Do optical treatments for the control of myopia progression produce proportional or absolute reductions in progression rates?

Multiple segment spectacle lenses for myopia control. Part 2: Impact on myopia progression

PURPOSE

Initial studies have suggested that multiple segment (MS) spectacle lenses can reduce the progression rate of childhood myopia and axial eye growth. This paper aimed to compare the effectiveness of two different available designs of MS lens and to explore the nature of their control effect.

METHOD

Published data from the only two clinical trials in which changes in mean spherical equivalent refraction (SER) and axial length (AL) for matched groups of myopic children wearing either MS or single-vision (SV) spectacle corrections, recorded over a period of at least 2 years, were further analysed and compared. Both trials involved Chinese children of similar ages and visual characteristics, but the trials were located in different cities. The two MS lenses examined were MiyoSmart or DIMS (Hoya) and Stellest (Essilor).

RESULTS

Absolute changes in SER and AL differed over time during the two trials. However, if the results were expressed in terms of efficacy over successive 6-month periods, then the two MS lenses produced broadly similar results (initial efficacy for the control of myopia progression of about 60%-80%, declining over 2 years to about 35%-55%). Control appears to be absolute rather than proportional.

DISCUSSION

Myopia control may be due to either the additional myopic defocus induced by the MS lenses (i.e., asymmetry of the through-focus image changes about the distance focus) or to the general reduction in image contrast that the lenslets create in the peripheral field.

CONCLUSION

Multiple segment spectacle lenses offer a valuable new approach to the control of myopia progression in children. Further work is required to clarify their mechanism of action and to optimise their design parameters.

One-year myopia control efficacy of cylindrical annular refractive element spectacle lenses

PURPOSE

To evaluate the 1-year myopia control efficacy of a spectacle lens with annular cylindrical microstructures.

METHODS

A total of 118 consecutive eligible children aged 8-12 years with -1.00 D to -4.00 D of spherical component myopia and <1.50 D astigmatism were enrolled between August 2020 and November 2020 at the Eye Hospital of Wenzhou Medical University. Participants were randomly assigned to wear cylindrical annular refractive element (CARE) (n = 61) or single-vision (n = 57) spectacle lenses. Cycloplegic autorefraction (spherical equivalent refraction [SER]) and axial length (AL) were measured at baseline and 6-month intervals. Adaptation and compliance questionnaires were administered during all visits.

RESULTS

Among 118 randomized participants, 96 (81.4%) were included in the analyses (mean [SE] age, 10.4 [0.6] years; 49 [51.0%] were female; mean [SE] spherical equivalent refractive error, -2.67 [0.66] D; mean [SE] axial length, 24.75 [0.77] mm). Adjusted 1-year myopia progression was -0.56 D for CARE and -0.71 D for single-vision spectacle lenses. The difference in progression was 0.14 D (95% CI, -0.04 to 0.32) for CARE vs single vision. Adjusted 1-year eye growth was 0.27 mm for CARE and 0.35 mm for single vision. The difference in eye growth was 0.09 mm (95% CI, -0.15 to -0.02) for CARE vs single vision. All groups adapted to their lenses with no reported adverse events, complaints, or discomfort.

CONCLUSIONS

Among children with myopia, treatment with cylindrical annular refractive element spectacle lenses significantly reduced the rate of axial elongation over 1 year compared with single-vision spectacle lenses.

Flitcroft's model of refractive development in childhood and the possible identification of children at risk of developing significant myopia

PURPOSE

To better understand juvenile myopia in the context of overall refractive development during childhood and to suggest more informative ways of analysing relevant data, particularly in relation to early identification of those children who are likely to become markedly myopic and would therefore benefit from myopia control.

METHODS

Examples of the frequency distributions of childhood mean spherical refractive errors (MSEs) at different ages, taken from previously-published longitudinal and cross-sectional studies, are analysed in terms of Flitcroft's model of a linear combination of two Gaussian distributions with different means and standard deviations. Flitcroft hypothesises that one, relatively-narrow, Gaussian (Mode 1) represents a "regulated" population which maintains normal emmetropisation and the other, broader, Gaussian (Mode 2) a "dysregulated" population.

RESULTS

Analysis confirms that Flitcroft's model successfully describes the major features of the frequency distribution of MSEs in randomly-selected populations of children of the same age. The narrow "regulated" Gaussian typically changes only slightly between the ages of about 6 and 15, whereas the mean of the broader "dysregulated" Gaussian changes with age more rapidly in the myopic direction and its standard deviation increases. These effects vary with the ethnicity, environment and other characteristics of the population involved. At all ages there is considerable overlap between the two Gaussians. This limits the utility of simple refractive cut-off values to identify those children likely to show marked myopic progression.

CONCLUSIONS

Analysing the frequency distributions for individual MSEs in terms of bi-Gaussian models can provide useful insights into childhood refractive change. A wider exploration of the methodology and its extension to include individual progression rates is warranted, using a range of populations of children exposed to different ethnic, environmental and other factors.