What is the risk-to-benefit balance for myopia control contact lenses in children?

Paper title: Childhood and lifetime risk comparison of myopia control with contact lenses

Author: Kate L. Gifford

School of Optometry and Vision Science, Institute of Health and Biomedical Innovation, Faculty of Health, Queensland University of Technology, 60 Musk Avenue, Kelvin Grove, QLD, 4059 Australia

Date: Feb 2020

Reference:  Gifford KL. Childhood and lifetime risk comparison of myopia control with contact lenses. Cont Lens Anterior Eye. 2020 Feb;43(1):26-32. [Link to abstract]

Eye care practitioners can be reluctant to fit children with contact lenses, presumably due to hygiene and infection concerns with young patients.

Efron et al investigated practitioners fitting habits in 2019.¹ They found only 2.3% of new fittings were for myopia control in children. Contact lenses wear offers many advantages to children over spectacles. With an increased uptake of myopia management, the number of new fittings to children may now be higher.

However, the lifelong ocular benefits of myopia reduction from contact lens interventions need to be understood against the risk of serious infections such as microbial keratitis (MK).

This analysis paper utilized peer-reviewed data to calculate the absolute risks of MK incidence over childhood and lifelong contact lens wear periods and compared this to the relative risk of visual impairment from increasing axial length and myopic refractive error.

Using PubMed as a source, the author conducted a search for studies which contained data on the absolute incidence of MK for daily disposable, soft reusable (including when used for extended wear) and orthokeratology (OK) lens types in both adult and child wearers.

A model was formulated in order to present the risk of one MK episode over a period of childhood contact lens wear (from age 8 to 18yrs), lifelong contact lens wear (age 8 to 65yrs) for daily disposable soft, reusable soft (including wear on an extended wear basis) and OK. The likelihood of MK over a lifetime (up to the age of 75yrs) for a non-contact lens wearer was also calculated to serve as a comparison. The MK risk was taken to be of any episode and not only cases causing vision loss. The cumulative risk of vision loss before the age of 75 due to high myopia and axial length growth was extracted from the work of Tideman et al.²

The classification system for the frequency of adverse events from the Council of International Organisations of Medical Sciences (CIOMS) was used to present the findings.  This classifies adverse events as either 'very common' (more than 1 in 10), 'common/frequent' (between 1 in 100 and 1 in 10), 'uncommon/infrequent' (between 1 in 1000 and 1 in 100), 'rare' (between 1 in 10000 and 1,000) and 'very rare' (less than 1 in 1,0000).

The risk comparisons found that:

• For individuals with axial lengths of 26mm or more and myopia of 6D or more, the risk of impairment from high myopia over their lifetime is 'very common' with more than 1 in 10 risk.
  • This is greater than the lifetime risk of developing MK in any contact lens modality, where the risk from daily disposables and reusable soft contact lenses is 'uncommon/infrequent' (1 in 431 and 1 in 116, respectively) and from OK lenses where the risk is 'common' (1 in 67).
  • Adults wearing soft contact lenses on an extended wear basis had a 'very common' risk of 1 in 7.7 over the same period.
• For individuals with axial lengths below 26mm and myopia lower than 3D, the risk of vision impairment from myopia over their lifetime is 'very common to common' with a risk between 1 in 10 and 1 in 100.
  • In comparison, a lifetime of daily disposable wear gives the same risk of MK infection (1 in 76.2)
  • However, reusable soft or OK lenses worn over the same period present higher risks of 1 in 15 and 1 in 21, respectively.
• For children wearing contact lenses for 10 years (ages 8-18), the likelihood of MK was found to be:
  • The lowest risk was for children fit with daily disposable soft contact lenses, where MK was 'uncommon/infrequent' with a likelihood of 1 in 431.
  • Reusable soft contact lenses gave an 'uncommon/infrequent' risk of less than 1 in 100.
  • OK lenses showed the highest risk for MK with a 'common/frequent' risk of 1 in 67.
• Over a lifetime of full-time contact lens wear, the likelihood of MK infection was found to be:
  • 'Common'/frequent risk' with reusable soft lenses and OK lenses with 1 in 15 and 1 in 21.5 risks, respectively.
  • Daily disposable wear gave a 1 in 76.2 risk of MK infection
  • The highest chance of MK infection was 'very common' at 1 in 7.7 with extended wear
  • By comparison, no lens wear over a full 75-year period had a 1 in 95.2 risk of MK.

The scenario of considering fitting children with contact lenses is a realistic situation for clinical practice where daily disposable myopia management options are available.

• Where myopia is less, so is the risk of future impairment (1 in 26). However, compared to the risk of MK from wearing daily disposables over the same time period, low myopes are still at more risk of impairment from myopia than developing MK.

We can treat the childhood period from 8 to 18yrs as a relatively 'short-term' stage where the goal is to maximise myopia control while balancing the infection risks.

A risk for MK for childhood contact lens wear was included in this review due to historical misgivings from both parents and practitioners when considering fitting children.

• For myopic children, the benefits they will receive from managing their myopia statistically outweigh the risks of serious infection from wearing the lenses.
• The risk of MK with contact lens wear of any time from 8 to 18yrs old is lower than that of a lifetime risk of visual impairment from myopia stronger than 6D and axial lengths longer than 26mm (1 in 33), particularly if daily disposable lenses are worn.
• Bullimore³ found that the risk of corneal infiltrative events in teenagers was no more likely than in adults and that the risk could be much lower in pre-teens.
• Some of the most commonly accepted risk factors for MK in adults are purchasing lenses online and being smokers, both of which are not concerns in children and reduce the risk for MK for them significantly.

Eye care practitioners can be confident that they are fitting children with myopia controlling contact lenses - especially daily disposable - with the child's best interest in mind. The myopia and the lifetime risk of vision loss will be reduced while also providing a high safety profile.

Future research could further our understanding of contact lens complications arising from fitting children, as some of the MK risks used in calculations were from adult data, as childhood data of the same level was not available.

• As the MK rates for adults has been found to be higher than that for children, this may make these calculations skewed towards a higher infection rate for the children's groups than is realistic.
• Further research could confirm the long-term safety of children wearing contact lenses where the amount of myopia management fittings could be expected to rise in the coming years. Since this publication, one study reporting six-years of daily disposable contact lens wear in children in a clinical trial reported no cases of MK.

Title: Childhood and lifetime risk comparison of myopia control with contact lenses

Authors: Kate L. Gifford

Purpose: The relative risks of ocular pathology with increasing myopia have been described; the absolute lifetime risk of vision impairment from myopia is yet to be compared to the childhood and lifetime risks of contact lens wear for myopia control

Methods: Using peer-reviewed data, the absolute risks of microbial keratitis (MK) in daily disposable soft, reusable soft and orthokeratology contact lens (CL) wear were calculated over both a childhood (age 8-18) and a lifetime (age 8-65) of CL wear. This was compared to the previously published cumulative risk of vision impairment by age 75 based on increasing myopia and axial length. Data were converted utilizing the Council of International Organizations of Medical Sciences (CIOMS) classification system for frequency of adverse events, with 95 % confidence intervals included.

Results: The lifetime risk of vision impairment in axial lengths over 26mm and more than 6D of myopia is greater than the lifetime risk of MK in any CL modality, except for adult SCL extended wear. If axial length is below 26mm and myopia lower than 3D, a lifetime of CL wear is more risky in comparison, except in the case of daily disposable wear. Ten years of childhood CL wear of any modality presents lower likelihood of MK than any comparable risk of vision impairment

Conclusions: The comparative lifetime risks of contact lens wear commenced at age 8 for myopia control are less than the lifetime risks of vision impairment with myopia more than 6D or axial length more than 26 mm. When only childhood CL wear is considered, the risk comparison is clearly skewed towards the positive impact of CL wear, especially in daily disposable wear. Clinicians should be confident to proactively recommend myopia control CL wear to younger children, as both the safety profile and potential preventative ocular health benefits are evident

[Link to abstract]