PATHOLOGIC MYOPIA’S IMPACT ON THE RETINA
MYOPIA IS rapidly increasing and becoming a global epidemic. In the U.S., the prevalence of myopia has doubled to 42% in the last three decades, with close to 10 million adults having high myopia (≥-6.00D), reports Ophthalmology. Also, half the world’s population will have myopia by 2050, with up to one billion having high myopia and being at increased risk of blindness if current trends continue, reports the World Health Organization.
While no definitive cause for high myopia has been discovered, research shows that genetics and environmental factors, such as near work, artificial lighting and less time spent outdoors, may play roles. High myopia is linked to pathologic myopia, which can incite progressive, irreversible vision loss and is a common cause of legal blindness in young individuals. Pathologic complications include posterior staphyloma, retinal detachment, myopic maculopathies (chorioretinal atrophy, lacquer cracks, choroidal neovascular membrane [CNVM] and Fuchs’ spot), myopic macular retinoschisis, macular hole and a dome-shaped macula.
In this column, I answer common questions about the retinal complications associated with pathologic myopia, so you can best manage these patients.
Q WHAT IS THE CLINICAL SIGNIFICANCE OF POSTERIOR STAPHYLOMA, AND WHAT IS THE BEST WAY TO DETECT IT?
A One of the hallmark findings of pathologic myopia is posterior staphyloma, which is an outpouching of scleral tissue. While staphyloma is observed in eyes that have long axial length (greater than 26.5 mm), it can also occur in eyes that have normal axial length. Also, except for inferior staphyloma in tilted disc syndrome, this defect is uniquely observed in pathologic myopia.
Staphylomas are not commonly observed in children who have pathologic myopia, but tend to develop and worsen with increasing age, according to the American Journal of Ophthalmology. This leads to increased stretching of the sclera, choroid and retina, causing various complications, such as myopic CNVM or chorioretinal atrophy.
Retinal photography and B-scan ultrasonography are good methods to detect posterior staphyloma. SD-OCT not only detects staphyloma, but it also can show how the retina and optic nerve are damaged. However, ultra-widefield imaging is the most useful technology for detecting staphyloma, especially when a wide area of the retina is involved.
Q WHAT ARE THE RISKS OF RETINAL DETACHMENT (RD) IN HIGH AND PATHOLOGIC MYOPIA PATIENTS, AND WHAT COURSE OF ACTION SHOULD BE TAKEN WITH THESE PATIENTS?
A Patients with pathological myopia are at increased risk of RD due to axial length elongation of the globe and degenerative peripheral retinal thinning (lattice degeneration). The lifetime risk of spontaneous RD in pathologic myopia is 15 to 200 times higher than in individuals who have normal retinas, reports The Lancet.
Extensive vitreous syneresis and early posterior vitreous detachment are typical in pathologic myopia. Vitreous traction can lead to full-thickness retinal tears, breaks or holes, which can lead to RD. Myopic patients with lattice lesions and symptomatic holes, tears or breaks require evaluation and treatment by a retinal specialist.
Because of the risk of RD, it is crucial for all highly myopic patients to undergo dilated retinal examinations yearly, and, you should refer them to a retinal specialist for treatment, as indicated. Also, counsel these patients to avoid dangerous activities, such as contact sports, that can potentiate the risk for a sight-threatening RD.
Q WHAT IS THE PREVALENCE OF CNVM IN PATHOLOGIC MYOPIA PATIENTS, HOW DOES IT OCCUR, AND HOW CAN ONE DETECT AND TREAT IT?
A One of the most frequent complications that cause central vision loss in pathologic myopia is CNVM. In fact, pathologic myopia is the most common cause of a macular CNVM in patients younger than age 50, according to Ophthalmology.
Myopic CNVM develop in 10% of high myopic patients, and 30% of the patients who have CNVM in one eye eventually develop CNVM in the other eye, reports the British Journal of Ophthalmology.
CNVM result from lacquer cracks, which appear as multiple yellowish-white irregular lines, usually horizontally oriented, and coursing through the posterior pole. Lacquer cracks appear as hypoautofluorescent on fundus autofluorescent imaging. Other predisposing findings for CNVM include posterior staphyloma leading to diffuse chorioretinal atrophy, which appear as yellowish-white lesions, or patchy chorioretinal atrophy, which appear as a well-defined, grayish-white lesion in the macula. These lesions represent breaks or defects in Bruch’s membrane, due to the stretching and thinning of the choroid and retinal pigment epithelial layer that occurs from pathologic myopia.
Myopic CNVM are generally Type 2 classic lesions and are smaller than those observed in AMD. On clinical examination, myopic CNVM typically appear as flat, small, grayish subretinal lesions beneath or near the fovea with or without hemorrhage. SD-OCT shows a hyper-reflective elevated lesion in the subretinal space, usually without much exudative changes, such as fluid under the neurosensory retina or intraretinal edema as compared to AMD CNVM. OCTA shows a lacy wheel pattern, or numerous tiny capillaries of active CNVM.
The principal treatment of myopic CNVM is the use of anti-VEGF drugs. After the regression, a well-defined macular atrophy, or Fuchs’ spot, gradually develops around the scarred CNVM. This is the main cause of long-term decreased vision in patients who have myopic CNVM.
Q WHAT ARE MYOPIC MACULAR RETINOSCHISIS AND DOME-SHAPE MACULA, AND HOW ARE THEY DIAGNOSED?
A Myopic macular retinoschisis is a relatively new finding in the macula in pathologic myopia patients. The diagnosis is confirmed via SD-OCT, which shows the typical splitting of neurosensory retina, bridging columns and intraretinal cysts. The condition is caused by vitreoretinal traction on the retina and can lead to other complications, such as foveal RD, lamellar or full-thickness macular hole and/or macular detachment.
Patients may complain of a focal area of blurring, metamorphopsia or scotoma that can rapidly cause decline in central vision. Vitrectomy is an option to relieve traction on the fovea and prevent complications, such as the formation of macular holes.
Another finding observed on SD-OCT in high myopic patients is a convex elevation of macula described as a dome-shaped macula. Probable pathological causes include tangential vitreomacular traction, localized choroidal or scleral thickening, hypotony and retinal resistance to scleral deformation. Additional complications include CNVM and serous RD.
ADDRESSING HIGH MYOPIA
Intervention for pathologic myopia is typically aimed at complications, such as CNVM. Highly myopic patients are also at risk for optic nerve damage or glaucoma and may become totally blind.
Let’s educate them on the importance of annual exams in detecting macular disease early, so ocular morbidity, caused by macular complications, can be reduced. OM