Can manipulation of orthokeratology lens parameters modify peripheral refraction?
OBJECTIVE
To investigate changes in peripheral refraction, corneal topography, and aberrations induced by changes in orthokeratology (OK) lens parameters in myopes.


METHODS
Subjects were fitted with standard OK lenses that were worn overnight for 2 weeks. Peripheral refraction, corneal topography, and corneal surface aberrations were measured at baseline and after 14 nights of OK lens wear. Subsequent to a 2-week washout period, subjects were refitted with another set of lenses where one eye was randomly assigned to wear an OK lens with a smaller optic zone diameter (OZD) and the other eye with a steeper peripheral tangent. Measurements were taken again at a second baseline and after 14 days of overnight wear of the second OK lens set.


RESULTS
Standard OK lenses with a 6-mm OZD and 1/4 peripheral tangent caused significant changes in both peripheral refraction and corneal topography. Significant hyperopic shift occurred in the central visual field (VF) while a myopic shift was found at 35 degrees in the nasal VF. OK induced significant reductions in corneal power at all positions along the horizontal corneal chord except at 2.4 mm nasal where there was no significant change and at 2.8 mm nasal where there was an increase in corneal refractive power. A positive shift in spherical aberration was induced for all investigated lens designs except for the 1/2 tangent design when calculated over a 4-mm pupil. Reducing OZD and steepening the peripheral tangent did not cause significant changes in peripheral refraction or corneal topography profiles across the horizontal meridian.


CONCLUSIONS
OK lenses caused significant changes in peripheral refraction, corneal topography, and corneal surface aberrations. Modifying OZD and peripheral tangent made no significant difference to the peripheral refraction or corneal topography profile. Attempting to customize refraction and topography changes through manipulation of OK lens parameters appears to be a difficult task.
*PhD, FAAO School of Optometry and Vision Science, The University of New South Wales, Sydney, New South Wales, Australia.
Pauline
P
Kang
Paul
P
Gifford
Helen
H
Swarbrick
D000293:Adolescent; D000328:Adult; D003261:Contact Lenses; D019781:Corneal Topography; D057108:Corneal Wavefront Aberration / Q000503:physiopathology; D005260:Female; D006801:Humans; D006956:Hyperopia / Q000503:physiopathology / Q000517:prevention & control*; D009216:Myopia / Q000503:physiopathology / Q000517:prevention & control*; D054158:Orthokeratologic Procedures; D012029:Refraction, Ocular / Q000502:physiology; D055815:Young Adult