Repeatability of relative peripheral refraction in untreated and orthokeratology-treated eyes

To determine the repeatability of relative peripheral refraction (RPR) measurements using an open-view automatic refractor in untreated and orthokeratology (ortho-k)-treated eyes of children.

Cycloplegic central (CR) and peripheral refraction (PR) across the central 60° horizontal field at 10° intervals were measured in children (6-9 years) using a Shin-Nippon NVision K5001 autorefractor. In experiment 1, measurements were repeated at the same visit for 59 untreated (right) eyes, whereas in experiment 2, measurements were repeated at the same visit and another visit (1-2 weeks apart) for 24 ortho-k-treated (right) eyes to determine the intra- and intervisit repeatability, respectively. Measurements were transposed into M, J0, and J45 vectors, and RPR were calculated by subtracting central refraction from PR values. Intra- and intervisit differences and coefficients of repeatability (COR) of RPR were determined.

The mean intravisit differences in RPR for all three vectors were ≤0.05 D for untreated eyes, and both intra- and intervisit differences in RPR were ≤0.32 D for ortho-k-treated eyes. No significant intra- and intervisit differences in RPR were found at any field angle in this study. COR of measurements were <±0.71 D in the untreated eyes, and <±1.25 D (intravisit) and <±3.00 D (intervisit) in ortho-k-treated eyes. The COR increased with field angles in all situations and were greater in ortho-k-treated than in untreated eyes. In ortho-k-treated eyes, intervisit COR of measurements beyond central 40° field were larger than the intravisit COR.

The mean intra- and intervisit differences of RPR measurements were small in both untreated and ortho-k-treated eyes. Variability of PR measurements increased with field angle and with ortho-k treatment.