Astigmatism and maternal myopia as important factors affecting success rate of DIMS lens treatment

Introduction

Myopia has witnessed a rapid increase in prevalence in recent years becoming a global public health concern. Over 30% of Europeans are affected by myopia,1 with numbers surpassing 40% among school-age children2 contributing to a significant vision concern within the region. Current estimated prevalence is slightly higher in Western Europe (36.7%), compared with Eastern Europe (32.2%).3 Nevertheless, based on the representative nationwide screening programme conducted on adults in the past 10 years, myopia prevalence is 43.45% in Hungary, and it is three times more frequent in younger people (58.7%; 18–35 years) compared with older age groups (19.4%; 56–70 years).4 This is in stark contrast with data from the first half of the 20th century, when myopia prevalence was well under 10% among schoolchildren in Budapest.4 Globally, myopia’s prevalence is surging, with projections suggesting that by 2050, nearly half of the world’s population could be impacted by this refractive error, with estimates of 65%, 56%, 54% and 50% in Asia, Western, Central and Eastern Europe, respectively, if serious countermeasures are not taken.3 Myopia’s development is influenced by a complex interplay of genetic and environmental factors. Prolonged near work, limited outdoor time, education level, family history of myopia and certain ethnic backgrounds are key risk factors associated with its onset and progression.5 6 High myopia, characterised by a spherical equivalent of –6.0 D or worse, carries substantial ocular risks. These include myopic maculopathy, retinal detachment and glaucoma, leading to severe visual impairment and potential blindness.7 8

Researchers and practitioners have been exploring innovative ways to control myopia progression. Several widely tried therapeutic approaches, including undercorrection,9–13 pinhole glasses, blue light blocking glasses, bifocal glasses,14 15 progressive addition spectacle lenses,16–21 daytime single-vision soft contact lenses/rigid gas permeable contact lenses22–27 and others, have demonstrated limited effectiveness in significantly retarding the progression of myopia. Research suggests that these interventions often fail to address the underlying mechanisms driving myopia’s development and may provide only minimal benefits in controlling its advancement. Promisingly, effective myopia control strategies encompass a range of interventions, including increased outdoor time,28–34 reduced engagement with smartphones and near tasks,35–38 as well as the utilisation of advanced technologies like DIMS (defocus incorporated multiple segments) lenses,39–44 highly aspheric lenslet lenses,45–47 soft multifocal contact lenses,44 48–54 orthokeratology55–59 and low-dose atropine eye drops.60–67 These approaches have demonstrated the potential to counter myopia progression by addressing various contributing factors and are paving the way for a more proactive approach to visual health management.68

One such ground-breaking approach is the use of spectacle lenses with DIMS technology; DIMS technology operates by integrating a central optical zone for correcting distance vision and an annulus of tiny circular segments with a relative positive power of 3.50 D distributed across the mid-peripheral area, each ~1 mm in diameter, in a honeycomb pattern.39 44 69 70 This arrangement induces peripheral myopic defocus while maintaining clear vision, harnessing the principles of peripheral defocus and simultaneous vision to curtail axial elongation and mitigate myopia progression. Notably, these lenses offer a minimally invasive solution, making them a promising avenue for managing myopia while prioritising patients’ well-being.43 71

Although most of the available data concern Asian populations, a recent study has reported a significant efficacy rate of approximately 50–60% in reducing myopia progression among European populations using DIMS lenses.72 Moreover, Truckenbrod et al73 presented data indicating a parallel pattern of axial length (AL) growth between the Asian and European populations, and research on the adaptation and acceptance of DIMS among Chinese children contributed valuable insights, that apart from slightly affected mid-peripheral vision, DIMS lenses received good tolerance and acceptance by Chinese children.43

Even though there is a growing body of evidence of the effectiveness of DIMS lenses, the existing studies, except one,74 have limited inclusion to moderate myopia with also a limit on the maximum allowed astigmatism. Our study, therefore, was aimed to assess the effectiveness of DIMS lenses in attenuating myopia progression within a European paediatric cohort, encompassing a diverse dioptre range from −0.88 spherical equivalent refraction (SER) to −8.25 SER with special focus on investigating the impact of baseline optic parameters as well as parental myopia on the efficacy of DIMS lenses. Additionally, we endeavoured to demonstrate the broad age range tolerance of DIMS lenses, spanning from 4 to 17 years. Our results highlight the significance of tailored strategies for children with familial predisposition and astigmatism as risk factors for therapeutic failure and underline adaptability of DIMS therapy across diverse paediatric age groups and a wide range of dioptres.

Materials and methods

Results

Changes in spherical equivalent

Baseline characteristics of the study population can be found in table 1. The mean (±SE) unadjusted myopia progression (SER) over the 1-year period for the whole study group (N=62) was −0.40±0.05 D, with 31 (50%) patients showing no progression at the end of the 1-year period (figure 1A). To investigate the possible contribution of clinical factors to the individual variation in myopia progression, an analysis of covariance approach was adopted, where both CFB_6m and CFB_12m were included as dependent variables. We examined age, baseline and familial optical parameters, namely baseline SER, the presence or lack of clinically significant astigmatism (ie, type of myopia) at baseline, and parental myopia (maternal and paternal myopic dioptre) and their interaction with time to determine their effect on therapy outcome, that is, the SER change from baseline. As expected, time had the most pronounced effect on progression (F_(1,56)=24.92, p<0.0001), as patients showing progression despite DIMS treatment progressed even further from the 6-month to 12-month visit. Patients’ age did not have a significant main effect on progression (F_(1,56)=3.24, p=0.077) but significantly interacted with time (F_(1,56)=12.44, p=0.0008). Thus, patients of different ages had different patterns in their progression dynamics. Pearson correlations revealed that while there was no age-specific progression at 6 months (CFB_6m vs age: r₍₆₀₎=0.18, p=0.17), correlations between further progression and age (CFB_12m−CFB_6m vs age: r₍₆₀₎=0.42 p=0.001), and 12-month progression and age (CFB_12m vs age: r₍₆₀₎=0.37, p=0.003) were significant. This was due to the fact that while older (≥10 years) patients’ progression slowed down after 6 months, younger patients progressed further at a similar rate achieving significantly larger progression at 12 months (figure 1B, age group×time: F_(1,56)=14.53, p=0.0003, post-hoc p=0.0004 for CFB_{12m_YOUNG} vs CFB_{12m_OLDER}). There was also no effect of baseline SER D (main effect: F_(1,56)=0.001, p=0.97; interaction with time F_(1,56)=0.04, p=0.85), indicating a similar efficacy profile of DIMS lenses for high as for moderate myopia.

Figure 1

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Model-adjusted mean progression in SER from baseline to 12 months. (A) Group progression (N=62). (B) Different progression dynamics of patients <10 years and ≥10 years old. Younger patients show faster progression, which does not taper off after 6 months. (C) Different progression rates between patients with astigmatism and those with axial myopia, the former showing significantly greater progression. (D) 12-month change as a function of maternal myopia. Only patients with mothers with severe (≥9 D) myopia show markedly larger progression. The values are least-squares estimates with continuous predictors as age, baseline dioptre, maternal and paternal dioptres fixed at their mean. Error bars indicate ±SE. SER, spherical equivalent refraction.

Importantly, progression was also significantly affected by the presence of astigmatism (F_(1,56)=5.20, p=0.026) with the astigmatic group displaying significantly greater overall progression compared with the purely axial myopic group (figure 1C, −0.49±0.07 SER vs −0.26±0.07 SER for patients with astigmatic and purely axial-type myopia at 12 months, respectively). This pattern was present throughout the study (time×astigmatism F_(1,56)=1.54, p=0.22). When assessing the presence of astigmatism in the non-progressing group of patients, there was a significant relationship between the presence of astigmatism and progression in SER (χ²=9.79, p=0.0018; 81% vs 41% of patients were astigmatic in the progressing vs non-progressing groups, respectively). The same pattern was found when analysing CFB_12m refractive data transformed into Long’s matrix of (f11 f12 f22)78–80 using an analogous model (online supplemental table 1; main effect of astigmatism: F_(1,54)=4.45, p=0.039; mean change –0.37/–0.22×79 vs −0.23/−0.04×142 for patients with and without astigmatism, respectively). Interestingly, the change in the f12 component, which is computed from the DCYL and its respective axis, showed virtually no difference between these patient groups (online supplemental figure 1). Therefore, it seems that the significant difference in SER change in patients with astigmatic and axial-type myopia comes from the different degree of change in spherical power, which could reflect the different rates of axial elongation between these groups.

Lastly, parental myopia also had a notable contribution to progression: maternal (F_(1,56)=3.90, p=0.053), but not paternal myopic dioptre (F_(1,55)=0.14, p=0.71), had a strong tendency to affect progression, with no significant interaction with time (all F≤1.01, p≥0.32). This pattern was driven by patients having a mother with severe myopia showing the most progression (figure 1D). The distinguished role of the mother—at least in our sample—is also supported by the finding that our pool of mothers displayed significantly higher myopia compared with that of the fathers (two-sample Kolmogorov-Smirnov test: D_(62,62)=−0.30, p<0.01; −2.90±0.41 D vs −1.09±0.24 D for mothers and fathers, respectively).

Changes in AL

The mean unadjusted 12-month increase in AL in a subset of our study group (N=33), where AL was measured, was 0.16±0.03 mm (figure 2A). The extent of axial elongation was significantly dependent on patients’ age (F_(1,27)=10.42, p=0.003), with younger patients showing more pronounced elongation, while the effect of parental myopia only showed a non-significant trend (F_(1,27)=3.32, p=0.079 and F_(1,27)=2.77, p=0.11 for maternal and paternal myopic dioptres, respectively). Baseline AL had no effect (F_(1,27)=0.021, p=0.65). Notably, the presence of astigmatism had a significant effect on axial elongation as well (F_(1,27)=4.73, p=0.039; 0.20±0.05 mm vs 0.12±0.04 mm for patients with and without astigmatism, respectively). Importantly, the analysis of a larger cohort of German children wearing single-vision spectacles yielded contrasting results. While the axial elongation was also dependent on patients’ age (F_(1,182)=46.94, p<0.0001), with younger patients progressing at a larger rate, the presence of astigmatism had absolutely no effect on myopia progression (F_(1,182)=0.003, p=0.96; 0.12±0.02 mm vs 0.11±0.01 mm for patients with and without astigmatism, respectively). In addition, maternal myopia had also no effect on progression (F_(1,182)=0.54, p=0.46), as opposed to baseline AL, which influenced AL elongation (F_(1,182)=9.17, p=0.003). These results obtained with single-vision children corroborate our findings that the efficacy of DIMS lenses in slowing down the myopia progression of patients with astigmatism seems to be less, compared with patients with axial-type myopia.

Figure 2

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Group average and model-adjusted mean progression in axial length at 12 months split by age group and presence of astigmatism. (A) Data for children wearing DIMS lenses. The values are least-squares estimates with continuous predictors as age, baseline dioptre, maternal and paternal dioptres fixed at their mean (N=33). (B) Data for children wearing single-vision spectacles (N=187). Error bars indicate ±SE. *P<0.05, **p<0.01. DIMS, defocus incorporated multiple segments.

QoL questionnaire

The results of the QoL questionnaire demonstrated an excellent long-term overall acceptance of the DIMS spectacles for both the entire group (figure 3A) and for the youngest patients aged 4–7 years (figure 3B). In addition, there was very low incidence of side effects (figure 3C), which were almost completely resolved after 12 months except for a few cases of occasional eye strain, which seemed to persist throughout the study. Importantly, the young age group showed a very similar pattern (figure 3D) demonstrating the usability of DIMS glasses even at a young age. Interestingly, DIMS spectacles scored somewhat higher in user satisfaction and lower in the incidence of side effects compared with patients’ previous single-vision glasses, which also emphasises its clinical relevance.

Figure 3

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Results of the quality of life questionnaire. (A) Incidence of reported symptoms in the whole group (B) and in patients under 8 years old (N=8). (C) Patient satisfaction in the whole group (D) and in patients under 8 years old. Scales for rating ranged from 1 to 5 (never to always and poor to excellent, respectively). Error bars indicate ±SE.

Discussion

Our objective was to investigate the effectiveness of DIMS technology lenses within a more diverse paediatric population, building upon the established and promising literature. This endeavour aimed to deepen our understanding of the variables that might impact the success of this therapeutic approach. We have found that the presence of astigmatism in our group of patients with myopia resulted in larger progression compared with patients with purely axial myopia, potentially diminishing the effects of DIMS lenses in slowing myopia progression. In addition, patients with severe maternal myopia also experienced a significantly more pronounced progression. Finally, younger age was associated with faster progression, which, unlike that of older children, did not slow down after 6 months, achieving larger progression at 12 months. These findings underline the importance of astigmatism, severe maternal myopia and young age as risk factors for myopia progression, even when using DIMS spectacles.

When comparing the mean progression of our patients with other published results, we found our results to be largely consistent with the 1-year results of Nucci et al72 in a European population but higher than the –0.17 D SER progression found by Lam et al69 in an Asian population. While the impact of ethnic differences on myopia progression is somewhat controversial,73 81 the difference may be attributed to the fact that both the current and the Nucci et al study predominantly included evolutive myopes who have shown myopia progression in the previous year, and larger astigmatism was allowed. Nevertheless, among our patients, 31 (50%) did not progress by the end of the 1-year period, defined by no dioptric deterioration exceeding −0.5 D SER in any eye.77 Taken together, the mean progression and per cent of non-progressing myopes also show close resemblance to the only available large-scale retrospective study conducted in real-world clinical settings.74 It has been shown that both children and adults tolerate DIMS lenses well,43 69 82 with minimal mid-peripheral visual acuity and contrast sensitivity reduction in nasal and temporal gaze. We assessed acceptance throughout the 1-year treatment and obtained similar results, with minimal habituation complaints in children wearing DIMS lenses, primarily in the initial period of wear. Young children exhibited a similar profile highlighting the clinical relevance of DIMS spectacles. Interestingly, DIMS lenses scored somewhat higher in user satisfaction and lower in the incidence of side effects compared with patients’ previous single-vision glasses, indicating comparable usability with the standard of care.

Previous larger DIMS studies69 70 72 tended to include participants with mild and moderate myopia not exceeding –5.0 D (SER). Consequently, there are limited data on the efficacy of DIMS lenses on patients with high myopia. Verkicharla et al83 found that 1-year myopia progression was dependent on initial dioptres in children with myopia wearing single-vision lenses, with the largest progression seen in severe myopes (>9 D SER), followed by high, moderate and mild myopes, which is in line with findings of other studies.84 85 However, studies evaluating the efficacy of DIMS lenses did not find a similar relationship between initial dioptres and progression rate, as including baseline SER as a covariate did not affect therapy outcomes.69 72 Our results also support the idea that the initial dioptre value is not related to the degree of progression when using DIMS spectacles for myopia control, in line with the above findings. Therefore, patients with high myopia can also benefit from this therapy.

It is well-known that curvatural myopes with a small AL form a well-defined group of patients with a low risk of progression,77 and the effect of astigmatic defocus on the progression of myopia is an area of intense research.86–89 Nevertheless, in myopes showing progression, the presence of astigmatism is somewhat overlooked, as the commonly used practice of calculating the spherical equivalent merges the contribution of spherical and cylinder dioptres. Our results suggest that the efficacy of DIMS lenses is higher in pure axial myopes without astigmatism (≤−0.5 DCYL), as mean progression (SER) was significantly lower in axial myopes, and there was a significant relationship between astigmatism and myopia progression: progressing myopes were twice more likely to have had astigmatism compared with non-progressing myopes. This group difference was reflected in spherical dioptre (f11 and f22 Long’s matrix components of refractive power) and AL alterations, while no difference in the change in f12 component, reflecting only DCYL was observed between the two groups. Importantly, there was no difference in AL elongation between children with axial and astigmatic myopia wearing single-vision spectacles. Indeed, the presence of astigmatism was also related to the lack of improvement in children with amblyopia as a result of augmented reality dichoptic training.90 Moreover, imposing both spherical and cylindrical hyperopic defocus early in life was found to lead to differential changes in eye anatomy compared with purely spherical hyperopic defocus in chicks.86 Myopic astigmatic defocus also had a significantly different impact on changes in choroidal thickness after short-term exposure compared with spherical myopic defocus in humans.89 Our findings suggest that astigmatism is not an overall risk factor for progression. However, it may disrupt the uniformity of peripheral myopic defocus, potentially challenging the effectiveness of DIMS technology. Another possibility is that axial elongation and changes in corneal curvature are influenced by separate, interdependent biological processes87 88 and DIMS technology may primarily influence the former. Both hypotheses warrant further investigation in dedicated patient groups.

Our findings also indicate that age significantly influences myopia progression, with younger patients exhibiting greater progression. This is in line with results obtained with DIMS lens use and the normal progression of myopia.69 81 83–85 Additionally, we demonstrated that the rate of progression is similar in the first 6 and second 6 months in younger patients, in contrast to children aged 10 years and older, where it slows down after the first 6 months. Moreover, in our patient group, maternal myopia also emerged as an important factor for progression, especially in the case of severe maternal myopia. Interestingly, our pool of mothers demonstrated much higher incidence and severity of myopia compared with the fathers. It is possible that children with mothers with severe myopia having high dioptres are indeed more susceptible to myopia, but it is also plausible that mothers with myopia, being more aware and concerned,91 may seek out new therapeutic options sooner. The significance of parental myopia is equivocal in the literature as it emerges as a predisposing factor in some studies,28 92–94 whereas others do not find that it significantly affects progression69 81 and was also shown to affect progression using single-vision and progressive-addition lenses differently.95 Thus, this question merits further scrutiny.

Our study has some limitations, however. The limited availability of relevant literature on the effect of astigmatism on myopia progression makes it challenging to interpret the impact of astigmatism on DIMS therapy. One potential approach to address this issue is to reanalyse existing datasets on myopia progression using DIMS spectacles while considering astigmatism to evaluate its effect on progression. Another possible direction would be to explore newer lens designs in this context in a prospective study, comparing them with DIMS technology within a dedicated group of patients specifically selected for this purpose with careful consideration of astigmatism, age and parental myopia. In addition, keratometric measurements alongside standard measurements would be valuable to better characterise the change in astigmatism.

Taken together, our results underline the importance of paying special attention to young children with myopic astigmatism, especially those with a family history of severe maternal myopia as our results suggest that in the European population, astigmatism, young age and severe maternal myopia are risk factors for suboptimal outcomes following DIMS therapy. Further research is necessary to elucidate the impact of astigmatism on myopic defocus therapy.