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P. Gifford, W. Au, B. Hon, A. Siu, P. Xu, H. A. Swarbrick; Mechanism for Corneal Reshaping in Hyperopic Orthokeratology - Suction or Molding?. Invest. Ophthalmol. Vis. Sci. 2008;49(13):4857. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate the mechanism underlying hyperopic orthokeratology (OK) by comparing the short-term clinical effect of lenses before and after central lens fenestration.
Twelve subjects (age 21 to 24 years) were fitted with rigid hyperopic OK lenses (Capricornia Contact Lens Pty Ltd) in one eye only. The fellow eye acted as a non lens wearing control. Lens specifications were matched to provide the same post lens tear film profile in all subjects. Non-fenestrated lenses were worn in the open eye for 1 hour and in the closed eye for 4 nights. Subjective BVS refraction and corneal topography (Medmont E300) were measured at baseline, after 1hr lens wear, and within 1hr of waking on Days 1 and 4 of overnight lens wear. The lenses were then sent for three 0.75mm fenestrations within the central optic zone. The lens wearing and measurement procedures were then repeated. RE-ANOVA with post-hoc paired t-tests was employed to compare changes from baseline.
BVS refraction changed after 1hr lens wear (0.46±0.16D), increasing to 0.81±0.16D by Day 4 with non-fenestrated lenses, and 0.38±0.11D increasing to 0.60±0.10D once fenestrations were applied (p<0.05). Central corneal curvature steepened after 1hr (0.41±0.18D), increasing to 0.72±0.17D by Day 4 with non-fenestrated lenses, and 0.34±0.12D increasing to 0.78±0.16D once fenestrations were applied (p<0.05). Average combined paracentral curvature flattened after 1hr (-0.33±0.05D), increasing to -0.62±0.06D by Day 4 with non-fenestrated lenses, and -0.37±0.06D increasing to -0.61±0.06D once fenestrations were applied (p<0.01). There were no statistically significant differences between the lens types in either BVS refraction or corneal curvature changes.
A hyperopic OK effect was established in as little as 1 hour with increased effect with longer lens wearing time. Central fenestrations did not alter the clinical outcomes, indicating that lens compression in the paracentral region as opposed to central post lens tear film suction is the primary mechanism behind the hyperopic OK clinical effect. Further research is indicated to establish optimum lens curvature profiles within the compressive paracentral region to maximise the hyperopic OK treatment effect.
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