Peripheral refraction measurement: does it matter if one turns the eye or the head?

It has been suggested that, following eye movements, the changing pressures exerted by the extraocular muscles and the lids might distort the shape of the eyeball and alter refraction across the visual field. To confirm or refute this hypothesis, the pattern of monocular peripheral refraction in the right eyes of 10 healthy young adults was measured either by turning the eye to fixate a series of horizontally spaced targets or by turning the head to view the same targets while maintaining central fixation and the eye in its primary position. In each case a fixed Shin-Nippon autorefractor was used to measure peripheral refraction at 5 degrees intervals over the central +/-30 degrees of the visual field. The duration of any eye turn was < or =1 min. Repeated-measures analysis showed no significant differences between the spherical equivalents of peripheral refraction measured under the two conditions (p = 0.223). A further study of five subjects involving 2.5-min periods of fixation with an eye or head turn of 25 degrees also showed no significant refractive differences. Thus, within the conditions of the study (eye-turn durations and field angles < or =2.5 min and 30 degrees respectively), the results fail to confirm the occurrence of large differences in peripheral refraction when measurements are made with eye turn rather than head turn.