A Study of The Repeatability of Peripheral Refraction Measurements and the Effects of Spherical Soft Contact Lens Wear (SSCL)

Abstract

Purpose:: To examine the reliability of peripheral refraction measurements using Grand Seiko WR-5100K autorefractor and the effect of SSCL wear on peripheral refractions. Speculation that peripheral refractive errors may underlie myopia development and progression motivated this study.

Methods:: Peripheral refractive errors were measured out to 40 degrees eccentricity on fourteen eyes of 8 young adult subjects (mean age: 24.3yr; mean RE: -3.38D), using Grand Seiko WR-5100K autorefractor. For off-axis locations, subjects viewed one of a series of red LEDs mounted on a bar at 50cm and spaced at 5-degree intervals; they were switched on in turn. Measurements were made under very low room illumination; mydriatic drugs were not used. Two sets of measurements were obtained on the same day (morning and afternoon), for both uncorrected and SSCL corrected conditions. Equivalent sphere values (ES) were subject to multivariate regression (y=ax²+bx+c; critical p-value of 0.05) and descriptive analyses, adjusting for within-subject correlation, time of day variation, inter-ocular variability, and SSCL correction.

Results:: On average, ES values became more hyperopic with increasing eccentricity. For eccentricities within ±25 degrees, differences between predicted and recorded ES values, were neither clinically nor statistically significant after adjusting for possible confounders. However for eccentricities greater than 25 degrees, both within- and between-subject variations in measurements increased significantly, pupil size constraints and CL decentration at extreme gazes being likely contributing factors. SSCL wear significantly affected the value of the primary coefficient (a), in the model (p=0.006; a=-0.0003; 95% CI: -0.0055, -0.0013).

Conclusions:: The Grand Seiko WR-5100K autorefractor with add-on fixation bar allowed reliable measurement of peripheral refractive errors out to 25 degrees eccentricity. The repeatability of measurements at greater eccentricities could be improved with the use of 2.5% phenylephrine, a mydriatic drug, and tighter fitting SCLs. SSCLs significantly affected peripheral refractive errors. The effects of other soft CL designs on peripheral refractions are likely to be different and warrant further research.

Keywords: myopia • clinical (human) or epidemiologic studies: systems/equipment/techniques • contact lens