Vertical and Horizontal Thickness Profiles of the Corneal Epithelium and Bowman's Layer after Orthokeratology

Abstract

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...

Semiautomated SD-OCT Measurements of Corneal Sublayer Thickness in Normal and Post-SMILE Eyes

“…This was well in agreement with previous high-resolution SD-OCT-based studies, which reported normal central ET readings ranging from 48.3 to 58.6 mm. 5,9,14,17,[26][27][28][29][30][31][32][33][34][35] In our study, the normal epithelial profile along the central 5-mm horizontal meridian presented homogeneously and symmetrically. In other reports, ET along the horizontal meridian seemed to increase slightly from the center toward the corneal periphery.…”

“…In other reports, ET along the horizontal meridian seemed to increase slightly from the center toward the corneal periphery. 25,31,35 In these studies, however, the entire epithelial profile was assessed and epithelial thickening was most pronounced outside of the central 5-mm zone in the vicinity of the corneal limbus.…”

The Use of Bowman's Layer Vertical Topographic Thickness Map in the Diagnosis of Keratoconus

“…Details of the imaging and image analysis techniques were described in previous reports. 15–17 Briefly, each subject was asked to look at a central fixation target to capture a vertical 2D image of central cornea centered on the corneal vertex. The presence of a visible specular reflection confirmed that the OCT scanning probe was perpendicular on the cornea.…”

“…15–17 In order to further validate the imaging technique, a validation and repeatability experiment was carried out. In our experiment, 8 eyes of 4 normal subjects received corneal marking 3 mm superior and 3 mm inferior to visual axis using a slit lamp and a marking pen (Devon surgical marker, Tyco Healthcare, Mansfield, Massachusetts, USA).…”

OCT corneal epithelial topographic asymmetry as&nbsp;a sensitive diagnostic tool for early and advancing keratoconus

“…One possibility lies in the fact that irregular epithelial thickness distribution can “compensate” for underlying irregular stromal distribution,26,27 and thus may mask topographic and tomographic results, particularly in early stage KCN investigation. We believe therefore that epithelial thickness imaging may be extremely helpful in KCN investigation by revealing the accentuated stromal irregularities that may not be detected by traditional corneal topography.…”