Can we predict success with orthokeratology?

Title: Categorisation of myopia progression by change in refractive error and axial elongation and their impact on benefit of myopia control using orthokeratology

Authors: Pauline Cho (1), Sin Wan Cheung (1), Maureen V Boost (1)

1: School of Optometry, The Hong Kong Polytechnic University, Kowloon, Hong Kong SAR, China.

Date: Dec 2020

Reference: Cho P, Cheung SW, Boost MV. Categorisation of myopia progression by change in refractive error and axial elongation and their impact on benefit of myopia control using orthokeratology. PLoS One. 2020 Dec 29;15(12):e0243416. [Link to open access paper]

This self-controlled case series by Pauline Cho and colleagues was sponsored by a Collaborative Research Agreement between PolyU and Menicon, and aimed to identify suitable candidates for myopia control with orthokeratology. It was conducted at the Hong Kong Polytechnic University and investigated the effectiveness of pre-treatment axial elongation (AE) and changes in refractive sphere (RE) in predicting the success in orthokeratology.

Method: 

66 myopic children aged 8-16 years were included, with measurements taken before and after 7 months of wearing single vision spectacles. Subjects were grouped according to age (6 to 9 years, 9 to 13 years and 13 to 16 years) and myopia progression was classified as slow (AE <10mm, RE change <0.29D), moderate (AE >10mm but <0.20mm; RE change 0.29 to <0.58D) or rapid (AE >0.20mm; RE change >0.58D). Outcomes of orthokeratology treatment were evaluated with respect to age group and reduction in axial elongation after treatment. Orthokeratology effect was determined as either:

1. Ineffectual: no change or an increase in axial elongation
2. Not clinically significant: axial elongation ≤  0.05mm
3. Significant benefit: reduction in axial elongation >0.05mm

Results: 

• Those who were categorised as "slow progressors" by axial elongation and, of whom 95% were similarly categorised by M change, none benefited from orthokeratology
• Those who were categorised as "moderate progressors" by axial elongation, 77% and 23% displayed slow and moderate change, respectively, the majority (73%) benefitted from orthok lens wear 
• The vast majority of "rapid progressors" showed significant benefit after orthokeratology. 
• After orthokeratology lens wear, "rapid progressors" had the greatest reduction in axial elongation. In contrast, "slow progressors" had virtually no change in axial elongation.

• Clinically, this means that fast progression of axial elongation is a good indicator of subsequent success of orthokeratology treatment.
• On the other hand, delaying commencement of therapy may be prudent for children with slow progression as results indicate that they would be unlikely to benefit from intervention. 
• Lastly, the use of refractive error to determine progression rate was unreliable in this study, with change in refractive error frequently underestimating rapid progression of axial length. Consequently, it is ideal to use axial elongation to determine progression if this is available to you in clinical practice.

This study utilised orthokeratology as the means of myopia control. Clinically, orthokeratology may not be appropriate for all patients and thus similar studies should be undertaken that consider other methods of myopia control, including soft contact lenses and atropine.

Title: Categorisation of myopia progression by change in refractive error and axial elongation and their impact on benefit of myopia control using orthokeratology

Authors: Pauline Cho, Sin Wan Cheung, Maureen V Boost

Purpose: To compare the value of pre-treatment axial elongation (AE) and changes in refractive sphere (M change) for predicting the success in orthokeratology (ortho-k), in order to better identify suitable candidates for myopia control.

Methods: This study further analysed the data of 66 subjects receiving 7-month ortho-k treatment, following a 7-month observation period, during which single-vision spectacles were worn. Rate of myopia progression was determined by AE and M change and subjects categorised as slow, moderate, or rapid progressors based on these changes. Outcomes of myopia control, based on the AE reduction after ortho-k, were classified as 'ineffectual', 'clinically insignificant', or 'beneficial'.

Results: Of the 20 subjects, initially categorised as slow by AE and, of whom 95% were similarly categorised by M change, none benefitted from ortho-k. In contrast, of the 22 subjects with moderate AE, 77% and 23% displaying slow and moderate M change, respectively, the majority (73%) benefitted from ortho-k lens wear. The 24 subjects with rapid AE were poorly identified by M change, with only 21% correctly categorised. The vast majority of rapid progressors showed significant benefit after ortho-k.

Conclusion: Progression of AE is a good indicator of subsequent success of ortho-k treatment. Delaying commencement of therapy is prudent for children with slow progression as results indicate that they would be unlikely to benefit from this intervention. As change in refractive error frequently underestimates rapid progression of AE, its value for identifying appropriate candidates for myopia control is poor.

Link to open access article is here