopia).

Take home messages:

  • Most contact lens companies already include approximately 0.50-0.75D of over-correction to account for regression during the day and this may be sufficient for most patients. For patients who do not reach full correction, an 'increased compression factor', or targeted higher over-correction, will be required.
  • It is prudent to check the patient’s end-of-day over-refraction after 4 weeks of wear, as it will give you a better idea of the patient’s level of vision at that time and adjustments can be made if they are bothered by poor end-of-day vision.
  • Incorporating a larger amount of over-correction than the lab’s standard 0.50-0.75D still remains a valid option to ensure good end-of-day acuity, provided it isn't too much to affect comfortable near vision.
  • The relationship between over-correction and OrthoK's myopia control effect has not yet been established, but a clinical trial completed in late 2019 may soon provide data on this question.

Meet the Authors:

About Connie Gan

Connie is a clinical optometrist from Kedah, Malaysia, who provides comprehensive vision care for children and runs the myopia management service in her clinical practice.

Read Connie's work in many of the case studies published on Connie also manages our Myopia Profile and My Kids Vision Instagram and My Kids Vision Facebook platforms.

About Kimberley Ngu

Kimberley is a clinical optometrist from Perth, Australia, with experience in patient education programs, having practiced in both Australia and Singapore.

Read Kimberley's work in many of the case studies published on Kimberley also manages our Myopia Profile and My Kids Vision Instagram and My Kids Vision Facebook platforms.

This content is brought to you thanks to unrestricted educational grant from


Back to all articles

Enormous thanks to our visionary sponsors

Myopia Profile’s growth into a world leading platform has been made possible through the support of our visionary sponsors, who share our mission to improve children’s vision care worldwide. Click on their logos to learn about how these companies are innovating and developing resources with us to support you in managing your patients with myopia.