Eyesight tends to disappear more gradually than suddenly. In fact, the warning signs of vision loss in adults can be so subtle that you don't even notice them until a "nuisance" complaint, like trouble focusing or irritation, sends you for an overdue eye exam. That's when an unrelated but more serious vision robber, like glaucoma, may be discovered.
"That's why a baseline exam at age 40 is important," says San Francisco ophthalmologist Andrew Iwach, a spokesman for the American Academy of Ophthalmology. "You may not have major symptoms, yet have a major problem."
Certain warning signs of vision loss, however, can be seen right under -- er, over our noses.
Warning sign: Your vision is clear one minute, fuzzy a few hours later.
Might be: Diabetic retinopathy. Fluctuating clarity -- sometimes you see fine, sometimes everything's blurry -- may mean that you have a chronic condition such as uncontrolled type 2 diabetes or uncontrolled high blood pressure that can damage the fine blood vessels of the retina, causing vision damage.
Watch for: Changes in visual clarity that happen throughout the day. Some people find it difficult to continue to do close tasks, such as reading or sewing. Pay attention to whether you have other possible signs of diabetes or high blood pressure. If you're diagnosed with one of these conditions, take special care to have regular eye exams. The odds of developing retinal damage increase the longer you have diabetes.
Warning sign: You've had a recent and inexplicable traffic accident.
Might be: Glaucoma. Admittedly, a million things can cause a fender-bender. But a loss of peripheral (side-to-side) vision is a key warning sign of glaucoma, a silent disease in which building pressure on the optic nerve begins to obscure vision because images can't be fully transmitted to the brain. Several studies have found that drivers with glaucoma have an increased risk of accidents, according to a 2011 Review of Ophthalmology report. A 2008 study paired glaucoma patients with a driving instructor and found they needed six times as many interventions from the instructor than age-matched control drivers did.
Watch for: Bumping into things or people is another indicator of losing side vision. Noticing behaviors is useful, Iwach says. The reason: "People don't usually recognize when they lose side vision because it happens slowly and the eye is designed so well that it compensates for changes until late in the disease." Because it's essentially symptomless, most glaucoma is caught during routine exams.
Warning sign: There's a frustrating dark or empty patch at the center of your vision.
Might be: Age-related macular degeneration. AMD is the leading cause of severe vision loss in people over age 50, according to the American Optometric Association. Changes to macula, part of the retina, cause this incurable sight-stealer. (A less common form, called "wet macular degeneration," can be treated with lasers.)
Watch for: Look at a straight line and it may appear wavy. Sometimes people with macular degeneration bob their heads a bit as they try to see "around" the smudgy patch. People with AMD may have trouble reading street signs, or they may give up reading or other close work, such as needlework. There may also be changes to color perception -- everything looks a little washed out.
More early warning signs of vision loss
Warning sign: Your eyelid looks funny.
Might be: Skin cancer. Not all harbingers of vision loss involve vision. Changes in the appearance of the eye itself, including the eyelid, can foretell problems. The thin, delicate tissue of the eyelid is one of the most common sites for basal cell and squamous cell carcinomas. While these types of cancer are rarely fatal, they often cause serious damage and blindness, according to the Skin Cancer Foundation.
Watch for: Eyelids that look droopy or asymmetrical, a lump or bump, persistent bleeding or irritation that doesn't go away, or a dark spot on the lid. "Any change in the appearance of the eye itself warrants getting checked out," ophthalmologist Andrew Iwach says.
Warning sign: There's a brownish tint to your vision.
Might be: Cataracts. A clouding of the lens that can affect vision in just one or both eyes, cataracts are so common that by age 80, more than half of all Americans will either have cataracts or have had surgery to correct the condition, according to the National Eye Institute.
Watch for: Generally blurred vision, as clumps of protein reduce the sharpness of the image reaching the retina. This happens so slowly that people are seldom aware of it in the early stages. As damage increases with age (usually not until the 60s but sometimes as early as the 40s), the lens takes on a brownish or yellowish tinge rather than being clear. This can cause vision to be dulled, cloudy, and slightly "dirty." Color perception can become distorted -- socks that look black to you are actually more vivid purple ones, for example. Other symptoms include being irritated by the glare of sun or lights, seeing halos around lights, and poor night vision.
Warning sign: You see a flurry of "flashes and floaters."
Might be: Impending retinal detachment. Usually a sudden event, it's considered an emergency requiring immediate care (usually surgical reattachment). But many people experience a period of increasing flashes before a retinal tear occurs.
Watch for: A greater-than-usual number of little spots and light bits seeming to float before your eyes, and with increasing frequency. Seeing some flashes and floaters is common -- they're images of particles floating in the vitreous fluid of your eye. The red flags are increased amount and frequency, as well as an increase in seeing flashes of light.
"Any difference in what's normal for you merits a call and probably an exam," Iwach says. "The older we get, the busier we get taking care of our families -- and, unfortunately, the less likely we are to take care of ourselves."