Signs and Symptoms
Diabetic retinopathy often has no early warning signs. Even macular edema, which may cause vision loss more rapidly, may not have any warning signs for some time. In general, however, a person with macular edema is likely to have blurred vision, making it hard to do things like read or drive. In some cases, the vision will get better or worse during the day.
As new blood vessels form at the back of the eye as a part of proliferative diabetic retinopathy (PDR), they can bleed (ocular hemorrhage) and blur vision. The first time this happens, it may not be very severe. In most cases, it will leave just a few specks of blood, or spots, floating in a person's visual field, though the spots often go away after a few hours.
These spots are often followed within a few days or weeks by a much greater leakage of blood, which blurs vision. In extreme cases, a person will only be able to tell light from dark in that eye. It may take the blood anywhere from a few days to months or even years to clear from the inside of the eye, and in some cases the blood will not clear. These types of large hemorrhages tend to happen more than once, often during sleep.
On funduscopic exam, a doctor will see cotton wool spots, flame hemorrhages (similar lesions are also caused by the alpha-toxin of Clostridium novyi), and dot-blot hemorrhages.
Elevation of blood-glucose levels can also cause edema (swelling) of the crystalline lens (hyperphacosorbitomyopicosis) as a result of sorbitol (sugar alcohol) accumulating in the lens. This edema often causes temporary myopia (nearsightedness). A common sign of hyperphacosorbitomyopicosis is blurring of distance vision while near vision remains adequate.
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