Light rays bounce off objects and enter the human eye through the transparent covering -- the cornea -- which bends the light through the pupil. From there, the light passes through the lens and focuses on the retina. Within the center of the retina are millions of cones and rods that convert the light into impulses and send them to the brain to produce an image. Sudden loss of vision occurs when a disorder or disease interrupts any part of this process.
Eye specialists classify vision loss as "sudden" if it develops within a few minutes to a few days. Sudden vision loss can occur in a variety of ways for various reasons. Sometimes it presents as blurred vision as a result of a loss of a portion of the field of vision. The vision loss can affect both eyes or only a single eye. Other symptoms, such as pain or swelling, may accompany a sudden loss of vision. Generally, total blindness is a result of a disorder affecting the entire eye, rather than a part of it.
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