Abstract
Purpose: :
Purpose of this study is to examine the relationship between peripheral refraction and peripheral optical length for myopes and emmetropes.
Methods: :
Peripheral refraction was examined in the right eyes of 12 emmetropes and 12 myopes aged 18-30 yrs old by using an open field autorefractor (WAM-5500). Primary gaze, 5°, 10°, 15°, 20°, and 25° eccentricity on the horizontal meridian in both nasal and temporal fields were tested when viewing distance was set at 2 meters. Peripheral optical lengths at the same gazes were measured using the Zeiss IOL Master while a beam splitter was set in front of the machine to introduce a visual field channel. Spherical error, astigmatism J0 and J45 were derived from the refractive measurements and were statistically correlated to optical lengths.
Results: :
For all subjects (n=24), mean spherical error at primary gaze (-1.53±1.95D) was significantly more myopic than peripheral refractions (t=3.01, p<0.01 for the nasal; t=3.95, p<0.001 for temporal). Peripheral astigmatism was significantly increased in either nasal (t=7.70, p<0.001), but not temporally (t=16.42, p<0.001) for the J0 (0.06±0.25). Optical length in either side was significantly shorter than the central axial length (24.16±16mm) with a difference of -0.40±0.28mm (t=7.18, p<0.001) nasally and -0.61±0.32mm (t=9.64, p<0.001) temporally at 25° visual field, and the temporal relative optical length was significantly different from the nasal side (t=2.52, p<0.01). At the 25°, relative spherical error was significantly correlated to relative optical length at either the temporal side (r=0.84) or the nasal side (r=0.82), while no such significant correlation was found between the relative optical length and anyone of the relative astigmatic terms.When myopic group was separated from the emmetropic group, relative optical length was significantly shorter in myopes (-0.80±0.37mm) than in emmetropes (-0.42±0.11mm) (t=3.42, p<0.01) at the 25° temporal field. Correlation between the spherical errors and optical lengths was more prominent in myopic group (r=0.92) than in emmetropic group (r=0.27).
Conclusions: :
Peripheral spherical error, rather than astigmatism, is associated with the peripheral optical length, and the relationship is stronger in myopic eyes than in emmetropic eyes. Peripheral optical length is asymmetric to visual axis of the eye, and shorter optical length is observed in the temporal retinal side, especially in myopic eyes.
Keywords: refractive error development • myopia • astigmatism