Etiopathogenesis and management of high-degree myopia. Part I

High-degree myopia (HM) is defined as a refractive error above -6 D (-8 diopters). An axial eyeball length above 26 mm and is also connected with excessive myopisation. Mechanical stretching and thinning of the choroids may lead to the development of irreversible degenerative changes in the eyeball and visual impairment. HM prevalence varies significantly by geographical area, ranging from 1.7-3.3%, while in highly urban regions of South-East Asia it affects up to 24% of university students. HM is not a homogenous disease. It is considered to be inherited in different patterns: dominant, autosomal recessive, and X-linked. Many genetic mutations linked to HM development have been described and the different patterns of inheritance may reflect different types of HM. Moreover, the clinical state of the HM eyeball may result from both genetic and environmental risk factors influencing the progression of the refractive error. The development and progression of HM is connected with sustained prolonged near work involving accommodation-convergence imbalance leading to retinal blur, the years spent at school, the amount of near work, especially writing and reading, which is related to slight chronic under-accommodation, and improper light stimuli in early childhood. Contemporary definitions of HM, views on etiopathogenesis, excessive axial elongation, and pathological changes within the eyeball in the course of HM leading to visual impairment are presented here. Genetic and environmental risk factors influencing the progression of HM, its significantly different prevalence in various geographical areas, and therapeutic options for the refractive error are also presented.