What do we know about human myopia?
Although biometric studies are available to provide good evidence that myopia is mainly axial in origin, there are many missing links in our knowledge. Although myopes are over-represented in glaucoma statistics, data are equivocal in terms of whether myopia is causally linked to increased IOP, and much is left to be learnt about the scleral changes underlying ocular enlargement in human myopia. More recently, attention has been focused on ocular optical aberrations as a possible cause of retinal image degradation leading to myopia. However, while increased aberrations have been linked to myopia, here also the data are equivocal and causality not established. Nonetheless, this is another hot topic. That bifocal corrections trialed as a treatment for myopia, appear to be somewhat successful in those exhibiting esophoria (overconvergence) at close distances, supports the notion that defocus may underlie myopia progression for this subgroup of myopes. Finally, the possibility that there are diurnal rhythms in humans, like those identified in the chick and marmoset for growth and intraocular pressure, and the further possibility that they might be altered in myopic eyes is only now being explored.
Abnormal vision and refractive development
Experimental paradigms for studying myopia make use optical and/or neurotoxic manipulations to alter eye growth and thus refractive development. Ocular pathologies that preclude normal vision in early life are likely to and, in most cases, do interfere with emmetropization. As already indicated, form deprivation in animal studies has analogies in conditions that affect the ocular media such as cataracts and ptosis that have been linked to increased ocular growth. In addition, conditions that affect the retina, for example albinism, also perturb emmetropization. Potentially of interest here is that specific conditions appear to have characteristic refractive patterns. Understanding these conditions better through more thorough documentation of their developmental profiles has the potential to provide new insights into the emmetropization process.
Although biometric studies are available to provide good evidence that myopia is mainly axial in origin, there are many missing links in our knowledge. Although myopes are over-represented in glaucoma statistics, data are equivocal in terms of whether myopia is causally linked to increased IOP, and much is left to be learnt about the scleral changes underlying ocular enlargement in human myopia. More recently, attention has been focused on ocular optical aberrations as a possible cause of retinal image degradation leading to myopia. However, while increased aberrations have been linked to myopia, here also the data are equivocal and causality not established. Nonetheless, this is another hot topic. That bifocal corrections trialed as a treatment for myopia, appear to be somewhat successful in those exhibiting esophoria (overconvergence) at close distances, supports the notion that defocus may underlie myopia progression for this subgroup of myopes. Finally, the possibility that there are diurnal rhythms in humans, like those identified in the chick and marmoset for growth and intraocular pressure, and the further possibility that they might be altered in myopic eyes is only now being explored.
Abnormal vision and refractive development
Experimental paradigms for studying myopia make use optical and/or neurotoxic manipulations to alter eye growth and thus refractive development. Ocular pathologies that preclude normal vision in early life are likely to and, in most cases, do interfere with emmetropization. As already indicated, form deprivation in animal studies has analogies in conditions that affect the ocular media such as cataracts and ptosis that have been linked to increased ocular growth. In addition, conditions that affect the retina, for example albinism, also perturb emmetropization. Potentially of interest here is that specific conditions appear to have characteristic refractive patterns. Understanding these conditions better through more thorough documentation of their developmental profiles has the potential to provide new insights into the emmetropization process.
