BASICS

DESCRIPTION

Myopic degeneration is a complication of severe or progressive myopia causing mild to severe central vision loss and is one of the leading causes of visual debilitation in the world. Loss of macular function occurs secondary to macular hemorrhage, retinal pigment epithelium (RPE) atrophy, or choroidal neovascularization.

• Myopia may be divided into simple, congenital, and degenerative.

• Simple and congenital myopia are not progressive and do not develop the typical degenerative changes.

EPIDEMIOLOGY

Incidence

• The incidence of myopia varies with age but it generally occurs in the grade school years. At a young age, progressive myopia can be indistinguishable from simple or congenital myopia.

• Those with degenerative myopia often have rapidly increasing myopia and axial length through adolescence. This increase can then continue until the age of 50 years.

• The macular degenerative changes often develop in the productive years of young adulthood and continue to progress indefinitely.

Prevalence

• The prevalence of myopia in developed countries is reported to be between 11–36%. The frequency of degenerative myopia has been reported to range from 27–33% of the myopic population that corresponds to rates of 1.7–2.1% in the general population.

• The prevalence of myopia shows a marked change with age, with the peak at 20 years.

RISK FACTORS

Genetics

Simple myopia has often been described as a dominant condition but the degenerative form is thought to be autosomal recessive. However, both forms are multifactorial.

PATHOPHYSIOLOGY

• The sclera is thinned at the posterior pole with sclera ectasia and posterior staphyloma.

• The choriocapillaris is thin and there is a loss of melanocytes from the choroid.

• The RPE cells are flatter and larger before they undergo degeneration.

• Bruch’s membrane undergoes thinning, splitting, and rupturing.

ETIOLOGY

The cause of the degenerative process is not clearly understood but it may be the result of a biomechanical abnormality with progressive stretching of the sclera, leading to thinning of all layers in the posterior pole.

COMMONLY ASSOCIATED CONDITIONS

Retinopathy of prematurity and premature birth without ROP is associated with high myopia.

DIAGNOSIS

• Ophthalmic features of degenerative myopia include:

– Scleral thinning, ectasia, and posterior staphyloma

– Tilted oval disc with long vertical axis and temporal atrophy or myopic crescent

– Thinning of the pigment epithelium and choroid allowing visibility of the larger choroidal vessels giving a “tessellated fundus” appearance.

– Areas of pigment epithelial and choroidal atrophy with sharp margins sometime lined by pigment. These can progress and coalesce into larger irregular lesions with time

– Lacquer Cracks (ruptured Bruch’s elastic lamina) appear as irregular liner or stellate breaks in the pigment epithelium

– Macular hemorrhage can occur with a lacquer crack in the absence of a choroidal neovascular membrane. They can be associated with trauma

• Choroidal neovascularization.

– Hemorrhage with pigment epithelial elevation, subretinal fluid or edema

– When occurring as a dark spot in the posterior pole, it is sometimes referred to as a Foerster-Fuch’s spot.

– May occur in up to 40% of highly myopic patients. Those with patchy atrophy and lacquer cracks are at high risk.

HISTORY

Highly myopic patients with sudden vision changes and new metamorphopsia need to be evaluated for choroidal neovascularization.

DIAGNOSTIC TESTS & INTERPRETATION

Diagnostic Procedures/Other

• Flourescein angiography

• Optical coherence testing (OCT)

TREATMENT

• Address refractive error with glasses or contact lens

• Low vision support

• Choroidal neovascularization (CNV)

– Laser treatment for extrafoveal CNV but not juxtafoveal CNV due to possible long term expansion of the laser scar

– Anti-vascular endothelial growth factor (Anti-VEGF) therapy for subfoveal or juxtafoveal CNV

SURGERY/OTHER PROCEDURES

Scleral buckle or vitrectomy for retinal detachment

ONGOING CARE

FOLLOW-UP RECOMMENDATIONS

• Ophthalmologist for continued careful evaluation of both macular changes and possible peripheral retinal changes

• Low vision support and continued monitoring of refractive error. Declining vision can be due to both progressive macular changes and progression of the myopia.

PATIENT EDUCATION

Patients who are at high risk for choroidal neovascularization should be instructed to monitor detailed vision in each eye separately on a regular basis and consider using an Amsler grid.

PROGNOSIS

There is a guarded prognosis for those with progressive staphyloma. Risk of vision loss from macular atrophy or choroidal neovascularization increases with age.

COMPLICATIONS

• Visual loss from macular changes

• Retinal detachment

ADDITIONAL READING

• Rabb MF, Garoon I, LaFranco FP. Myopic macular degeneration. Int Ophthalmol Clin 1981;21:51–69.

• Hayashi K, Ohno-Matsui K, Shimada N, et al. Long-term pattern of progression of myopic maculopathy: A natural history study. Ophthalmology 2010; 117(8): 1595–1611.

• Chang LK, Spaide RF, Brue C, et al. Bevacizumab treatment for subfoveal choroidal neovascularization from causes other than age-related macular degeneration. Arch Ophthalmol 2008;126(7):941–945.

CODES

ICD9

360.21 Progressive high (degenerative) myopia

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