November 1, 2023
By Dwight Akerman, OD, MBA, FAAO, FBCLA, FIACLE
To determine the success of any juvenile-onset myopia intervention, it is vital to consider the target for myopia progression management. Is the treatment goal to stop axial length growth or simply slow progression? How should axial length growth in children undergoing myopia management treatment be compared to average eye growth in emmetropic children of the same age? What treatment effect is required to be considered clinically meaningful?
Eye growth is highest in the first years of life. According to Gordon and Donzis, 1985, at birth, the average axial length is about 16.8 mm, which increases to 22.3 mm at 6 years of age, 23.1 mm at 9 years of age, and 23.6 mm in the emmetropic adult population. Most eye growth occurs in the very first months to the first years of life. After this period, the corneal curvature is relatively stable, while flattening the crystalline lens balances axial elongation. When this complicated balancing process is disturbed, mismatches between the ocular components will result in ametropia. If the axial length grows too quickly, the compensation by flattening the crystalline lens is lost, and the child develops myopia.
According to Tideman et al., 2017, the mean axial length growth between 6- and 9-year-old (male and female) European children is:
- Myopia: 0.34 mm/year
- Emmetropia: 0.19 mm/year
- Hyperopes: 0.15 mm/year
Chamberlain et al. 2021 propose that the success of myopia progression control should be measured by how much axial length progression can be slowed to approach the normal progression in emmetropic children of the same age. Said differently, the physiological emmetropic growth curve defines a target for myopia management: to slow down excessive axial length progression to the age-normal physiological growth observed in emmetropic children.
Hence, a successful intervention for a child under 10 years old, typically showing axial elongation greater than 0.3 mm per year without treatment, would have a clinically meaningful outcome if annual progression can be slowed to less than 0.3 mm. It would be an exceptional outcome if annual axial length progression could be slowed to less than 0.2 mm, the rate at which typical emmetropic children of the same age progress per year.
In myopic children older than 10 years, who typically show an average axial elongation of 0.2 mm without treatment, a clinically meaningful outcome of myopia intervention would be if axial length progression can be slowed to less than the untreated average. Slowing axial length elongation to 0.1 mm per year or less would be an exceptional outcome for adolescents, as typical emmetropes of the same age demonstrate this axial elongation rate.
Emmetropic axial length progression is a target for myopia progression control. Physiological axial length progression changes with age, with older children progressing slower than younger children. Thus, intervention goals differ depending on the child’s age. Finally, eye care professionals must educate parents that not all children are average, and their child may be a faster progressor.
Best professional regards,
Dwight H. Akerman, OD, MBA, FAAO, FBCLA, FIACLE
Chief Medical Editor