Retinal detachment: A separation of the retina
from its connection at the back of the eye. The separation
usually results from a tear (that is, a rent or rip, not a
tear drop) in the retina. The tear often occurs when the
vitreous gel pulls loose or separates from its attachment
to the retina, usually in the outside edges of the eye. The
vitreous is a clear gel that fills most of the inside of
the eye between the retina and the lens. If the retina is
weak when the vitreous gel pulls loose, the retina will
tear. This rip is sometimes accompanied by bleeding, or
hemorrhage, if a blood vessel is also torn.

Once the retina has torn, liquid from the vitreous gel can
then pass through the tear and accumulate behind the
retina. The build-up of fluid behind the retina is what
separates (detaches) the retina from the back of the eye.
As more of the liquid vitreous collects behind the retina,
the extent of the retinal detachment can progress and
involve the entire retina, leading to a total retinal
detachment. A retinal detachment almost always affects only
one eye. The second eye, however, must be checked
thoroughly for any signs of the problem.

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