Article

Spectacle lens compensation in the pigmented guinea pig

School of Psychology, Faculty of Science and Information Technology, The University of Newcastle, Australia.
Vision research (Impact Factor: 2.38). 12/2008; 49(2):219-27. DOI: 10.1016/j.visres.2008.10.008
Source: PubMed

ABSTRACT When a young growing eye wears a negative or positive spectacle lens, the eye compensates for the imposed defocus by accelerating or slowing its elongation rate so that the eye becomes emmetropic with the lens in place. Such spectacle lens compensation has been shown in chicks, tree-shrews, marmosets and rhesus monkeys. We have developed a model of emmetropisation using the guinea pig in order to establish a rapid and easy mammalian model. Guinea pigs were raised with a +4D, +2D, 0D (plano), -2D or -4D lens worn in front of one eye for 10 days or a +4D on one eye and a 0D on the fellow eye for 5 days or no lens on either eye (littermate controls). Refractive error and ocular distances were measured at the end of these periods. The difference in refractive error between the eyes was linearly related to the lens-power worn. A significant compensatory response to a +4D lens occurred after only 5 days and near full compensation occurred after 10 days when the effective imposed refractive error was between 0D and 8D of hyperopia. Eyes wearing plano lenses were slightly more myopic than their fellow eyes (-1.7D) but showed no difference in ocular length. Relative to the plano group, plus and minus lenses induced relative hyperopic or myopic differences between the two eyes, inhibited or accelerated their ocular growth, and expanded or decreased the relative thickness of the choroid, respectively. In individual animals, the difference between the eyes in vitreous chamber depth and choroid thickness reached +/-100 and +/-40microm, respectively, and was significantly correlated with the induced refractive differences. Although eyes responded differentially to plus and minus lenses, the plus lenses generally corrected the hyperopia present in these young animals. The effective refractive error induced by the lenses ranged between -2D of myopic defocus to +10D of hyperopic defocus with the lens in place, and compensation was highly linear between 0D and 8D of effective hyperopic defocus, beyond which the compensation was reduced. We conclude that in the guinea pig, ocular growth and refractive error are visually regulated in a bidirectional manner to plus and minus lenses, but that the eye responds in a graded manner to imposed effective hyperopic defocus.

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    • "In contrast, Schaeffel et al. (Schaeffel et al., 1988) demonstrated through the use of positive and negative lenses of specific refractive powers that chicks could accurately compensate for imposed myopic or hyperopic defocus by modulating the axial length of the eye. Lens compensation was subsequently demonstrated in tree shrews (Norton et al., 2010), monkeys (Smith et al., 2010), guinea pigs (Howlett and McFadden, 2009), and mice (Tkatchenko et al., 2010). Remarkably, studies using animal models have demonstrated that young eyes can recover from induced myopia following removal of the diffuser or negative lens (Siegwart and Norton, 1998; Wallman and Adams, 1987). "
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    ABSTRACT: Myopia is a common ocular condition, characterized by excessive elongation of the ocular globe. The prevalence of myopia continues to increase, particularly among highly educated groups, now exceeding 80% in some groups. In parallel with the increased prevalence of myopia, are increases in associated blinding ocular conditions including glaucoma, retinal detachment and macular degeneration, making myopia a significant global health concern. The elongation of the eye is closely related to the biomechanical properties of the sclera, which in turn are largely dependent on the composition of the scleral extracellular matrix. Therefore an understanding of the cellular and extracellular events involved in the regulation of scleral growth and remodeling during childhood and young adulthood will provide future avenues for the treatment of myopia and its associated ocular complications. Copyright © 2014 Elsevier Ltd. All rights reserved.
    Experimental Eye Research 04/2015; 133. DOI:10.1016/j.exer.2014.07.015
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    • "Previous studies with chickens have also reported a significant disruption of the natural diurnal rhythms in choroidal thickness in eyes exposed to myopic defocus, with choroidal rhythms found to be significantly phase advanced (Nickla et al., 1998; Nickla, 2006; Papastergiou et al., 1998). Choroidal thickening, associated with periods of myopic defocus has also been widely noted in avians (Nickla et al., 2005; Park et al., 2003; Wallman et al., 1995; Wildsoet and Wallman, 1995; Zhu et al., 2003), mammals (Howlett and McFadden, 2009), and primates (Hung et al., 2000; Troilo et al., 2000). Previous studies of daily rhythms of choroidal thickness in human eyes have only examined subfoveal measures (Brown et al., 2009; Chakraborty et al., 2011). "
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    ABSTRACT: Recent research indicates that brief periods (60 min) of monocular defocus lead to small but significant changes in human axial length. However, the effects of longer periods of defocus on the axial length of human eyes are unknown. We examined the influence of a 12 h period of monocular myopic defocus on the natural daily variations occurring in axial length and choroidal thickness of young adult emmetropes. A series of axial length and choroidal thickness measurements (collected at ∼3 hourly intervals, with the first measurement at ∼9 am and the final measurement at ∼9 pm) were obtained for 13 emmetropic young adults over three consecutive days. The natural daily rhythms (Day 1, baseline day, no defocus), the daily rhythms with monocular myopic defocus (Day 2, defocus day, +1.50 DS spectacle lens over the right eye), and the recovery from any defocus induced changes (Day 3, recovery day, no defocus) were all examined. Significant variations over the course of the day were observed in both axial length and choroidal thickness on each of the three measurement days (p < 0.0001). The magnitude and timing of the daily variations in axial length and choroidal thickness were significantly altered with the monocular myopic defocus on day 2 (p < 0.0001). Following the introduction of monocular myopic defocus, the daily peak in axial length occurred approximately 6 h later, and the peak in choroidal thickness approximately 8.5 h earlier in the day compared to days 1 and 3 (with no defocus). The mean amplitude (peak to trough) of change in axial length (0.030 ± 0.012 on day 1, 0.020 ± 0.010 on day 2 and 0.033 ± 0.012 mm on day 3) and choroidal thickness (0.030 ± 0.007 on day 1, 0.022 ± 0.006 on day 2 and 0.027 ± 0.009 mm on day 3) were also significantly different between the three days (both p < 0.05). The introduction of monocular myopic defocus disrupts the daily variations in axial length and choroidal thickness of human eyes (in terms of both amplitude and timing) that return to normal the following day after removal of the defocus.
    Experimental Eye Research 08/2012; 103:47-54. DOI:10.1016/j.exer.2012.08.002
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    • "Evidence for visually-guided emmetropization in animals has come primarily from studies in which plus or minus-power lenses have been used to affect refractive development (Schaeffel et al., 1988; Irving et al., 1992; Hung et al., 1995; Wildsoet, 1997; Smith, III and Hung, 1999; Wallman and Winawer, 2004; Shen and Sivak, 2007; Metlapally and McBrien, 2008; Troilo et al., 2009; Howlett and McFadden, 2009; Norton et al., 2010). Although generally consistent responses to plus lenses have been found in chick, the response to plus lenses in mammals has been more variable. "
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    ABSTRACT: We examined normal emmetropization and the refractive responses to binocular plus or minus lenses in young (late infantile) and juvenile tree shrews. In addition, recovery from lens-induced myopia was compared with the response to a similar amount of myopia produced with plus lenses in age-matched juvenile animals. Normal emmetropization was examined with daily noncycloplegic autorefractor measures from 11 days after natural eye-opening (days of visual experience [VE]) when the eyes were in the infantile, rapid growth phase and their refractions were substantially hyperopic, to 35 days of VE when the eyes had entered the juvenile, slower growth phase and the refractions were near emmetropia. Starting at 11 days of VE, two groups of young tree shrews wore binocular +4 D lenses (n=6) or -5 D lenses (n=5). Starting at 24 days of VE, four groups of juvenile tree shrews (n=5 each) wore binocular +3 D, +5 D, -3 D, or -5 D lenses. Non-cycloplegic measures of refractive state were made frequently while the animals wore the assigned lenses. The refractive response of the juvenile plus-lens wearing animals was compared with the refractive recovery of an age-matched group of animals (n=5) that were myopic after wearing a -5 D lens from 11 to 24 days of VE. In normal tree shrews, refractions (corrected for the small eye artifact) declined rapidly from (mean±SEM) 6.6±0.6 D of hyperopia at 11 VE to 1.4±0.2 D at 24 VE and 0.8±0.4 D at 35 VE. Plus 4 D lens treatment applied at 11 days of VE initially corrected or over-corrected the young animals' hyperopia and produced a compensatory response in most animals; the eyes became nearly emmetropic while wearing the +4 D lenses. In contrast, plus-lens treatment starting at 24 days of VE initially made the juvenile eyes myopic (over-correction) and, on average, was less effective. The response ranged from no change in refractive state (eye continued to experience myopia) to full compensation (emmetropic with the lens in place). Minus-lens wear in both the young and juvenile groups, which initially made eyes more hyperopic, consistently produced compensation to the minus lens so that eyes reached age-appropriate refractions while wearing the lenses. When the minus lenses were removed, the eyes recovered quickly to age-matched normal values. The consistent recovery response from myopia in juvenile eyes after minus-lens compensation, compared with the highly variable response to plus lens wear in age-matched juvenile animals suggests that eyes retain the ability to detect the myopic refractive state, but there is an age-related decrease in the ability of normal eyes to use myopia to slow their elongation rate below normal. If juvenile human eyes, compared with infants, have a similar difficulty in using myopia to slow axial elongation, this may contribute to myopia development, especially in eyes with a genetic pre-disposition to elongate.
    Experimental Eye Research 11/2010; 91(5):660-9. DOI:10.1016/j.exer.2010.08.010
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