Experimental models of myopia development: A review of literature

Myopia is one of the most prevalent refractive errors and one of the leading causes of visual impairment and blindness worldwide. It results from a mismatch between the axial length and optical power of the eye, resulting in a focal plane that lies in front of the retina. In children and young adults, myopia is most commonly caused by excessive elongation of the eyeball during development - a hallmark of school-age and some early-onset genetic forms of myopia. However, myopic refractive error can also result from other mechanisms, such as increased lens power in age-related nuclear cataracts or corneal steepening in keratoconus, which are not associated with axial elongation. The prevalence of myopia in young Asian adults has increased from 20-30% to 80-85% over the last 50 years. In contrast, recent meta-analytic data for European young adults, emphasizing studies with cycloplegic refraction essential for accuracy, indicate myopia prevalence rates of approximately 19-24%. The prevalence of high myopia (greater than or equal to-6.0 diopters) has increased disproportionately to myopia in the last 50 years, from 1-5% to 10-20% and became a global problem. The reason for this state of affairs is believed to be lifestyle and prolonged near vision activities. Although refractive error can be corrected, sight-threatening pathologies such as retinal detachment, macular degeneration, glaucoma, and cataracts are more challenging to control. Owing to years of research, the biological mechanisms of eye growth and refractive development are increasingly elucidated. The signaling cascade mechanisms that link the retinal image processing and alterations in choroidal thickness and scleral development have also been studied. While the retina can detect defocus and changes in defocus, decades of research have led to a growing understanding of the fundamental pathways in visually guided eye growth, yet the precise initial mechanisms by which the retina senses and transduces these optical signals continue to be an active and important area of investigation. Animal studies have demonstrated that the retina can locally regulate visually guided eye growth through intrinsic mechanisms, even in the absence of direct input from the brain. The precise molecular mechanisms underlying common forms of myopia, particularly those involving axial elongation, are yet to be fully elucidated. This reflects the complexity and multifactorial influences inherent even in these prevalent forms, alongside the challenges posed by experimental models in completely recapitulating all aspects of the human condition.