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Pathologic Myopia ((FULL))

Pathologic myopia represents a subgroup of myopia and affects up to 3%of the world population.[2] Vision lossrelated to pathologic myopia is of great clinical significance as it can beprogressive, irreversible and affects individuals during their most productiveyears. High myopia is defined asrefractive error of at least -6.00D or an axial length of 26.5mmor more[2]. The definition of pathologic myopia in early studies has been inconsistent and mostly revolved around a combination of refractive error and axial length, which may simply reflect a high degree of myopia. Additionally, there was no clear evidence for the cutoff values chosen. In recent years, the definition of pathologic myopia has shifted to "the presence of myopic maculopathy equal to or more severe than diffuse chorioretinal atrophy."[3] Myopic maculopathy includes diffuse chorioretinal atrophy, patchy chorioretinal atrophy, lacquer cracks, myopic choroidal neovascularization (myopic CNV), and CNV-related macular atrophy.

Pathologic Myopia

Theoverall global prevalence is estimated to be 0.2-3.8% with regional variability, but varying definitions of pathologic myopia used in early epidemiological studies may limit the comparability of findings.[4] The prevalence ofpathologic myopia-related visual impairment has been reported as 0.1%-0.5% inEuropean studies and 0.2% to 1.4% in Asian studies.[5]

The main factors proposed for driving the development of pathologic myopia are elongation of the axial length and posterior staphyloma.[6] Biomechanical forces related to axial elongation of the eye result in stretching of the ocular layers and progressive thinning of the retina, choroid and sclera.[2]

Both environmental and genetic factors play a role in the development of myopia, which is further discussed in the corresponding article. Currently, the roles of known myopia-associated genetic variants have not been well established in the development of pathologic myopia.[7] Primary risk factors for pathologic myopia include older age, greater axial length, and higher myopic spherical equivalent.[4] Additional possiblerisk factors such as female gender, larger optic disc area and family historyof myopia have been suggested.[2][8][5] The role of education level in the development of pathologic myopia is currently unclear.[4][9]

Assessment of visual acuity, intraocular pressure, pupillaryreaction and dilated fundus exam are essential. A thorough macular examination and peripheral depressed examination are key to detecting complications related to pathologic myopia. In particular, lacquer cracks, myopic schisis, or choroidal neovascularization in the macular area and holes or tears in the periphery of the retina. Assessment of visual fields and Amsler grid testing may be beneficial.

Progressive retinal pigment epithelial (RPE) thinning andattenuation develops in various clinical stages throughout the fundus. A tessellated appearance corresponding toirregular distribution of RPE atrophy and variable light reflection may beappreciated even in young patients with high myopia. When RPE attenuation surrounds the opticdisc, this hypo-pigmented finding is described as peri-papillary atrophy.

Fuchs spots (also referred to as Forster-Fuchs spots) is an area of RPE hyperplasia suspected to be the response of the RPE to previous regressed CNV. Myopic CNV is the most common cause of vision loss in high myopia and has been reported in 5% to 10% of cases of pathologic myopia.[10][11]

Staphyloma development, characterized by outpouching of scleral tissue typically involving the optic disc or macula, is a common occurrence, estimated in 35% of eyes with high myopia.[12] This can be difficult to appreciate with bio-microscopy but is evident on Optical Coherence Tomography (OCT) or B scan ophthalmologic ultrasound. Staphylomata are commonly associated with lacquer cracks, RPE attenuation, epiretinal membrane and macular or foveal schisis.

Given the lack of a centralized definition and terminology for pathologic myopia, an international group of experts in high myopia developed a simplified, systematic classification based on a meta-analysis of pathologic myopia (META-PM).[13] Myopic maculopathy was classified into five different categories based on atrophic change.

Recently, it has been noted that many patients with macular changes from pathologic myopia are not sufficiently represented by an atrophy-centered classification system. A newly proposed ATN classification system for myopic maculopathy includes atrophic (A), tractional (T) and neovascular (N) components.[6]

Fluorescein Angiography is useful for evaluating myopic patients for development of CNV. Early images may show transmission defects in patches or areas of RPE atrophy in the macula and/or around the optic disc. Angiography can identify lacquer cracks in early and transit phases by linear distribution of transmission defect. In pathologic myopia, the development of CNV tends to be smaller and less exudative compared to CNV seen in AMD. Myopic CNV may appear as a focus of hyperfluourescence with a rim of hypoflourescence corresponding to hyperpigmentation at the border of the lesion. Any associated hemorrhage will result in blocked fluorescence. Leakage is seen in late images with or without blurring of the pigmented rim. The leakage present with myopic CNV is more subtle than with CNV related to AMD, and it is common that the CNV leakage may be partially or completely obscured by overlying subretinal hemorrhage.

Indocyanine green angiography (ICG) may be more sensitive for detecting CNV as the vascular leakage in pathologic myopia is typically less prominentthan for AMD-related pathology and can be more easily missed on fluorescein angiography. Despitesubtler findings on imaging studies with myopic CNV compared to those with AMD-related CNV, patients often note that these smaller lesions alter the visual perception significantly.

Recently, swept source and ultra-widefield (UWF) OCT have been implemented to evaluate various tissues affected by pathologic myopia. Swept-source OCT uses a wavelength-sweeping laser as the light source and has less sensitivity roll-off with tissue depth than conventional spectral-domain OCT. Using a longer central wavelength, penetration into deeper tissues and enhanced evaluation of the choroid and sclera are potentially possible. UWF-OCT is similar to swept source OCT but uses multiple scan lines to generate scan maps, which has been utilized to visualize posterior staphylomas, myopic macular retinoschisis, and dome-shaped macula. The data provided by these newer imaging techniques may help in understanding the pathophysiology of pathologic myopia as well as new therapeutic approaches.[18]

Patients with stable high myopia may be followed annually forvisual acuity, refraction and general ophthalmic health. In the case of development of CNV or othercomplications, patients are followed more closely as determined by their treatmentregimen.

There is no topical, local or systemic pharmacotherapy or surgery that is known to alter effectively the increase in axial length and thinning that occurs in the sclera, choroid, and retina of eyes with pathologic myopia. Animal and in-vitro studies have shown some promise in scleral collagen crosslinking to arrest the progression of pathologic myopia but further research is needed to elucidate these effects.[19] There are, however, treatments available for CNV, a major complication of pathologic myopia.

The first widely adopted therapy for CNV in pathologic myopia wasphotothermal laser ablation of the new vessels. This treatment was complicated by a high rate of recurrence and thetendency of the photocoagulation scars to expand over time, increasing the risk of central vision loss as the border of the laser scar encroached or expanded into the fovea.[8]

Complications associated with visual morbidity in pathologic myopia include progressive thinning and atrophy resulting in photoreceptor loss, development of CNV, macular hole, pigment epithelial detachments and macular or foveal detachments. Ninety-percent of patients with CNV are expected to have atrophy surrounding any previously regressed CNV.[2] Peripheral retinal detachment is another complication.

Progressive visual decline in the form of progressive chorioretinal thinning, atrophy and stretching of existing scars is expected in about 40% of patients with pathologic myopia. [2] In one study over a 6-year period, 1.2% of myopic eyes developed pathologic myopia and 17% with existing pathologic myopia experienced progression. Baseline myopia severity and axial length were strong predictors of worsening prognosis, and these factors were associated with poorer visual acuity and vision-related quality of life.[23]

In a report from the Rotterdam Study published in 1998, pathologic myopia was the third leading (6%) cause of blindness and also the third leading (6%) cause of low vision in subjects aged 55 years or older (3).

In a report from the Beijing Eye Study published in 2006, degenerative myopia was responsible for the second leading (32.7%) cause of low vision and also the second leading (7.7%) cause of blindness. Cataract was the most frequent cause of both low vision and blindness. Myopia was the most frequent cause of both low vision and blindness in a population aged 40-49 years (5).

In the United States, the prevalence of myopia was 24% in the population aged 40 years and older (i.e., 34 million people), but it varied depending on ethnicity. The highest prevalence was for Caucasians (26%), and lower for Hispanics (18%), and African-Americans (15%). Moreover, myopia prevalence is predicted to increase by 2050 such that there will likely be 45 million people aged 40 years and older affected (6).

Myopic traction maculopathy is characterized by retinal thickening, retinoschisis, lamellar macular hole formation and foveal detachment associated with high myopia (Figure 8). Recently, ultra-widefield-SS-OCT revealed that MTM is present within the area of the staphylomas, and paravascular vitreal adhesions could play an important role in the development of MTM.28,29 During its natural course, MTM could progress to a full-thickness macular hole and macular hole retinal detachment, owing to collective retinal traction from the adherent vitreous cortex, epiretinal membrane, internal limiting membrane, retinal vessels and posterior staphyloma.30 Therefore, release of the retinal traction by pars plana vitrectomy with internal limiting peeling effectively resolves MTM and prevents macular hole and macular hole retinal detachment. However, postoperative macular hole opening could occur in 5 to 20 percent of the eyes following vitrectomy with ILM peeling, owing to the extremely thin fovea in MTM. The fovea-sparing ILM peeling technique is effective in preventing macular hole development.31 041b061a72


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