PURPOSE. To investigate thickness profile changes of the corneal epithelium and Bowman's layer at the vertical and horizontal meridians with overnight myopia orthokeratology (OK) lenses.METHODS. Twenty subjects (age range: 19-33 years) wore reverse-geometry rigid gas-permeable OK lenses in both eyes for 30 days. Before lens wear and after 1, 7, and 30 days of overnight lens wear, evaluation of lens fitting, visual acuity examination, corneal topography, and ultra-high resolution optical coherence tomography (UHR-OCT) were performed. The central, midperipheral, and peripheral cornea were imaged in both the horizontal and vertical meridians. Custom software was produced to acquire the thickness profiles of the epithelium and Bowman's layer. RESULTS.Unaided visual acuity and refraction were improved significantly after OK lens wear. The central corneal epithelium thinned in the horizontal and vertical meridians after one night of lens wear (P < 0.05). In the horizontal meridian, the epithelium thickened at the temporal and nasal midperipheries (P < 0.05), while the superior midperipheral epithelium thinned in the vertical meridian. There were no changes in the thickness profile of Bowman's layer during the study period.CONCLUSIONS. Overnight wear of OK lenses caused the central corneal epithelium to thin in both the vertical and horizontal meridians, while the midperipheral nasal and temporal epithelium became thicker and the superior midperipheral epithelium became thinner. The thickness of the central or midperipheral Bowman's layer in either meridian did not change. Improved vision acuity after overnight OK lens wear can be attributed to changes in the corneal epithelium and not Bowman's layer. (Invest Ophthalmol Vis Sci. 2013;54:691-696) DOI:10.1167/iovs.12-10263 O rthokeratology (OK) is used to temporarily reduce the refractive error in myopic patients by the programmed application of specially designed rigid contact lenses.1,2 The improvement of uncorrected visual acuity and reduction in myopia are attained by flattening and thinning of the central cornea. OK lenses for myopia provide reliable refractive correction for up to À4.5 diopters (D) on lens removal. [3][4][5] With the development of higher gas-permeable lens materials, overnight OK lens has come into greater use as a treatment modality to correct refractive error. [6][7][8] Previous studies have reported the time course of refractive and topographic thickness changes of the cornea and its sublayers in myopia OK lens wearers. [9][10][11] In an early study, Swarbrick et al., using a modified optical pachymeter, found central epithelial thinning and midperipheral corneal thickening after reverse-geometry lens wear.9 Albarbi et al. obtained similar results using an overnight OK lens-wearing modality. 10Wang et al. used optical coherence tomography (OCT) to measure the topographic thickness of the cornea and epithelium after one night of OK lens wear. 11 However, all of these studies were focused on thickness changes of the total cornea and the epitheliu...

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