Animal models in myopia research

Abstract

Our current understanding of the development of refractive errors, in particular myopia, would be substantially limited had Wiesel and Raviola not discovered by accident that monkeys develop axial myopia as a result of deprivation of form vision. Similarly, if Josh Wallman and colleagues had not found that simple plastic goggles attached to the chicken eye generate large amounts of myopia, the chicken model would perhaps not have become such an important animal model. Contrary to previous assumptions about the mechanisms of myopia, these animal models suggested that eye growth is visually controlled locally by the retina, that an afferent connection to the brain is not essential and that emmetropisation uses more sophisticated cues than just the magnitude of retinal blur. While animal models have shown that the retina can determine the sign of defocus, the underlying mechanism is still not entirely clear. Animal models have also provided knowledge about the biochemical nature of the signal cascade converting the output of retinal image processing to changes in choroidal thickness and scleral growth; however, a critical question was, and still is, can the results from animal models be applied to myopia in children? While the basic findings from chickens appear applicable to monkeys, some fundamental questions remain. If eye growth is guided by visual feedback, why is myopic development not self-limiting? Why does undercorrection not arrest myopic progression even though positive lenses induce myopic defocus, which leads to the development of hyperopia in emmetropic animals? Why do some spectacle or contact lens designs reduce myopic progression and others not? It appears that some major differences exist between animals reared with imposed defocus and children treated with various optical corrections, although without the basic knowledge obtained from animal models, we would be lost in an abundance of untestable hypotheses concerning human myopia.

Three-dimensional OCT based guinea pig eye model: relating morphology and optics

“…The use of animal models in myopia research (such as chickens, primates, tree shrews, guinea pigs or mice) allows testing the impact of manipulated visual experience on emmetropization and determination of the underlying mechanisms, as well as the effect of interventions [3]. Additionally, longitudinal studies of myopia development can occur within a much shorter time period than in humans.…”

Myopia-Inhibiting Concentrations of Muscarinic Receptor Antagonists Block Activation of Alpha2A-Adrenoceptors In Vitro

“…Diffusers [32][33][34] and negative lenses 35,36 induce large changes in axial length and refractive error (À5 to À15 diopter [D]) in a matter of days, and results from chick experiments can usually be replicated in mammals and nonhuman primates. 37 Interpretations of results, using mAChR antagonists to prevent FDM in the chick, have generally presumed that these ligands work the same way at avian receptors as they do at human or other mammalian receptors. That said, the chick retinal structure and G-protein receptor sequences differ significantly from those of mammals.…”

The chick eye in vision research: An excellent model for the study of ocular disease

“…Total natural accommodation in chickens is 15–17 D, as measured by Schaeffel and Howland (1987) using infrared photoretinoscopy and photokeratometry. Accommodation in chicks is estimated to occur at a rate of 80 D/s (Schaeffel and Feldkaemper, 2015), much faster than corresponding human estimates of 10 D/s (Schaeffel et al, 1993). The mechanism of accommodation in the chick has been debated.…”