Effects of Form Deprivation on Peripheral Refractions and Ocular Shape in Infant Rhesus Monkeys (Macaca mulatta)

College of Optometry and.
Investigative ophthalmology & visual science (Impact Factor: 3.4). 06/2009; 50(9):4033-44. DOI: 10.1167/iovs.08-3162
Source: PubMed


To determine whether visual experience can alter ocular shape and peripheral refractive error pattern, the authors investigated the effects of form deprivation on refractive development in infant rhesus monkeys.
Monocular form deprivation was imposed in 10 rhesus monkeys by securing diffuser lenses in front of their treated eyes between 22 +/- 2 and 163 +/- 17 days of age. Each eye's refractive status was measured longitudinally by retinoscopy along the pupillary axis and at 15 degrees intervals along the horizontal meridian to eccentricities of 45 degrees . Control data for peripheral refraction were obtained from the nontreated fellow eyes and six untreated monkeys. Near the end of the diffuser-rearing period, the shape of the posterior globe was assessed by magnetic resonance imaging. Central axial dimensions were also determined by A-scan ultrasonography.
Form deprivation produced interocular differences in central refractive errors that varied between +2.69 and -10.31 D (treated eye-fellow eye). All seven diffuser-reared monkeys that developed at least 2.00 D of relative central axial myopia also showed relative hyperopia in the periphery that increased in magnitude with eccentricity. Alterations in peripheral refraction were highly correlated with eccentricity-dependent changes in vitreous chamber depth and the shape of the posterior globe.
Like humans with myopia, monkeys with form-deprivation myopia exhibit relative peripheral hyperopia and eyes that are less oblate and more prolate. Thus, in addition to producing central refractive errors, abnormal visual experience can alter the shape of the posterior globe and the pattern of peripheral refractive errors in infant primates.

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    • "The potential relevance of relative peripheral optical defocus and image quality on the emmetropization mechanism has been a matter of interest among scientists. Evidence suggests that hyperopic defocus in the peripheral retina is associated with myopic progression in animals [1]. In human eyes, several studies have shown that in myopes, the relative peripheral refraction tended to be hyperopic [2] [3] [4] and helped to explain the progression in myopia. "
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    • "With low-powered negative lenses, the effective strength of the defocus signal decreases with eccentricity, perhaps as a result of the normal reduction in the spatial resolving capacity of retinal neurons (i.e., the effective depth of the focus increases with eccentricity). However, ablating the central 10–12 degrees of the retina, which would alter any eccentricity-dependent variations in growth signals between the fovea and near periphery, does not appear to alter the pattern of peripheral refractions observed in monkeys with negative-lens-induced central myopia (Smith, Hung, & Huang, 2009), possibly because the effective integration zones of local retinal mechanisms are large in comparison to the size of the foveal ablations. A variety of non-visual explanations has also been put forward to potentially explain the prolate shape changes that are associated with the development of axial myopia. "
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    • "Moreover, the correlations between vitreous chamber depth and axial length in ametropic eyes were stronger than in emmetropic eyes (Table 4), i.e., the contribution of vitreous chamber depth was larger in ametropic eyes than that of emmetropic eyes, indicating that the vitreous chamber depths in the more myopic eyes were proportionally longer than those in emmetropic eyes, while those of the more hyperopic eyes were proportionally shorter. MRI imaging in monkeys with experimentally induced ametropias confirm this interpretation (Huang et al., 2009). Similar results have been reported in humans. "
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