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Title: One‐year results of the Variation of Orthokeratology Lens Treatment Zone (VOLTZ) study : a prospective randomised clinical trial
Authors: Guo, B 
Cheung, SW 
Kojima, R
Cho, P 
Issue Date: Jul-2021
Source: Ophthalmic and physiological optics, July 2021, v. 41, no. 4, p. 702-714
Abstract: Purpose: To present the 1-year results of the Variation of Orthokeratology LensTreatment Zone (VOLTZ) Study, which aims to investigate the myopia controleffect of orthokeratology (ortho-k) lenses with different back optic zone diameters(BOZD).
Method: Children, aged 6 to <11 years, having myopia −4.00 D to −0.75D, were randomly assigned to wear ortho-k lenses with 6 mm (6-MM group) or5 mm (5-MM group) BOZD. Data collection included changes in refraction,vision, lens performance and binding, ocular health conditions, axial length andcharacteristics of the treatment zone (TZ) area.
Results: The 1-year results of 34 and 36 subjects (right eye only) in the 6-MMand 5-MM groups, respectively, are presented. No significant differences in base-line demographics were found between the groups (p > 0.05). The first-fit successrates, 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-MMgroup 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 incidenceof corneal staining (low grade only), lens binding and visual performance (allp > 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 cor-relation was observed between the horizontal TZ size and axial elongation(r = 0.36, p = 0.006).
Conclusion: Clinical performance of the two ortho-k lenses was similar, indicat-ing that a smaller BOZD (5 mm) did not affect lens performance or ocular integ-rity. However, a smaller BOZD led to a reduced TZ, with retardation of axialelongation by 0.13 mm compared to conventional 6 mm BOZD ortho-k lensesafter one year of lens wear.
Keywords: BOZD
Myopia control
Treatment zone
Publisher: Wiley-Blackwell
Journal: Ophthalmic and physiological optics 
ISSN: 0275-5408
EISSN: 1475-1313
DOI: 10.1111/opo.12834
Rights: © 2021 The Authors. Ophthalmic and Physiological Optics published by John Wiley & Sons Ltd on behalf of College of Optometrists.
This is an open access article under the terms of the Creative Commons Attribution License (, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
The following publication Guo, B, Cheung, SW, Kojima, R, & Cho, P. One-year results of the Variation of Orthokeratology Lens Treatment Zone (VOLTZ) Study: a prospective randomised clinical trial. Ophthalmic Physiol Opt 2021; 41: 702– 714 is available at
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