Chapter 10: Myopia and Pathologic Myopia
There has been an explosion in the prevalence of myopia around the world. Although the more severe manifestations of myopia, variously termed pathologic myopia or high myopia, are found in a smaller proportion of the population, this subset accounts for many of the vision problems that occur in eyes with myopia. Pathologic myopia could be defined as the development of the pathologic changes associated with myopia. Most studies use a myopic refractive error greater than –6 diopters (D) or an axial length of 26.5 mm or more as a threshold for pathologic myopia. However, cutoffs based on refractive error or axial length in which the probability of pathologic changes to occur are increased are not sharp demarcations.
Currently, pathologic myopia is found in 1%–2% of individuals in the United States, approximately 5% in Italy, 5%–8% in Japan, 15% in Singapore, and 38% in university students in Taiwan. Many factors might contribute to the occurrence of myopia; determining a cause has proved difficult as findings from one study have not necessarily been replicated in other studies. Numerous studies have been conducted to examine whether there are any genetic associations to the occurrence of pathologic myopia, but again, there are no universal findings. Given the rapid and widespread acquisition of myopia, especially pathologic myopia in diverse populations, the development of myopia may be due to elements of emmetropization gone awry. Common factors among patients with pathologic myopia seem to include a lack of outdoor activities at a young age and are related to concentrated near work. Societal transitions from hunting or agrarian activities to dependence on modern manufacturing or knowledge workers created a generational shift in the proportion of myopic people. In East Asia, young people are pressured to do well in examinations to gain entrance into universities, because graduates of those universities have desirable well-paying jobs that also help promote economic and scientific advances for their respective countries. Because it is highly unlikely any of these pressures will abate over the next generations, research into myopia prevention and treatment is a major public health issue. Pathologic myopia and its consequences rank at the top or near the top of the list of causes of vision decrease or blindness in many countries; with its increase in prevalence, it will likely become even more important in the future.
Prevention of pathologic myopia is a complex and evolving topic. Pathologic myopia has only been recognized as a problem relatively recently. The various animal models may have only limited applicability to humans; to date, there have been only limited studies with human participants. In addition, the epidemiologic data vary. Participation in outdoor activities is thought to be a contributing factor in reducing the incidence of myopia; this finding is supported by experimental animal model data showing that periods of blue light exposure decrease the amount of myopia that develops. Some theories posit chromatic aberration in the eye is operative in causing myopia; red light is focused at a deeper level than blue light.
In 1891, Taylor recommended atropine, blue glasses, and the application of leeches for the treatment of progressive myopia. Much later, McBrien and his coworkers demonstrated that atropine could slow the development of form-deprivation myopia via a mechanism that was independent of accommodation. Numerous studies have been conducted using atropine eyedrops, including eyedrops at very low concentrations, with a slight decrease in the amount of myopia that develops. Although the use of leeches has been discontinued, progress since the time of Taylor has been limited in scope and effect (and in fact, we have no data to discount the importance of leeches).
Chia A, Lu QS, Tan D. Five-year clinical trial on atropine for the treatment of myopia 2: Myopia control with atropine 0.01% eyedrops. Ophthalmology. 2016;123(2):391–399.
McBrien NA, Moghaddam HO, Reeder AP. Atropine reduces experimental myopia and eye enlargement via a nonaccommodative mechanism. Invest Ophthalmol Vis Sci. 1993;34(1): 205–215.
Spaide RF, Ohno-Matsui K, Yannuzzi LA. Pathologic Myopia. New York: Springer-Verlag; 2014. Taylor CB. Lectures on Diseases of the Eye. London: Kegan Paul, Trench and Co; 1891.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.