The Effect of Temporal and Spatial Stimuli on the Refractive Status of Guinea Pigs Following Natural Emmetropization

Abstract

To understand the visual information essential for maintaining stable refraction after emmetropization, we investigated the effects of spatial and temporal stimuli on the refractive status of guinea pigs. Eighty-eight guinea pigs (4 weeks old) were randomly divided into 10 groups. Thirty animals were raised in backgrounds of gray (N = 13), square-wave (N = 9), or sine-wave grating (N = 8). Thirty-one animals were raised in gray backgrounds with three frequencies of flicker: gray-1-Hz (n = 10), gray-6-Hz (n = 12), and gray-20-Hz (n = 9). Eighteen animals were raised in regular cages with different frequencies of flicker (n = 6 respectively in 1-Hz-, 6-Hz-, and 20-Hz-flicker groups). Nine animals were raised in regular cages with no additional stimuli and used as normal controls. Ocular biometry was measured before and after 3 weeks of exposure to the test environments. Guinea pigs raised in the gray background for 3 weeks developed myopia, -6.1 ± 2.1 diopters (D), whereas those exposed to either sine-wave or square-wave gratings, or raised in regular cages, retained stable refractions. Animals in the gray-6-Hz group developed lower myopia, -2.7 ± 2.7 D, than the gray group not exposed to flicker. Animals stimulated with a range of flickering frequencies in regular cages also developed myopia but to a lower degree, -3.1 to 0.2 D, than those in gray backgrounds, -5.0 to -2.7 D. Guinea pigs require both spatial and temporal stimuli to maintain stable refractions. The influence of temporal stimuli on refraction varies with the type and amount of spatial information available in the visual environment.