Fig 1.
Measurement of treatment zone size.
Treatment zone was derived from differential tangential map between baseline and post-OK fitting, which was equivalent to central flattening area surrounded by mid-peripheral annular ring of corneal steepening. Horizontal and vertical diameters of treatment zone were indicated by the lines with arrow heads, and treatment zone was demarcated by the blue circle of best fit indicated by the larger arrow head symbols. Treatment zone diameter and area were measured using pixel length and area from Image J software, which was converted to the mm using the scale provided by in the corneal topography.
Table 1.
Changes in refractive and topographic indices.
Fig 2.
Representative corneal epithelial thickness and topography during orthokeratology.
The corneal epithelial thickness maps are divided into a total of 17 sectors: a central 2 mm diameter zone, eight paracentral zones within an annulus between the 2 and 5 mm diameter rings, and eight mid-peripheral zones within an annulus between the 5 and 6 mm diameter rings. The epithelial thickness map shows central compression area surrounded by annular mid-peripheral thickening area and they seem to fit to tangential topographic images. (A) Baseline epithelial thickness, (B) post-OK epithelial thickness map and (C) post-OK tangential topography.
Table 2.
Corneal thickness changes before and after orthokeratology.
Fig 3.
Topographic corneal epithelial thickness map before and after orthokeratology.
The corneal epithelium thinned from the center to the paracenter, and the mid-peripheral epithelium thickened. There was more thinning of the temporal and inferior zones compared with the nasal and superior zones of the paracenter, with further thickening in the nasal zone compared with the temporal zone in the mid-periphery. *P<0.05, **P<0.01, and ***P<0.001.
Table 3.
Corneal thickness change in 3 groups, divided by duration of orthokeratology.
Table 4.
Simple regression between myopia correction and various factors.
Fig 4.
Relationship between changes in refractive error predicted by Munnerlyn’s formula and refractive changes observed after orthokeratology.
Changes in central epithelial thickness and treatment zone diameter are substituted for ablation depth and diameter, respectively in Munnerlyn’s formula. The red line represents equality between the measured refractive change and the predicted refractive change.