Macular degeneration

Macular degeneration, which is atrophy or degeneration of the macular disk, accounts for about 12% of all cases of blindness in the United States and for about 17% of new cases of blindness. It’s one of the causes of severe irreversible loss of central vision in people older than age 50. It affects slightly more women than men.

Types of Macular Degenaration
Two types of age-related macular degeneration occur. 

The dry, or atrophic, form is characterized by atrophic pigment epithelial changes and is usually associated with a slow, progressive distortion of straight lines or edges and central visual loss. 

The wet, or exudative, form causes rapid onset of visual impairment. It’s characterized by subretinal neovascularization that causes leakage, hemorrhage, and fibrovascular scar formation, which produce significant loss of central vision.

Pathophysiology

Age-related macular degeneration results from the formation of drusen (clumps of epithelium) or subretinal neovascular membrane in the macular region. It may be hereditary. Cigarette smoking and lack of antioxidants, such as vitamins C and E, may also enhance occurrence.

Underlying pathologic changes occur primarily at the level of the retinal pigment epithelium, Bruch’s membrane, and choriocapillaris in the macular region. Drusen (bumps), which are common in elderly people, appear as yellow deposits beneath the pigment epithelium and may be prominent in the macula.

Signs and symptoms
The patient notices a change in central vision; for example, he may notice a blank spot in the center of the page when reading.

Diagnosis
The following tests are used to diagnose macular degeneration:

• Indirect ophthalmoscopy: may reveal gross macular changes
• I.V. fluorescein angiography: may show leaking vessels as fluorescein dye flows into the tissues from the subretinal neovascular net.

Treatment
Laser photocoagulation reduces the incidence of severe visual loss in patients with subretinal neovascularization. Photodynamic therapy with vertepor-fin, a newer form of laser therapy, is effective in selected patients.