The Effect of Orthokeratology Lens Decentration on Ocular and Biomechanical Measurements

To investigate the effects of orthokeratology (ortho-K) lens decentration on ocular and biomechanical parameters and analyze the correlation of these parameters with decentration distance.

Thirty eyes of 30 myopic adult subjects, mean age 28.2 years who had worn ortho-K lens for two hours were recruited for this prospective study. Under both the central and eccentric lens fitting conditions, the subjects underwent two rounds of assessments with a week-long interval. The ocular parameters were measured by an IOL Master, whereas the biomechanical parameters were measured by a Corves ST. Differences between measurements were evaluated by one-way ANOVA and a post hoc test. Repeatability was analyzed based on within-subject standard deviation (Sw), repeatability coefficient (RC), intraclass correlation coefficient (ICC), and correlation of variation (CoV). Pearson correlation analysis was employed for correlation analysis.

The ocular parameters showed no significant differences, whereas among the biomechanical parameters, the biomechanical corrected intraocular pressure (bIOP) (95% CI 15.8-16.7 mmHg, 14.7-15.6 mmHg, 14.5-15.5 mmHg for baseline, central and eccentric group) and stiffness parameter at first applanation (SPA1) (95% CI 111.7-122.4, 102.3-113.0, 103.9-115.1 for baseline, central and eccentric group) showed significant changes after ortho-K. In all groups, the ocular parameters showed good repeatability with ICC values greater than 0.95 and CoV values lower than 1.3%. By contrast, the biomechanical parameters showed poor repeatability with low ICC values (ie, below 0.7) for the length of flattened cornea at the first and second applanations (A1L and A2L, respectively) and for velocity of corneal apex at the second applanation (A2V) in the baseline group; for A1L, A2L, and bIOP in the central group; and for A1L and A2V in the eccentric group. The correlation analysis showed the positive relationship in A2L between central and eccentric groups.

Ortho-K lens decentration did not influence the ocular parameters. However, the biomechanical parameters, the bIOP and SPA1 related to corneal thickness changed after ortho-K.