Pathological Myopia and Posterior Staphyloma
Signs and symptoms: Physiological myopia is the most common eye disorder worldwide. A <6.00D optical aberration brought about by either increased ocular power (cornea and lens) or increased axial length is considered a normal biologic variation. Pathological myopia involves structural alterations to the globe, which may threaten sight and ocular health.
Degenerative myopia has an incidence of 2% in the United States, and is the seventh leading cause of blindness. The malady seems to have a predilection for the Chinese, Jewish, Japanese and Arab populations, and affects women twice as often as men. Blacks are virtually free of pathological myopia.
Pathological myopes may present with decreased visual acuity, an unusually large exophoria, strabismus (typically exotropia), open angle glaucoma, premature lenticular opacification and increased axial length (26.533.5mm). Dilated fundus examination may unveil any of these signs: flat, obliquely inserted discs, posterior staphyloma, a myopic crescent, patchy choroidal atrophy within the posterior pole, vitreous syneresis, breaks in Bruch's membrane with accompanying choroidal atrophy known as lacquer cracks, subretinal neovascular membrane with overlying retinal pigment epithelial hyperplasia (Fuch's spot), subretinal neovascularization without Fuch's spot (subretinal scarring, bleeding, exudate), and retinal breaks or detachments.
Patho-logical myopia has two stages, developmental and degenerative. Damage in the develo pmental stage results from axial lengthening, followed by damage from vascular alterations. Elongation of the globe, known as posterior staphyloma, occurs in stages and results from scleral thinning. This progressive scleral ectasia can form in the posterior pole (disc and macula), inferiorly, nasally or in multiple, complex patterns. Breaks in Bruch's membrane with accompany- ing choroidal atrophy create lesions known as lacquer cracks. These dehiscences are associated with increased risk for choroidal neovascularization.
Progressive myopia is associated with systemic diseases such as Marfan's syndrome, retinopathy of prematurity, Ehler's-Danlos syndrome, Stickler's syndrome and albinism.
Management: There is no treatment that regresses or arrests the progression of the staphyloma in pathological myopia. Experimentally, some have used atropine in children to ease the stresses and strains from accommodation. Others have attempted to alleviate this mechanism with bifocals. Neither modality has proved to work. Anytime you detect a posterior staphyloma, lacquer crack or Fuch's spot in the fundus, fluorescein angiography is appropriate. A- and B-scan ultrasonography can confirm the presence of increased axial length and posterior staphyloma.
Patients with pathological myopia require routine monitoring for choroidal neovascularization membrane (CNVM) formation. Angiographically definable extrafoveal or juxtafoveal subretinal neovascular membranes may warrant treatment with argon laser photocoagulation. However, due to the globe elongation and tissue stretching in this condition, the laser scars will likewise stretch and enlarge, and may adversely impact vision.
Some clinicians have used photodynamic therapy (PDT) off-label in degenerative myopia for patients with juxtafoveal and extrafoveal membranes. PDT and macular translocation may be options for subfoveal CNVM in pathological myopia. You must also monitor patients for retinal detachment. Patients with pathological myopia should receive at least annual dilated fundus examinations.
Both spectacles and contact lenses can be effective in treating the refractive error. Counsel patients with high myopia to choose zyl frames to mask the increased edge thickness of lenses. High-index glass and plastic, and polycarbonate lenses are also suitable for these prescriptions (with the last also providing a greater degree of protection). Special edge polishing and buffing can also improve lens cosmetics.
Both soft and gas-permeable contact lens designs are plausible. While soft lenses offer increased comfort and convenience, you need to monitor patients closely for hypoxia. Gas-permeable lenses offer solid optics and excellent physiology. In cases of high myopia, it may be necessary to specify a minus-edge lenticular design to minimize the complications and discomfort of a thickened skirt. LASIK is not a reasonable solution for patients with pathological myopia. Intraocular lens implantation may be a viable refractive surgery alternative.
Because pathological myopia results from stretching of the globe, it compromises ocular stability and strength. Counsel patients to avoid dangerous circumstances and activities. Contact sports or activities that jolt the body increase the risk for retinal detachment.
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