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The relationship between myopia, spatial frequency deprivation and luminance in the Guinea pig eye

McFadden, S.A., Metse, A.ORCID: 0000-0002-8641-1024 and Bowrey, H.E. (2012) The relationship between myopia, spatial frequency deprivation and luminance in the Guinea pig eye. Investigative Ophthalmology and Visual Science, 53 . Art. 3464.

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Abstract

Purpose: : Myopia is a refractive error caused when the eye grows too rapidly so that images are short focussed in front of the retina. Primates, mammals, birds and fish all develop myopia if the eye is deprived of form vision using a translucent diffuser. These diffusers allow light but at a reduced luminance. We studied the effect of different degrees of spatial frequency deprivation on ocular growth in a mammalian eye and compared the changes to that induced by reductions in luminance alone.

Methods: : Guinea pigs were assigned to one of 8 groups (n=52) and wore a filter on one eye from 6-13 days of age. The 8 filters were: a standard diffuser (optical density of 0.6); or one of five Bangerter Occlusion foils (BF: 0.8, 0.6, 0.4, 0.2, Light perception only, Fresnel Prism and Lens Co.) which differed in their cut-off spatial frequencies (reported acuities visible through each foil of 20/25, 20/30, 20/50, 20/100 and 0 respectively), or one of two Kodak Wratten neutral density filters (ND, Edmund Optics, optical density grades 0.1 and 0.6). The two ND filters were matched to the minimum and maximum luminance decrement caused by the other filters. Refractive error and ocular elongation measured with high frequency ultrasound were ascertained after 7 days of filter-wear.

Results: : We found that the degree of myopia was proportional to the spatial frequency cut-off (difference between the eyes ranged between -6.1D to -0.2D) due to a gradual elongation of the vitreous chamber and thickening of the crystalline lens. A corresponding reduction in luminance from the ND filters failed to cause a proportional increase in eye growth and had the same effect as wearing a plano lens. The ND filters caused significantly less myopia than the equivalent BF (OD 0.6: -1.8D Vs. -6.1D, p < 0.001; OD 0.1: -1.9D Vs. -3.9D, p < 0.001 for ND Vs. BF respectively). The acuity of the guinea pig eye is ~6 c/d, yet surprisingly, deprivation of the eye to even higher spatial frequencies (up to 12 c/d) caused myopia (60% of maximum).

Conclusions: : Excessive ocular growth and myopia can be induced with any spatial frequency reduction within the visual acuity range and possibly beyond; while chronic luminance reduction alone has little influence on mammalian ocular growth.

Item Type: Journal Article
Publisher: Association for Research in Vision and Ophthalmology
Copyright: © 2012, The Association for Research in Vision and Ophthalmology, Inc.
URI: http://researchrepository.murdoch.edu.au/id/eprint/58159
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