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Vision

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Clarifying the Causes of Blurry Vision

Some degree of blurred vision is a common complaint among adults of all ages. After age 50, the most frequent cause is presbyopia, an age-related refractive error (imperfection in the way the eye bends light) that can virtually always be corrected with prescription lenses. Blurred vision can also be caused by eye disorders—such as cataracts, age-related macular degeneration (AMD), and diabetic retinopathy—that become more common with age. When treatment is not possible, the visual changes sometimes caused by these disorders can often be minimized with simple lifestyle measures and special low-vision aids.

Refractive Errors

Light rays entering the eye are bent by the cornea (the outside front portion of the eye) and the lens (a flexible, transparent structure located behind the iris and the pupil). The iris is the colored part of the eye; the pupil is the dark space in the center of the iris. Normally, the rays bend so that they converge (focus) exactly on the retina (the part of the eye that sends visual signals to the brain via the optic nerve), to produce a clear image. In some people, however, the rays bend so that they focus either behind or in front of the retina, creating a blurred image.


Presbyopia is caused by age-related changes that compromise the ability of the lens to flex and change shape, a capacity known as accommodation. Impaired accommodation causes close objects to blur. People with significant presbyopia typically hold reading material at arm's length to see it clearly. The condition usually becomes noticeable around age 45, gradually progresses for about a decade, and then stabilizes.

Presbyopia can nearly always be corrected with prescription lenses: usually progressive lenses (glasses with lenses that provide clear vision for a range of distances), bifocals (glasses with lenses that correct near or distance vision), or single-vision lenses (glasses with lenses calibrated to correct near vision only). Which one you choose depends on whether any other eye problems are present. Nearsightedness (myopia), also a refractive error, is the most common coexisting problem. It usually develops earlier in life and is characterized by the inability to focus on distant objects.

The activities to be performed while glasses are worn also play a role in selecting prescription lenses. For example, a person with significant presbyopia who is very nearsighted and has a job that requires looking from nearby objects to a computer screen may prefer progressive lenses, so that the glasses can be kept on when looking from one place to another. On the other hand, that same person might prefer single-vision lenses if he is only mildly nearsighted and spends a large amount of time reading.

Contact lenses and laser surgery also are sometimes used for presbyopia. However, they do not generally provide the same degree of precision, satisfaction, and flexibility as prescription lenses. Many older adults cannot wear contact lenses because of problems like dry eye (a frequent side effect of many medications). Laser surgery has not been approved for presbyopia. Consequently, these approaches are usually best reserved for other refractive errors-especially nearsightedness.

A Cloudy Lens

Cataracts are the second most common cause of blurred vision in older people. They occur in half of those aged 65 to 74 and in 70% of people aged 75 and older. Cataract formation is a painless process characterized by the progressive clouding of the lens over many months or even years. The most common symptom is blurriness, as if the viewer were looking at the world through a cloudy piece of glass. A yellowish tinge may also appear on objects, and presbyopia may temporarily improve. Both eyes are generally affected, although one is usually worse than the other. When blurriness occurs, bright, glare-free lighting often produces a significant improvement. Fewer than 15% of cataract patients require surgery, which involves removing the damaged lens and inserting an artificial one. The causes of cataracts are largely unknown. Cigarette smoking, long-term use of corticosteroids—often prescribed for asthma or arthritis—especially at high doses, diabetes, and obesity increase risk.

Macular Degeneration

AMD is the leading reason for severe, irreversible loss of central vision in people over age 50 and may lead to blindness in a small number of cases. The disease occurs when, for reasons that are still not fully understood, the macula begins to deteriorate. The most light-sensitive portion of the retina, the macula is responsible for perceiving fine detail, which is required for central vision. There are two types:

Non-neovascular (dry). About 90% of AMD patients have this form, a slowly progressive disorder characterized by the breakdown or thinning of macular tissue. In most cases, no symptoms accompany the early stages and the condition progresses so gradually that most patients do not experience significant visual impairment. In more advanced cases, images directly in the center of the visual field, such as faces or print, may appear blurred, broken, wavy, or distorted.

Neovascular (wet). About 10% to 15% of people with dry AMD go on to develop the wet form, characterized by the growth of new, abnormal blood vessels that leak fluid under the retina. Overgrowth of connective tissue and scarring, which destroy and replace retinal tissue, may follow. Together, these changes may result in the loss of central vision. Onset may be sudden, and vision loss can be dramatic. Wet AMD is responsible for about 90% of severe AMD-related vision loss and most AMD-related blindness.

Patients with dry AMD require regular monitoring by an ophthalmologist. They should also be alert to any visual changes that occur between visits. "When reading, watch for visual distortions, like the appearance of broken or wavy lines, which could signal wet AMD," says Andrew P. Schachat, M.D., Professor of Ophthalmology and Director of the Retinal Vascular Center at Johns Hopkins Hospital. "One key technique for catching distortions is to cover one eye at a time so that each one can be checked individually. If this is not done, the good vision in one eye can mask the problem in the other." If any change is noted, consult an ophthalmologist.

Although there is no treatment for dry AMD, symptoms often improve with bright, glare-free lighting. In addition, visual aids (such as large-print books and high-power magnifiers) can help the small number of people who require them. Wet AMD can sometimes be treated with laser surgery (photodynamic therapy or photocoagulation) to seal off leaking blood vessels. When surgery is indicated, it should be scheduled as soon as possible after symptoms start.

A Complication of Diabetes

Diabetes damages blood vessels throughout the body, and blood vessels in the eye are particularly vulnerable. People with diabetes are 25 times more likely to become blind than those without the disorder, primarily owing to a diabetes-related complication called diabetic retinopathy. The disorder occurs when blood vessels in the retina leak, close, or produce new growth that leads to fluid buildup, bleeding, and scarring that can impair or destroy vision. Two types exist:

Nonproliferative retinopathy. This form occurs when leaking blood vessels cause the retina to swell, resulting in gradual blurring of images over time. In some instances, fluid builds up in the macula and seriously undermines the ability to read.

Proliferative retinopathy. In this form of the disorder, fragile new blood vessels begin to appear on the surface of the retina or the optic nerve. These new vessels can rupture and bleed in the center of the eyeball, which is normally filled with a clear fluid. As a result, blood accumulates in the central cavity, clouding vision. Severe vision loss or blindness may be the result. Scar tissue, which may lead to detachment of the retina, is also typical.

Consistent control of blood glucose and regular eye examinations performed by an ophthalmologist are two of the best ways to protect the eyes from the effects of diabetes. If retinopathy does develop, photocoagulation (sealing off leaking blood vessels by cauterization), if performed early on, can slow or stop vision loss. For patients with advanced proliferative retinopathy and extreme vision loss, a delicate surgical procedure called vitrectomy may be considered, in which scar tissue is removed and the gelatinous material that ordinarily bathes the internal structures of the eye is replaced with a saline solution.

 

From The Johns Hopkins Medical Letter: Health After 50, July 2001.

 

 

 

 


 


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2005
WHITE PAPERS
Vision

The vision White Paper from The Johns Hopkins White Papers series is an annual, in-depth report written by Hopkins physicians.


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Johns Hopkins Medical Letter: Health After 50
Keep abreast of the latest medical news with the nation's leading health newsletter for people over 50.

 

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