Abstract
PurposeTo investigate topographic changes in corneal epithelial thickness (CET) and stromal thickness following orthokeratology (OK) and to determine associated factors affecting refractive changes.MethodsThis study investigated the topographic changes in CET and stromal thickness in 60 myopic eyes that were fitted with OK lenses. CET and stromal thickness were obtained using spectral-domain optical coherence tomography (OCT) before and after OK lens wear. Changes in refractive error and corneal topography data were obtained. The correlation between refractive change and corneal thickness change, and various refractive, lens, and topographic parameters were analyzed using simple regression analysis.ResultsMean refractive error changed by 1.75 ± 0.79 diopters (D). The mean CET of the center zone (2 mm in diameter), paracenter (2 to 5 mm annular ring: 1 to 2.5 mm from center), and mid-periphery (5 to 6 mm annular ring: 2.5 to 3 mm from center) changed by -8.4, -1.4, and +2.7 μm, respectively, after OK lens wear. There was an increase of 2.0, 3.3, and 3.9 μm, respectively, in the center, paracenter, and mid-periphery of the stroma. A larger refractive correction was associated with a flatter base curve of the lens, larger decrease in the central epithelium, and smaller treatment diameter in corneal topography.ConclusionOK lenses caused the central corneal epithelium to thin while the mid-peripheral epithelium and stroma became thicker. Refractive changes during OK are associated with changes in central epithelial thickness, while stromal changes did not contribute significantly.
Highlights
Orthokeratology (OK) is used to reduce the refractive error in myopic subjects through the use of reverse-geometry rigid gas-permeable lenses, which are fitted with a base curve flatter than the central corneal curvature [1, 2]
Mean refractive error changed by 1.75 ± 0.79 diopters (D)
A larger refractive correction was associated with a flatter base curve of the lens, larger decrease in the central epithelium, and smaller treatment diameter in corneal topography
Summary
Orthokeratology (OK) is used to reduce the refractive error in myopic subjects through the use of reverse-geometry rigid gas-permeable lenses, which are fitted with a base curve flatter than the central corneal curvature [1, 2]. Recent publications have shown an inhibitory effect on the progression of myopia, and OK is receiving increased attention and becoming popular as a treatment modality for myopic children [3,4,5,6]. This technique is well established in clinical practice, limited number of studies have investigated the underlying changes in corneal tissue. Swarbrick et al found central epithelial thinning by 15.8 μm and mid-peripheral stromal thickening by 7.9 μm after 1 month of OK lens wear using an optical pachymeter [2, 7]. Previous studies have concluded that refractive changes after OK lens wear are primarily due to central epithelial thinning, but change in mid-peripheral area and stromal remodeling profiles with its role in refractive change have not been clearly addressed [13]
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