August 1, 2024
By Erin Lam, BOptom
Photo Credit: Getty Images
Orthokeratology corrects myopia by flattening the central cornea curvature while steepening the paracentral cornea, with the additional benefit of controlling myopia progression. Guo et al. 2023 report the two-year results of the Variation of Orthokeratology Lens Treatment Zone (VOLTZ) study, which compares the association between axial elongation (AE) and the OrthoK treatment zone (TZ).
Participants included 45 children of Chinese ethnicity, aged 6-11, with mild-moderate myopia and no history of myopia control therapy. They were randomly assigned either a 5mm or 6mm back optic zone diameter (BOZD) OrthoK lens.
After two years, the OrthoK lenses with a smaller BOZD created a smaller TZ diameter, resulting in less AE (0.20mm) but no significant difference in choroidal thickness. The smaller BOZD lenses did not significantly affect visual performance or cause any significant visual signs or symptoms compared to conventional OrthoK construction. However, similar associations were not observed in those with higher refractive error who wore the 5mm OrthoK design. This is thought to be due to a greater change in aberrations.
To conclude, Guo et al. 2023 suggest that the 5mm BOZD lenses lead to a slower AE after two years of lens wear compared to the conventional 6mm BOZD lenses. There was a similar clinical performance with no significant effect on ocular integrity.
Abstract
Variation of Orthokeratology Lens Treatment Zone (VOLTZ) Study: A Two-Year Randomized Clinical Trial
Biyue Guo, Sin Wan Cheung, Randy Kojima, Pauline Cho
Purpose: To compare axial elongation (AE) and treatment zone (TZ) characteristics in children wearing 6mm or 5mm back optic zone diameter (BOZD) orthokeratology (ortho-k) lenses over 2 years.
Methods: Forty-five (6 to < 11 years of age) myopic (−4.00 to −0.75 D) children of Chinese ethnicity were randomly assigned to use the two different lens designs (23 and 22 wore the 6 and 5mm lenses, respectively). Data collection was performed at baseline and every 6 months after commencing lens wear.
Results: After 24 months, subjects wearing lenses with a 5mm BOZD achieved smaller TZ diameter (horizontal: 2.69±0.28 vs. 3.84±0.39mm; vertical: 2.65±0.22 vs. 3.42±0.34mm, p<0.001) and less AE (0.15±0.21 vs. 0.35±0.23, p=0.005) compared to those using the 6mm design, with no difference in choroidal thickness (ChT) changes (p=0.93). A significant increase in ChT, using pooled data analysis, was noted at the 6-month (11.8±19.77μm, p<0.001) and 12-month (12.0±23.7μm, p=0.004) visits, compared to baseline, indicating a transient change in ChT. Significant associations were noted, using linear mixed models, between AE and the TZ diameters (p<0.003) after adjusting for baseline data. A very weak association was found between ChT changes and AE, with the effect size close to zero.
Conclusions: Smaller BOZD ortho-k lenses resulted in a smaller TZ diameter, which was associated with less AE after 2 years of treatment. The changes in ChT played a very weak role, suggesting that other factors may contribute more to the reduced AE in subjects wearing lenses having a smaller BOZD.
Key points: Orthokeratology lenses with smaller back optic zone diameters resulted in less axial elongation over two years compared to lenses with larger optical zones.
Smaller back optic zone diameter orthokeratology lenses resulted in smaller treatment zone diameters, which was associated with less axial elongation.
Changes in sub-foveal choroidal thickness were unaffected by the treatment zone size over time and, hence, had limited effect on axial elongation.
Guo, B., Cheung, S. W., Kojima, R., & Cho, P. (2023). Variation of Orthokeratology Lens Treatment Zone (VOLTZ) Study: A 2‐year randomised clinical trial. Ophthalmic and Physiological Optics, 43(6), 1449-1461.
DOI: https://doi.org/10.1111/opo.13208
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Erin Lam is an Australian optometrist who graduated from Deakin University with a Master of Optometry. She is currently a Manager of Daily Operations and Staff Optometrist at the Australian College of Optometry in Melbourne. She has a strong interest in contact lenses and myopia control. |
