Prediction of Orthokeratology Lens Decentration with Corneal Elevation

SIGNIFICANCE: Lens decentration is common and unavoidable to some extent during ortho-k treatment. By using a simplified method, we are able to predict the magnitude and direction of ortho-k lens decentration, which provides useful insights in screening for ideal ortho-k candidates and to make a quick decision when decentration happens. PURPOSE: The aim of this study was to investigate the influence of corneal elevation asymmetry on ortho-k lens decentration. METHODS: Thirty-six eyes of 36 subjects were fitted with four-curve reverse geometry ortho-k contact lenses. Corneal topography was collected before and 1 month after ortho-k lens wear. The difference in corneal elevation at the 8-mm chord of the respective two principal meridians of corneal astigmatism was calculated. Vector analyses were performed on these differences to calculate the magnitude and direction of a vector (corneal asymmetry vector). The relationship between the angle and magnitude of corneal asymmetry vector and lens decentration was analyzed. RESULTS: Baseline refractive sphere and cylinder for the 36 tested eyes were -2.84 +/- 1.04 diopters (D) (range, -4.75 to -1.00 D) and -0.21 +/- 0.28 D (range, -1.00 to 0 D), respectively. The mean magnitude of lens decentration was 0.72 +/- 0.26 mm (0 to 1.34 mm). For overall displacement, inferotemporal decentration was the most common as observed in 24 eyes (67%). The mean angle of the corneal asymmetry vector (202 +/- 39 degrees) was significantly correlated to the mean angle of lens decentration (200 +/- 39 degrees) (r = 0.76, P <.001). The magnitude of corneal asymmetry vector significantly contributed to the magnitude of lens decentration (standardized beta = 0.448, P =.002) whereas the other tested variables did not affect lens decentration (all P > .05). CONCLUSIONS: Lens decentration is a common phenomenon in ortho-k that mostly happens toward the inferotemporal quadrant of the cornea. The magnitude and direction of lens decentration are predetermined by paracentral corneal asymmetry. Copyright (C) 2017 American Academy of Optometry