Corneal Elevation, Power, and Astigmatism to Assess Toric Orthokeratology Lenses in Moderate-to-High Astigmats

Objectives: Fitting philosophies for toric orthokeratology are based on elevation or corneal astigmatism, but it is unclear which is more effective. The purpose of this analysis was to further understand corneal shape and the relationship between peripheral elevation and central astigmatism in moderate-to-high astigmats. Methods: Corneal tomography was measured three times on the right eyes of 25 moderate-to-high refractive myopic astigmatic adults. Corneal astigmatism and elevation were calculated at 4-, 6-, and 8-mm chords. Subjects were fitted with toric orthokeratology lenses following the manufacturer's guidelines based on elevation. Twenty subjects completed 10 days of wear. A masked examiner assessed movement and centration via slitlamp videos and quantified treatment zone and decentration from tangential power difference tomography maps. Correlations between variables were assessed. Results: Average corneal astigmatism was 2.20 +/- 0.70 DC and peripheral elevation was 50.88 +/- 18.92 mu m and they were strongly correlated (4 mm R-2=0.96, 6 mm R-2=0.92, 8 mm R-2=0.86, all P<0.001). Each diopter of astigmatism equated to 25 mu m of elevation at an 8-mm chord. Via slitlamp, average treatment zone area was 12.73 +/- 4.62 mm(2) and 13 lenses decentered. From tomography, average treatment zone area was 7.16 +/- 2.56 mm(2) and 17 were decentered. Tomography treatment zone area was negatively correlated with central corneal astigmatism (R-2=0.60) and elevation at an 8-mm chord (R-2=0.64, both P<0.001). Conclusions: For tomography images, central corneal astigmatism was highly correlated with peripheral elevation and may be a more expedient measure for clinical use. Treatment area decreased as corneal astigmatism and elevation increased.

Automated summary

The study on corneal shape and the relationship between peripheral elevation and central astigmatism in astigmatic individuals found a high correlation between central corneal astigmatism and peripheral elevation, suggesting that central corneal astigmatism may be a more expedient measure for clinical use. Additionally, the treatment area decreased as corneal astigmatism and elevation increased.