Abstract
PurposeTo present the 1‐year results of the Variation of Orthokeratology Lens Treatment Zone (VOLTZ) Study, which aims to investigate the myopia control effect of orthokeratology (ortho‐k) lenses with different back optic zone diameters (BOZD).MethodChildren, aged 6 to <11 years, having myopia −4.00 D to −0.75 D, were randomly assigned to wear ortho‐k lenses with 6 mm (6‐MM group) or 5 mm (5‐MM group) BOZD. Data collection included changes in refraction, vision, lens performance and binding, ocular health conditions, axial length and characteristics of the treatment zone (TZ) area.ResultsThe 1‐year results of 34 and 36 subjects (right eye only) in the 6‐MM and 5‐MM groups, respectively, are presented. No significant differences in baseline demographics were found between the groups (p > 0.05). The first‐fit success rates, based on satisfactory centration at the 1‐month visit, were 100% and 94% respectively. Horizontal TZ size was 0.92 mm and 0.72 mm smaller in the 5‐MM group at the 6‐month and 12‐month visits, respectively (p < 0.05). At the 12‐month visit, no significant between‐group differences were found in the incidence of corneal staining (low grade only), lens binding and visual performance (all p > 0.05). Axial elongation was slower in the 5‐MM group (0.04 ± 0.15 mm) than the 6‐MM group (0.17 ± 0.13 mm) (p = 0.001). A significant positive correlation was observed between the horizontal TZ size and axial elongation (r = 0.36, p = 0.006).ConclusionClinical performance of the two ortho‐k lenses was similar, indicating that a smaller BOZD (5 mm) did not affect lens performance or ocular integrity. However, a smaller BOZD led to a reduced TZ, with retardation of axial elongation by 0.13 mm compared to conventional 6 mm BOZD ortho‐k lenses after one year of lens wear.
Highlights
The prevalence of myopia in adults is higher in East Asian countries compared to other regions.[1]
This paper presents first year results of a longitudinal study comparing treatment effects of 6 and 5 mm back optic zone diameters (BOZD) ortho-k lenses and shows that reducing treatment zone (TZ) is effective in increasing the effectiveness of myopia control in terms of axial elongation during the first six months
The first-fit success rates of the two lens designs were comparable: 100% and 94% 6-MM and 5-MM subjects achieved successful lens fit at the 1-month visit, which was comparable to the 95% reported by Tan et al.[37] using the same brand of 6 mm BOZD lenses
Summary
The prevalence of myopia in adults is higher in East Asian countries compared to other regions.[1] This ethnic difference in myopia incidence is even more evident in the younger generation.[2] Previous studies have reported a high proportion of myopia in 5–8 years old children in Japan (7 years old: 71.9%),[3] Taiwan (7 years old: 25.4%)[4] and Hong Kong (6–8 years old: 25.0%),[5] compared with those of similar ages elsewhere, including Australia (6.7 years old: 1.4%)[6], the USA (5–7 years old: 14.7%)[7] and Poland (5–7 years old: 18%).[8] The increasing prevalence of myopia worldwide[9,10] and the potential risk of developing sight-threatening conditions[11,12] in highly myopic eyes has attracted attention to the importance of retarding myopia progression in children, thereby. Faria-Ribeiro et al.[25] reported significantly higher 4th order spherical aberration and peripheral refraction (more myopic defocus) in subjects with larger pupils, which may be due to a greater area being exposed to higher order aberrations and peripheral refraction
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