老年性黄斑变性_临床常见疾病医学英语文献翻译_免费在线阅读收听下载

What is age-related macular degeneration?
Age-related macular degeneration is the leading cause of permanent blindness in the elderly. It is a bilateral disease, the average age of visual loss in the first eye being 65 years, with about a 12% incidence of involvement of the second eye each year.
About 60% of patients are therefore legally blind in both eyes by the time they reach their seventieth birthday.
What causes age-related macular degeneration?
The exact cause is unknown, but the incidence increases with each decade over age
50. Other associations besides age include race (usually Caucasian), sex (slight female predominance), family history, and a history of cigarette. The disease includes a broad spectrum of clinical and pathologic findings that can be classified into two groups: nonexudative ("dry") and exudative ("wet"). Although both types are progressive and usually bilateral, they differ in their manifestations, prognosis, and management.
The more severe exudative form accounts for approximately 90% of all cases of legal blindness due to age-related macular degeneration.
What are symptoms of age-related macular degeneration?
Nonexudative Macular Degeneration
Nonexudative age-related macular degeneration is characterized by variable degrees of atrophy and degeneration of the outer retina. retinal pigment epithelium, Bruch's membrane and choriocapillaris. Of the ophthalmoscopically visible changes in the retinal pigment epithelium and Bruch's membrane, drusen are the most typical. Drusen are discrete, round, yellow-white deposits of variable size beneath the pigment epithelium and are scattered throughout the macula and posterior pole. With time, they may enlarge, coalesce, calcify and increase in number. In addition to drusen, clumps of pigment irregularly dispersed within depigmented areas of atrophy may progressively appear throughout the macula. The level of associated visual impairment is variable and may be minimal.

Exudative Macular Degeneration
Although patients with age-related macular degeneration usually manifest nonexudative changes only, the majority of patients who experience severe vision loss from this disease do so from the development of subretinal neovascularization and related exudative maculopathy. Serous fluid from the underlying choroid can leak through small defects in Bruch's membrane, causing focal detachment of the pigment epithelium. Additional fluid may lead to further separation of the overlying sensory retina, and vision usually decreases if the fovea is involved. Retinal pigment epithelial detachments may spontaneously flatten, with variable visual results, and leave a geographic area of depigmentation at the involved site.
In growth of new vessels from the choroid into the subretinal space is the most important change that predisposes patients with drusen to macular detachment and irreversible loss of central vision. These new vessels grow in a flat cartwheel or sea-fan configuration away from their site of entry into the subretinal space.
Although some subretinal neovascular membranes (SRNVMs) may spontaneously regress, the natural course of subretinal neovascularization in age-related macular degeneration is toward irreversible loss of central vision over a variable period of time. The sensory retina may be damaged by long-standing edema, detachment, or underlying hemorrhage. Furthermore, a hemorrhagic detachment of the retina may undergo fibrous metaplasia, resulting in an elevated subretinal mass called a disciform scar. This elevated fibrovascular mound of variable size represents the cicatricial end stage of exudative age-related macular degeneration. It is usually centrally located and results in permanent loss of central vision.
How is age-related macular degeneration diagnosed?
• Clinical features
Nonexudative Macular Degeneration
It is by far the most common type of AMD. It typically causes a gradual mild to moderate impairment of vision over several months or years. This type of AMD is either due to a slow and progressive atrophy of the RPE and photoreceptors or follows collapse of an RPE detachment. Clinically, dry AMD is characterized by sharply circumscribed circular areas of atrophy of the RPE associated with varying degrees of loss of the choriocapillaris. During the late stages the larger choroidal vessels become prominent within the atrophic areas and pre-existing drusen disappear.
Exudative Macular Degeneration
This type is also sometimes referred to as 'neovascular' AMD. Although it is less common than the non-exudative type, its effects on vision are frequently devastating.

In contrast to patients with non-exudative AMD in whom visual impairment is gradual, those with exudative type may lose all central vision within a few days. Exudative AMD may occur in isolation or in association with non-exudative AMD. Two important features of exudative AMD are detachment of the RPE and choroidal neovascularization.
• Fluorescein angiography
RPE 'window' defect: The associated atrophy of the RPE (Retinal Pigment Epithelium) overlying drusen gives rise to increased background choroidal fluorescence, which appears early in the angiogram as multiple hyperfluorescent spots. FA may also reveal lesions that are not apparent ophthalmoscopically.
Staining: Drusen may retain fluorescein dye for abnormally long periods of time after most of it has emptied. The actual dimensions of the hyperfluorescent areas seen 20 minutes after dye injection are the same as during the early stages of dye transit.
This phenomenon indicates that fluorescein molecules have not leaked but have merely adhered to the lesions.
Leak: The new vessels within the subretinal neovascular membranes (SRNVMs) fill in a 'lacy' pattern during the very early phase of dye transit, fluoresce brightly during peak eye transit (20-30 seconds after injection), and then leak with 1-2 minutes. The fibrous tissue within the membrane then stains with dye and leads to late hyperfluorescence. In eyes with associated detachments of the RPE, the SRNVM fluoresces brighter than the detachment and appears to leak as the angiogram progress.
How is it treated?
Nonexudative Macular Degeneration
There is no generally accepted means of preventing of this type of macular degeneration. A combination of oral antioxidants and zinc is modestly effective in preventing progression of macular drusen to advanced macular degeneration. Laser retinal photocoagulation may have a beneficial effect on drusen but has not yet been shown to improve visual outcome. Most patients with macular drusen never experience significant loss of central vision; the atrophic changes may stabilize or progress slowly.
However, the exudative stage may develop suddenly at any time, and in addition to regular ophthalmic examinations, patients are given an Amsler grid to help monitor and report any symptomatic changes.
Exudative Macular Degeneration
In the absence of subretinal neovascularization, no medical or surgical treatment of serous retinal pigment epithelial detachment is of proved benefit. If a well-defined extrafoveal (≥200m from the center of the foveal avascular zone) subretinal neovascular membrane is present laser photocoagulation is indicated. Angiography defines the precise location and borders of the neovascular membrane, which is then completely ablated by heavy confluent laser burns. Photocoagulation destroys the overlying retina as well but is worthwhile if the subretinal membrane can be halted short of the fovea.
Krypton laser photocoagulation of juxtafoveal (<200um from the center of the foveal avascular zone) subretinal neovascularization is recommended in nonhypertensive patients. In eyes with predominantly classic subfoveal neovascularization, the use of intravenous verteporfin and photodynamic therapy is beneficial. At this time the effectiveness of parenteral interferon, retinal radiation, or submacular surgery has not been proved. The potential benefit of other modalities, including antiangiogenesis agents and transpupillary thermotherapy, is currently under study.

老年性黄斑变性

老年性黄斑变性

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