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Study: Manipulating ortho-K lenses to customize refraction may be difficult
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A recently published study determined that changing orthokeratology lens parameters caused significant changes in peripheral refraction, corneal topography and corneal surface aberrations, and as such, attempting to customize refraction and topography through manipulation of the lens is a difficult task.
Subjects included in the study were fitted with standard orthokeratology (ortho-K) lenses that were worn overnight for 2 weeks. Measurements for peripheral refraction, corneal topography and corneal surface aberrations were taken at baseline and after 14 nights of wear.
After a 2-week washout period, subjects were refitted with another set of lenses where one eye was randomly assigned to wear an ortho-K lens with a smaller optic zone diameter (OZD) and the other eye a steeper peripheral tangent. Measurements were again taken at baseline and after 14 nights of wear.
Standard ortho-K lenses with a 6-mm OZD and 1/4 peripheral tangent caused a significant hyperopic shift in the central visual field, while a myopic shift was found at 35° in the nasal visual field. Significant reductions in corneal power were observed 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.
“Reducing OZD and steepening the peripheral tangent did not cause significant changes in peripheral refraction or corneal topography profiles across the horizontal meridian,” the study authors said.
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