In diabetes, the retinal blood vessels can develop tiny leaks.
Blood and fluid seep from the retinal blood vessels, and fatty
material, called exudate, deposits in the retina. This causes
swelling of the retina, and it is called nonproliferative
diabetic retinopathy (NPDR). When this occurs in the central part
of the retina (the macula), vision will be reduced or blurred. Leakage
elsewhere in the retina will usually have no effect on vision.
A patient with a wet, swollen macula, or with exudate in
the macula, will experience some loss of vision, including
blurring, distortion, or darkening. If one eye is affected, the
other eye is frequently affected also, though the problem may not
be equally severe in both eyes. If the diabetic retinopathy has
affected each macula severely, central vision may be lost from
each eye. But even if the ability to see detail has been lost
from both eyes, the person with severe NPDR will usually be able
to get along fairly well by learning to use the area just outside
of the macula to see some detail. This ability to look slightly
off center usually improves with time, though the eyesight will
never be as good as it was before the macula was damaged by the
leakage of blood vessels. So patients who have NPDR will usually
be able to see well enough to take care of themselves and
continue those activities that do not require detail vision.