Pathologic myopia is also called as high myopia or degenerative myopia, and all of them mean the same pathology.
The excessive increase of the length of eye in anterior-posterior direction (axial length) is the essential feature of pathologic myopia.
In addition to optical defocus due to excessive increase of axial length, the posterior segment of the eye is stretched and deformed, as shown by 3D MRI.
Such deformity of the posterior segments of the eye stretches, thins, and damages the neural retina and the optic nerve, which eventually develops un-corrected progressive visual loss.
Actually, pathologic myopia is a leading cause of visual impairment, and is the fourth to ninth most frequent cause of blindness worldwide. In Asian countries, pathologic myopia is the most frequent cause of visual impairment; the Tajimi Study in Japan showed that myopic macular degeneration is the leading cause of unilateral or bilateral blindness, whereas in China, it is the second most common cause of low vision/blindness in participants who were >40 years of age according to the World Health Organization.
Visual impairment in eyes with pathologic myopia is mainly due to the development of different types of myopic maculopathies. In highly myopic eyes, the axial elongation of the eye and the development of a posterior staphyloma result in a thinning of the retina and choroid, which then lead to the development of different types of myopic maculopathy. The impact of myopic maculopathy on visual impairment is important because the maculopathy is often bilateral, irreversible, and frequently affects individuals during their most productive years.8