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Vinod Kumar Maseedupally, Pauline Kang, Mark Bae, Mikha Liem, Paul Gifford, Helen A Swarbrick; Corneal refractive power changes during orthokeratology using different contact lens designs. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):6089.
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To compare corneal refractive power (CRP) changes in the horizontal and vertical meridians of the para-central region induced by three orthokeratology (OK) lens designs worn overnight only for 2 weeks.
19 myopic subjects (6M, 13 F, age: 21 to 41 years) enrolled in this two phase prospective study. In phase 1, subjects wore BE OK lenses (Capricornia Contact Lens, Australia) in both eyes for 2 weeks. In phase 2, one eye was randomly chosen to wear a Contex lens (Contex, USA) and the contralateral eye a Paragon CRT lens (Paragon Vision Sciences, USA) for 2 weeks. Corneal topography (Medmont E300, Australia) was obtained at baseline and after 14 nights of lens wear in both phases. A custom written MATLAB program was used to determine CRP along horizontal and vertical meridians in 0.5mm increments from the vertex normal (VN) up to 8mm diameter. Linear mixed model analysis was used to detect differences between lens designs worn in the same eye in terms of CRP change from baseline in the para-central region (annular region from 2.5 to 3.5mm from VN) along each meridian.
There was a significant difference in CRP change between BE and Contex OK lenses along the horizontal meridian (p<0.001). Analysis of individual locations revealed a reduced CRP at 2.5mm nasal (p=0.002) and an increased CRP at 3.0mm (p<0.001) and 3.5mm (p=0.001) temporal with BE lenses. In the vertical meridian, no difference was found in the overall CRP change in the para-central region between the two lens designs (p=0.542). Comparisons between BE and Paragon CRT lenses showed no significant differences in CRP change between the lens designs in either horizontal (p=0.329) or vertical (p=0.748) meridians. Averaging over lens designs the reduction in central CRP (-1.9D) was greater than the increase in para-central CRP (+0.4D).
Although significant differences were found in CRP change between BE and Contex OK lenses at three locations along the horizontal meridian, these differences were not clinically significant. No significant differences were found between BE and Paragon CRT lenses in either meridian. We conclude that the three lens designs used in this study induce similar corneal refractive effects. We did not find a 1:1 relationship between central reduction and para-central increase in CRP as has been reported by others.
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