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Paul Gifford, Pauline Kang, Vinod Masseedupally, Michael Tran, Courtney Priestley; Can orthokeratology lens design be modified to alter peripheral refraction?. Invest. Ophthalmol. Vis. Sci. 2019;60(9):6327. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate whether the refractive treatment zone diameter (TZD) induced by overnight orthokeratology (OK) lens wear can be reduced by altering OK lens parameters, and the effect this has on peripheral refraction (PR).
OK contact lenses (Capricornia, Brisbane) were empirically fit in standard commercial design (control) and modified (test) designs for overnight wear only to correct myopia. Back optic diameter was reduced by 0.5mm in test compared to control lenses and back-optic zone asphericity and radius of the first peripheral curve were altered to maintain equivalent sag height. Order of lens wear was randomly assigned with a minimum 1-week washout period (no lens wear) between designs. Participants and examiners were masked to the order of lens wear. TZD and corneal refractive power profiles in the horizontal meridian calculated from corneal topography (Medmont E300), and peripheral refraction (NVision-K5001) were measured at baseline (BL) and after lens removal in the morning after 7 nights of lens wear (Day-7). Linear mixed model tests were employed to compare changes from baseline, with a critical p-value of 0.05.
One subject was excluded due to poor response from OK lens wear leaving sixteen subjects (aged 22 to 27 years) for analysis. By Day-7 horizontal TZD was 0.93±0.88mm smaller with test vs control lenses (p<0.001). TZD decentered temporally by 0.50±0.53 in test eyes and 0.61±0.52mm in control eyes. By Day 7 both OK designs induced an increase in corneal power relative to BL at locations 3.5, 3 and 2.5mm temporal and 2, 2.5 and 3mm nasal, representing a range of 1.5-3mm on either side of the TZ centre (p<0.001). Test lenses induced greater increase in corneal refractive power relative to the corneal apex at the 2, 2.5 and 3mm nasal locations (p<0.01) but not temporal locations. By Day-7 the control design induced a change in PR at central, temporal 20, 30, 35 degrees and nasal 10 and 20 degrees locations (p<0.006). There was no significant difference in effect on PR between test and control lenses at any location.
The TZD induced by overnight OK lens wear can be reduced through controlling lens design parameters. Reducing the TZD resulted in greater increase in mid-peripheral corneal refractive power along the horizontal nasal meridian, but failed to translate into a significant difference in change to PR profile between test and control designs.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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