Abstract
Purpose
To determine whether orthokeratology (OK) induced treatment zone (TZ) diameter can
be reduced by altering OK lens design, and if so the impact of modifying TZ diameter
on relative peripheral refraction (RPR).
Methods
16 subjects (mean age 23.4 ± 1.5 years; 8 female) completed the study. Standard (Control)
OK lens design (PJ, Capricornia, Australia) or a modified version (Test) where the
back optic zone diameter was reduced, and back optic zone asphericity and intermediate
lens curves were altered, were worn overnight only for 7-nights in a randomised double
masked order, with a minimum 1-week wash out (no lens wear) between lens designs.
Full correction of refractive error was targeted. Refraction; best corrected visual
acuity (BCVA); RPR (Shin-Nippon NVision-k 5001) along the horizontal and vertical
meridians; and corneal topography (Medmont E300) were measured before starting lens
wear and in the morning after lens removal after the seventh night of lens wear for
both lens designs. TZ diameter and decentration was calculated from corneal topography.
Results
After 7-nights of wear both lens designs created -2.00D refraction effect with no
significant difference in refractive effect or change to BCVA between the designs.
The Test design created a significantly smaller horizontal (4.78 ± 0.37 vs 5.70 ± 0.37 mm,
p < 0.001) and vertical (5.09 ± 0.51 vs 5.92 ± 0.51 mm p < 0.001) TZ diameter. The
TZ was decentered inferior temporal with no significant difference between designs.
There was no significant difference between the lens designs in RPR along the horizontal
and vertical meridians at any measurement period.
Conclusions
OK induced TZ diameter can be reliably reduced by altering OK lens design without
detrimentally effecting lens centration or refractive effect. Reducing TZ diameter
did not alter RPR, though measurement artifacts could be responsible for masking an
effect. Longitudinal studies are needed to assess whether smaller TZ OK lens designs
increase efficacy for slowing progression of myopia.
Keywords
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Article info
Publication history
Published online: November 24, 2019
Accepted:
November 13,
2019
Received in revised form:
November 13,
2019
Received:
September 14,
2019
Identification
Copyright
© 2019 Published by Elsevier Ltd on behalf of British Contact Lens Association.
