High myopia usually describes myopia of −6.00 or more. People with high myopia are more likely to have retinal detachments and primary open angle glaucoma. They are also more likely to experience floaters, shadow-like shapes which appear in the field of vision. In addition to this, high myopia is linked to macular degeneration, cataracts, and significant visual impairment. Age at onset
Myopia is sometimes classified by the age at onset:
Congenital myopia, also known as infantile myopia, is present at birth and persists through infancy. Youth onset myopia occurs in early childhood or teenage, and the ocular power can keep varying until the age of 21, before which any form of corrective surgery is usually not recommended by ophthalmic specialists around the world. School myopia appears during childhood, particularly the school-age years. This form of myopia is attributed to the use of the eyes for close work during the school years. A 2004-2015 Singapore-Sydney study of children of Chinese descent found that time spent on outdoor activities was a factor. Adult onset myopiaEarly adult onset myopia occurs between ages 20 and 40. Late adult onset myopia occurs after age 40. Prevention
Various methods have been employed in an attempt to decrease the progression of myopia, although studies show mixed results. Many myopia treatment studies have a number of design drawbacks: small numbers, lack of adequate control group, and failure to mask examiners from knowledge of treatments used.
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.