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P. Gifford, H. A. Swarbrick; Time Courses of Corneal Topographic Changes in the First Week of Overnight Hyperopic Orthokeratology. Invest. Ophthalmol. Vis. Sci. 2007;48(13):5407.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate the time course of refractive and corneal topographic changes in overnight hyperopic orthokeratology (OK) lens wear, over a 7-day lens-wearing period.
Ten subjects (age 20 to 33 years) were fitted with bi-aspheric rigid lenses designed for hyperopic OK (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 profile in all subjects. The lenses were worn overnight only over a 7-day period and changes in subjective refraction, corneal apical radius and asphericity (Medmont E-300) were measured. The dimensions of the steepened treatment area were measured from the topography plots using standard techniques. Repeated-measures ANOVA with post-hoc paired Student t-tests were employed to compare changes from baseline, with a critical p-value of 0.05.
Most refractive change occurred after the first night of hyperopic OK lens wear (1.03±0.25D), reaching 1.45±0.35D by day 7 (p<0.01). Retention of refractive effect at the end of the day improved with increasing nights of lens wear (0.64±0.25D on day 1 vs 1.18±0.44D on day 7, p<0.01). Most corneal topographic change also occurred after the first night of lens wear, with increasing effect towards day 7 (change in apical radius: -0.13±0.03mm increasing to -0.18±0.07mm, p<0.01; change in asphericity Q: -0.36±0.07 increasing to -0.52±0.18, p<0.01). Both horizontal and vertical treatment zone dimensions increased during the day on day 1 (H: +0.42±0.39mm, V: +0.42±0.41mm, p<0.05) and day 7 (H: +0.31±0.32mm, V: +0.92±0.61mm, p<0.05).
The time course of refractive and corneal topographic change in hyperopic OK is analogous to myopic OK. Most of the change in refractive and topographic variables occurs on day 1, with regression of effect during the day, but greater retention of effect by day 7. Interestingly, throughout the day while lenses were not worn, the treatment zone dimensions increased. Further research is indicated to establish the mechanisms underlying this unexpected effect, and to define the timeframe to reach the endpoint of hyperopic OK treatment.
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