One‐year results of the Variation of Orthokeratology Lens Treatment Zone (VOLTZ) study : a prospective randomised clinical trial

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.