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Pathological Myopia

Leonardo Mastropasqua, MD and Luca Di Antonio, MD, PhD

Myopia, or nearsightedness, is a complex disease affected by both genetic and environmental factors.¹ The prevalence is lower in European, African, and Pacific Island individuals, and higher in Asian populations (about 80%), in whom it seems to be attributed to reduction of the time that children spend outdoors.¹

Pathological myopia (PM), also known as degenerative myopia, is a leading cause of irreversible visual impairment and it has rapidly increased in prevalence over the past 50 years (about 20%).¹ It refers to a condition in which individuals have an axial length > 26.5 mm corresponding to a refractive error of at least –8.0 diopter.² Beyond these values, the prevalence of myopic maculopathy has steeply increased. Although the visual impairments associated with PM can be easily managed by therapeutic interventions, there is no intervention that can prevent the development and the progression of myopia. The anatomical basis of PM has been substantially enhanced by the application of several chorioretinal imaging techniques, such as fluorescein angiography (FA), indocyanine green angiography (ICGA), optical coherence tomography (OCT), and more recently by the introduction of optical coherence tomography angiography (OCTA) into daily clinical practice.³ The reasons for the development of myopic maculopathy are not clear, but it might simply be that excessive axial elongation thins the retina and choroid, and weakens the sclera.⁴ Moreover, a recent study using high-resolution magnetic resonance imaging suggested that eyes affected by PM were not simply elongated, but also deformed and did not retain a spherical shape.⁵ Excessive axial elongation and the difference in ocular shape are related to the development of vision-threatening conditions in eyes with PM.^4,5

PM is linked to the development of pathological changes including peripapillary atrophy (Figure 26-1), patchy atrophy (Figure 26-2), dome-shaped macula (Figure 26-3), and lacquer cracks with macular hemorrhages (Figures 26-4 and 26-5). Lacquer cracks are mechanical breaks in the Bruch’s membrane/retinal pigment epithelium/choriocapillaris complex. It has been described as the association between the position of perforating scleral vessels and lacquer cracks in PM (see Figure 26-5).⁶ Lacquer cracks are a risk factor for the development of myopic choroidal neovascularization (mCNV).⁷ mCNV is the leading cause of vision loss in patients younger than 50 years, and develops in 10% of highly myopic individuals.⁷

For many years FA has served as the gold standard method for assessing the diagnosis and the treatment response of anti-vascular endothelial growth factor (anti-VEGF) drugs⁸ on the basis of late leakage observed in mCNV after dye injection.

OCTA is a newer, noninvasive tool that is able to obtain blood-flow imaging of retinal and choroidal microcirculation using the normal movement of the red blood cells into capillaries as an intrinsic contrast medium.^3,9

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