Peripheral Refraction in Normal Infant Rhesus Monkeys

College of Optometry, University of Houston, Houston, Texas, USA.
Investigative ophthalmology & visual science (Impact Factor: 3.4). 06/2008; 49(9):3747-57. DOI: 10.1167/iovs.07-1493
Source: PubMed


To characterize peripheral refractions in infant monkeys.
Cross-sectional data for horizontal refractions were obtained from 58 normal rhesus monkeys at 3 weeks of age. Longitudinal data were obtained for both the vertical and horizontal meridians from 17 monkeys. Refractive errors were measured by retinoscopy along the pupillary axis and at eccentricities of 15 degrees , 30 degrees , and 45 degrees . Axial dimensions and corneal power were measured by ultrasonography and keratometry, respectively.
In infant monkeys, the degree of radial astigmatism increased symmetrically with eccentricity in all meridians. There were, however, initial nasal-temporal and superior-inferior asymmetries in the spherical equivalent refractive errors. Specifically, the refractions in the temporal and superior fields were similar to the central ametropia, but the refractions in the nasal and inferior fields were more myopic than the central ametropia, and the relative nasal field myopia increased with the degree of central hyperopia. With age, the degree of radial astigmatism decreased in all meridians, and the refractions became more symmetrical along both the horizontal and vertical meridians. Small degrees of relative myopia were evident in all fields.
As in adult humans, refractive error varied as a function of eccentricity in infant monkeys and the pattern of peripheral refraction varied with the central refractive error. With age, emmetropization occurred for both central and peripheral refractive errors, resulting in similar refractions across the central 45 degrees of the visual field, which may reflect the actions of vision-dependent, growth-control mechanisms operating over a wide area of the posterior globe.

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    • "Several previous observations are in agreement with the idea that the changes in ocular shape and the pattern of peripheral refractions observed during the recovery period in this experiment were visually driven. For example, emmetropization, which has been shown to be a vision-dependent phenomenon (Norton & Siegwart, 1995; Smith, 1998, 2011; Wallman & Winawer, 2004; Wildsoet, 1997), occurs in both the central and peripheral retina (Hung et al., 2008). In this respect, it is reasonable to argue that the local, regionally selective retinal mechanisms that dominate the effects of vision on refractive develop (Diether & Schaeffel, 1997; Smith et al., 2009, 2010; Wallman et al., 1987) evolved to optimize the eye's effective refractive state across the retina. "
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    ABSTRACT: This study aimed to investigate the changes in ocular shape and relative peripheral refraction during the recovery from myopia produced by form deprivation (FD) and hyperopic defocus. FD was imposed in six monkeys by securing a diffuser lens over one eye; hyperopic defocus was produced in another six monkeys by fitting one eye with -3D spectacle. When unrestricted vision was re-established, the treated eyes recovered from the vision-induced central and peripheral refractive errors. The recovery of peripheral refractive errors was associated with corresponding changes in the shape of the posterior globe. The results suggest that vision can actively regulate ocular shape and the development of central and peripheral refractions in infant primates.
    Preview · Article · Sep 2012 · Vision research
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    • "The spherical-equivalent, spectacle-plane refractive correction for each eye was measured along the pupillary axis by two experienced investigators using a streak retinoscope and averaged (Harris, 1988). We have previously shown that our retinoscopy results are strongly correlated with autorefractor measures of refractive errors in monkeys (Smith & Hung, 1999) and highly repeatable (Hung et al., 2008). The anterior radius of curvature of the cornea was measured with a hand-held keratometer (Alcon Auto-keratometer; Alcon Systems Inc, St Louis, MO) and/or a videotopographer (EyeSys 2000; EyeSys technologies Inc, Houston, TX). "
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    ABSTRACT: We analyzed the contribution of individual ocular components to vision-induced ametropias in 210 rhesus monkeys. The primary contribution to refractive-error development came from vitreous chamber depth; a minor contribution from corneal power was also detected. However, there was no systematic relationship between refractive error and anterior chamber depth or between refractive error and any crystalline lens parameter. Our results are in good agreement with previous studies in humans, suggesting that the refractive errors commonly observed in humans are created by vision-dependent mechanisms that are similar to those operating in monkeys. This concordance emphasizes the applicability of rhesus monkeys in refractive-error studies.
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    • "An initially axially-emmetropic individual with a hyperopic RPRE would have the peripheral image lying behind the retina. If the results of Hoogerheide et al. (1971) and Mutti et al. (2007) are interpreted on the basis of some of the animal experiments (Smith et al., 2005b, 2007a, 2007b, 2009; Hung et al., 2008) and the assumption is made that the state of focus in the periphery at least partly controls refractive development , this hyperopic peripheral state of focus would influence eye growth and the axial length of the eye would tend to increase until the peripheral image was in focus (Figure 3). Constraints on the way the shape of the eye could change, set by such factors as intraocular pressure, the mechanical characteristics of the sclera etc, might then mean that, in correcting the focus for the peripheral retina, growth led to a myopic fovea (Figure 3). "
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    ABSTRACT: It has been suggested that emmetropic and low-hyperopic eyes in which the refractive error in the periphery of the visual field is relatively hyperopic with respect to the axial refraction may be at greater risk of developing myopia than eyes with similar refractions but relatively myopic peripheral refractive errors. The animal and human evidence to support this hypothesis is reviewed. The most persuasive studies are those in which emmetropization has been shown to occur in infant rhesus monkeys with ablated foveas but intact peripheral fields, and the demonstration that, in similar animals, lens-induced relative peripheral hyperopia produces central axial myopia. Evidence for emmetropization in animals with severed optic nerves suggests that emmetropization is primarily controlled at the retinal level but that the higher levels of the visual system play a significant role in refining the process: there appear to be no directly equivalent human studies. Since any contribution of the higher centres to the control of refractive development must depend upon the sensitivity to defocus, the results of human studies of the changes in depth-of-focus across the field and of the contribution of the retinal periphery to the accommodation response are discussed. Although peripheral resolution is relatively insensitive to focus, this is not the case for detection. Moreover accommodation occurs to peripheral stimuli out to a field angle of at least 10 deg, and the presence of a peripheral stimulus can influence the accommodation to a central target. Although the basic hypothesis that a relatively hyperopic peripheral refractive error can drive the development of human myopia remains unproven, the available data support the possibility of an interaction between the states of focus on axis and in the periphery.
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