Myopia has been increasing rapidly throughout the developed world, suggesting environmental factors are involved.A single-author literature review in 2021 proposed that myopia is the result of corrective lenses interfering with emmetropization. Genetics
A risk for myopia may be inherited from ones parents. Genetic linkage studies have identified 18 possible loci on 15 different chromosomes that are associated with myopia, but none of these loci is part of the candidate genes that cause myopia. Instead of a simple one-gene locus controlling the onset of myopia, a complex interaction of many mutated proteins acting in concert may be the cause. Instead of myopia being caused by a defect in a structural protein, defects in the control of these structural proteins might be the actual cause of myopia. A collaboration of all myopia studies worldwide identified 16 new loci for refractive error in individuals of European ancestry, of which 8 were shared with Asians. The new loci include candidate genes with functions in neurotransmission, ion transport, retinoic acid metabolism, extracellular matrix remodeling and eye development. The carriers of the high-risk genes have a tenfold increased risk of myopia. Aberrant genetic recombination and gene splicing in the OPNLW1 and OPNMW1 genes that code for two retinal cone photopigment proteins can produce high myopia by interfering with refractive development of the eye.Human population studies suggest that contribution of genetic factors accounts for 60–90% of variance in refraction.
Induced myopia, also known as acquired myopia, results from various medications, increases in glucose levels, nuclear sclerosis, oxygen toxicity (e.g., from diving or from oxygen and hyperbaric therapy) or other anomalous conditions. Sulphonamide therapy can cause ciliary body edema, resulting in anterior displacement of the lens, pushing the eye out of focus. Elevation of blood-glucose levels can also cause edema (swelling) of the crystalline lens as a result of sorbitol accumulating in the lens. This edema often causes temporary myopia. Scleral buckles, used in the repair of retinal detachments may induce myopia by increasing the axial length of the eye. Index myopia is attributed to variation in the index of refraction of one or more of the ocular media. Cataracts may lead to index myopia. Form deprivation myopia occurs when the eyesight is deprived by limited illumination and vision range, or the eye is modified with artificial lenses or deprived of clear form vision. In lower vertebrates, this kind of myopia seems to be reversible within short periods of time. Myopia is often induced this way in various animal models to study the pathogenesis and mechanism of myopia development. Degree
The degree of myopia is described in terms of the power of the ideal correction, which is measured in diopters:
Myopia between −0.00 and −0.50 diopters is usually classified as emmetropia. Low myopia usually describes myopia between −0.50 and −3.00 diopters. Moderate myopia usually describes myopia between −3.00 and −6.00 diopters. Those with moderate amounts of myopia are more likely to have pigment dispersion syndrome or pigmentary glaucoma.