Purpose:
Hyperopic defocus in the peripheral retina is thought to be a source of elongation of the eye and hence progression of myopia in children. The aim of this study was to determine the validity and reliability of a clinical method to evaluate off-axis (peripheral) refractive errors in myopic eyes.
Methods:
Recruited in this study were 21 adult subjects who had no ophthalmologic abnormality except for refractive errors (refractive range: -1.25 D to -12.00 D). Subjects were asked to successively look at 9- or 21-point fixation targets located within +/-30 x 30 degrees, refractive errors were measured using an open-field autorefractor FR5000 (Grand Seiko) while subjects were looking at each target. Cycloplegic eye drops were applied before the measurement. In each subject, a quadratic response surface was fitted to the data, and their off-axis refractive errors were represented in a 2-dimensional map (figure). Test-retest repeatability of this map was evaluated by repeating the measurement after an interval of time and comparing the two results.
Results:
Compared with the axial refractive error, refractive errors in the peripheral retina were frequently more hyperopic in patients with moderate to high myopia. The amount of the difference in refraction between the fovea and peripheral retina 30 degrees from the fovea reached 8 D at most and significantly correlated to the axial refractive error (R2> 0.54, P<0.02) except in the lower meridian. Overall repeatability of the map (95% limits of agreement) was +/-1.19 D, whereas that for the axial measurement was +/-0.69 D.
Conclusions:
The mapping of peripheral refractive errors demonstrated the relationship between peripheral refractive errors and ocular shape as previously reported under experimental conditions. Further studies are required to estimate systematic measurement errors involved in this method.
Keywords: refractive error development • myopia • refraction