Which is more effective: DIMS or Ortho-k?

This study followed 540 children in China aged 7 to 14, divided into three groups of 180 each: those using DIMS lenses, ortho-k, and single-vision spectacles (SVS), and 496 children completed the 12-month study. Ortho-k lenses were from Euclid, Inc. with a back optic zone diameter (BOZD) of 6.2mm. After a one-year follow-up, changes in axial length (AL) were analyzed among the groups. The subjects were further categorized into subgroups based on the degree of myopia: low (-0.50D to -1.50D, n=171), moderate (-1.50 to -3.00, n=159), and high (-3.00D to -5.00D, n=166). Statistical methods used were one-way ANOVA and multiple linear regression to compare AL elongation and assess influencing factors.

The amount of axial length change was as follows:

The statistical outcomes were as follows for the refractive classification subgroups.

• Low myopia subgroup: AL changes were significantly different among the groups. OK (n= 58) and DIMS (n=58) lenses showed no significant difference between them but were both more effective in reducing AL elongation compared to SVS (n=55). The groups weren’t matched for axial length at baseline, with the DIMS group having the longest axial lengths.
• Moderate myopia subgroup: Ortho-k (n=55) showed the least AL elongation compared to DIMS (n=51) lenses and SVS (n=53). The groups were matched for axial length at baseline.
• High myopia subgroup: Ortho-k (n=58) had the least AL elongation. No significant differences were observed between the DIMS (n=56) and SVS (n=52) groups. All three groups were matched for axial length at baseline. 

In the ortho-k group overall, there was the least axial elongation in the ‘high’ myopia group, which the authors cite is a different finding to two previous studies. This does not indicate ortho-k was less effective for lower myopia, since its efficacy was similar to DIMS - more so that the high myopia group had a much smaller axial elongation. The ages of the low, moderate and high myopia ortho-k groups appeared similar - the authors cite this result could be related to the defocus levels provided by ortho-k treating for high myopia. It’s important to note that ‘high myopia’ was defined here as more than 3.00D, whereas the IMI Definition is at least 6.00D.²

In the DIMS group, the axial elongation was similar across the refractive classification groups. This indicates that DIMS was similarly effective for myopia control in children with baseline myopia from -0.50 to -5.00D.

The authors noted that the SVS group was older in the high myopia group, hence the slower eye growth and statistical similarity to DIMS cited. 

Across all participants, younger age and lower initial baseline axial length were both correlated with faster axial growth in 12 months. This can be seen in the table above, where since higher myopia correlates with longer baseline AL, the high myopia group’s axial elongation numbers all appear lower than those for low and moderate myopia. 

Records from 167 myopic (-0.75D to -4.00D) children from Peking University were examined to compare the efficacy of DIMS spectacle lenses, ortho-k, DIMS combined with 0.01% atropine (DIMSA), and ortho-k combined with 0.01% atropine (OKA). Ortho-k lenses were again from Euclid, Inc. but with a BOZD of 6.6mm. Axial length (AL) was measured at baseline and every 3 months over a 12-month period.

The axial length change results were as follows:

 The results indicate:

• Similar efficacy between ortho-K and DIMS: After 12 months, the AL changes were similar for the ortho-k group and the DIMS group, with no significant difference, indicating comparable efficacy in controlling myopia progression. 
• Overall Results: After 12 months, the OKA group and the DIMSA group showed significantly slower axial elongation compared to the Ortho-k and DIMS groups alone, indicating that the addition of atropine was effective in enhancing myopia control. The difference between groups was 0.08mm additional efficacy for OKA and 0.07mm for DIMSA.
• Subgroup aged 6 to less than 10 years (n=98): Ortho-k + atropine (OKA) appears more effective than DIMS lenses in this age group (n=26 for OKA and n=24 for DIMS). All other treatment sub-groups were similar. 
• Subgroup aged 10 to 14 years (n=69): Most treatment groups were similar, with only DIMS + atropine (n=18) being more effective than OK (n=17) in this group. Other differences reported are likely statistically insignificant due to small numbers and multiple comparisons.  

Although results were not stratified by refractive error, it was concluded that similar efficacy was noted between ortho-k and DIMS lenses in low myopes, since the majority of this dataset fell into this refractive category. Despite the limitations of small treatment sub-groups, particularly when stratified by age, this study does indicate a boost to myopia control efficacy for both ortho-k and DIMS through addition of 0.01% atropine, over 12 months.

The two studies are different, with the first being larger and prospective, and the second being smaller and retrospective. Prospective studies are typically favoured over retrospective studies when it comes to evidence quality, as they are more capable of managing biases and determining temporal relationships.³ The much higher participant numbers in the first study can lend to more robust statistical relationships compared to studies with smaller numbers. Nonetheless, retrospective studies can still offer valuable insights.

Comparison between the two studies is also complicated by the different ortho-k lens parameters. The first study uses an ortho-k lens with BOZD of 6.2mm whereas the other is 6.6mm. Studies suggest that a smaller BOZD provides a greater short-term myopia control effect,^4-5 which may explain why ortho-k was found to be potentially more effective than DIMS for moderate-to-high myopia in the first study. More on this topic can be found in our article Customizing ortho-k: what does it mean and is it needed?

Despite these differences, the studies are similar in drawing from a population of Chinese children with comparable ages, and agree that ortho-k and DIMS lenses are effective in slowing axial elongation with similar efficacy in low myopes. In study 1, as myopia severity increases, ortho-k appeared to become more effective compared to DIMS. This could be in part due to differences between the refractive groups when stratified by treatment. In study 2, ortho-k and DIMS had similar efficacy, with the addition of atropine showing benefit overall, with some differences by age sub-groups. Given the small numbers in these treatment sub-groups by age, conclusions about the best treatment by age cannot be drawn - instead there is the overall picture of similar efficacy of ortho-k and DIMS, and the boost provided by 0.01% atropine. 

There were limitations in both studies, in terms of their measures being limited to 12 months, dividing participants into numerous smaller groups for analysis, and lack of randomization, which provides the gold standard in evaluating myopia control efficacy.^6,7 While these studies together provide indication of the similar efficacy of DIMS and ortho-k for myopia control, the first study points to ortho-k being superior for moderate-to-high myopia, and the smaller second study shows a boost to both through combination with atropine 0.01%. There was not enough data to determine whether younger or older age groups benefit the most from combination treatment. A longer-term randomized controlled trial would help delineate these differences, but the insightful data provided by both studies indicate both DIMS and ortho-k are similarly valuable tools for slowing myopia progression in children.