Risk Factors of Poor Fitting for a New Orthokeratology Lens: a case control study

Background: The purpose of this study is to compare differences between the good and poor fitting group in Orthokeratology patients and look for risk factors of poor fitting. Methods: A total of 382 eyes (216 patients) were retrospectively analyzed. Eyes being enrolled were 41 (24 patients) and 36 (22 patients) in the good fitting and poor fitting group. Re-fitting time, reason, lens parameters before and after re-fitting were assessed in the poor fitting group. Patients information, refractive outcomes, topography and lens parameters were compared between the two groups. Risk factors and diagnostic value of each risk factor were discovered for poor fitting. Results: (1) There were no significant differences in age ( p =0.209), sex ( p =0.376) and eye ( p =0.649) between the two groups; (2) The median re-fitting time was 6.5 weeks (range: 2-28 weeks). Main reasons for re-fitting were lens binding and unsatisfactory uncorrected visual acuity; (3) After re-fitting, lens type ( p =0.415), toric value ( p =0.747), and alignment curve (AC) ( p =0.050) remained unchanged, but lens diameter decreased (10.64±0.20mm vs 10.53±0.24mm, p =0.002), the proportion of lens with a diameter less than 10.6mm increased ( p =0.020); (4) Spherical refraction ( p =0.004), refractive astigmatism ( p <0.001), flat k ( p <0.001), steep k ( p <0.001), corneal astigmatism ( p =0.048), and AC ( p <0.001) differed significantly between the two groups; (5) Steep K (B=-0.960, p =0.001), refractive astigmatism (B=1.646, p =0.015) and lens diameter (B=-3.744, p =0.040) were independent risk factors for poor fitting. Steep k has the most valuable diagnostic value, with a cut off value of 44.69 (sensitivity 0.69, specificity 0.85). Conclusions: The main reasons for re-fitting were lens binding and unsatisfactory uncorrected visual acuity. Steep K, refractive astigmatism and lens diameter were independent risk factors of poor fitting. The strongest diagnostic value was steep K. Patients with a steep k<44.69 are good candidate for lens fitting . When fitting this brand of Ortho-k lens, the lens diameter should not be too large.