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P. Gifford, A. Alharbi, H. Swarbrick; Corneal Thickness Changes in Overnight Hyperopic Orthokeratology. Invest. Ophthalmol. Vis. Sci. 2009;50(13):5629.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate the time course of corneal thickness changes in overnight hyperopic orthokeratology (OK) lens wear, over a 4-day lens-wearing period.
Fourteen subjects (age 20 to 37 years) were fitted with bi-aspheric rigid lenses designed for hyperopic OK (Capricornia Contact Lens), in one eye only. The fellow eye acted as a non-lens wearing control. Lenses were worn overnight only over 4 nights and changes in subjective refraction, corneal topography (Medmont E-300) and corneal thickness at central and paracentral locations (Holden-Payor optical pachometer) were measured on Days 1 and 4 after overnight lens wear, on lens removal (AM) and 8 hours after lens removal (PM). 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.
There was a significant refractive and corneal topographic effect at all visits, reaching -1.35 ± 0.68D refractive change and 1.27 ± 0.54D central corneal steepening on Day 4AM (p<0.001). Relative to baseline the total cornea thickened centrally at AM visits only, by 11.6 ± 14.7µm on Day 1AM and 13.7 ± 17.1µm on Day 4AM, and thinned paracentrally at PM visits only, by -10.0 ± 16.3µm on Day 1PM and -11.5 ± 14.6µm on Day 4PM (p<0.05). The corneal stroma thickened at AM visits only both centrally (Day 1AM, 8.6 ± 14.3µm; Day 4AM, 10.0 ± 13.2µm, p<0.05) and paracentrally (Day 1AM, 7.4 ± 17.4µm; Day 4AM, 8.9 ± 13.5µm, p<0.05). There was no significant difference from baseline in central epithelial thickness at any visit. However, there was significant paracentral epithelial thinning at AM and PM visits (Day 1AM, -5.1 ± 9.6µm; Day 1PM, -9.0 ± 11.2µm; Day 4AM, -6.1 ± 11.3µm; Day 4PM, -9.0 ± 15.1µm, p<0.05).
Stromal edema accounted for the increase in total central corneal thickness at AM visits, while reductions in paracentral corneal thickness at PM visits were explained by epithelial thinning. Corneal thickness changes in hyperopic OK were comparatively less than previously reported for myopic OK, which may explain the relatively poor clinical response that has been reported for hyperopic OK.
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