Corneal Elevation Asymmetry Vector as a Predictor of One-year-averaged Orthokeratology Lens Decentration in Low Astigmats

Abstract

Significance: This study establishes a novel and practical method for locating orthokeratology lens decentration. The general lens decentration over a one-year period could be partially predicted using the corneal elevation asymmetry vector.Purpose: The predictive ability of the pretreatment corneal elevation asymmetry vector for the average orthokeratology lens decentration in Chinese myopic adolescents with low astigmatism was explored.Methods: Thirty-five myopic participants (35 eyes) were enrolled in this prospective study. The follow-up time was up to one year. Various pretreatment corneal parameters were analyzed to identify potential candidates for lens decentration prediction. An accurate and objective method was developed in MATLAB to calculate the corneal asymmetry vector, which was defined as the sum of the elevation vector at the boundary between the reverse curve and the alignment curve. The program also locates a precise lens decentration vector. The relationship between pretreatment corneal parameters and lens decentration was analyzed using linear regression.Results: Lens decentration stabilized after 1 month. The averaged lens decentration vector was calculated to indicate the general decentration situation after stabilization. The magnitude of the averaged decentration varied from 0.07 mm to 1.35 mm, with 91% measuring less than 1.0 mm. Inferotemporal decentration was the most common type (66%). Among all the pretreatment parameters, only the corneal asymmetry vector significantly correlated with the averaged lens decentration in horizontal coordinates (R=0.374, p=.027). The vertical asymmetry vector was close to significance when correlated with the vertical averaged lens decentration vector (R=0.327, p=.055). The angle of the corneal elevation asymmetry vector significantly contributed to the averaged lens decentration angle (R= 0.344, p= .043).Conclusions: The association between pretreatment corneal elevation asymmetry vector and one-year-averaged orthokeratology lens decentration may assist in fitting and understanding the performance of orthokeratology lenses.