Animal models have been pivotal in elucidating the mechanisms of myopia development and control, according to a comprehensive review undertaken by myopia expert, Mark Bullimore. By examining species ranging from chickens to monkeys to guinea pigs and mice, researchers have uncovered fundamental biological principles that mirror human refractive development – especially the process of emmetropization and the eye's response to optical defocus.
In both animals and humans, emmetropization occurs early in life and is tightly regulated by visual input. Depriving young animals of form vision using diffusers leads to axial elongation and significant myopia, closely mimicking what is seen in children with early-onset visual deprivation, such as congenital cataracts.
The “lens paradigm” (i.e. imposing hyperopic or myopic defocus through lenses to cause predictable refractive changes) has been particularly influential in refractive investigations in animal models, as well as helping to inspire human clinical interventions. For instance, peripheral hyperopic defocus induces central myopia, a finding that underpins the use of dual-focus and multifocal lenses in myopia control. These optical strategies – tested initially in primates – are now used in children to slow myopia progression.
Interestingly, changes in choroidal thickness – a key finding in animal studies – have also been observed in humans using optical coherence tomography (OCT). Though the magnitude of change is smaller in humans, short-term choroidal thickening with myopic defocus and thinning with hyperopic defocus indicate that the retina-choroid-sclera signaling cascade is conserved across species.
However, the study highlights critical caveats. For instance, many animal models are based on neonatal development stages, whereas juvenile-onset myopia in humans occurs later. Additionally, phenomena like the rebound effect after atropine cessation or the lack of efficacy of low-dose atropine in axial length control remind us that mechanisms can diverge between species.
For ophthalmologists, the translational value of animal research lies in its ability to inform optical, pharmacological, and behavioral interventions for myopia. As myopia reaches epidemic proportions globally, integrating insights from animal models with rigorous human trials will be essential for designing more effective, individualized treatment strategies.
