Webster's New World Medical Dictionary

lights, flashing
A sensation that is created when
the clear, jelly-like substance that fills the middle of
the eye (vitreous humor) shrinks and tugs on the
retina. These flashes of light can appear off and on
for several weeks or months. As a person ages,
flashes are likely to occur increasingly often.
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lights, flashing
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Flashes usually do not reflect a serious problem.
However, if flashing lights suddenly appear or
increase, an ophthalmologist should be consulted
immediately, to see whether the retina has been
torn. Flashes of light that appear as jagged lines or
“heat waves” in both eyes, often lasting 10 to 20
minutes, are frequently caused by migraine, a
spasm of blood vessels in the brain.
limb
An arm or a leg.
lingual
Having to do with the tongue.
linkage
The tendency for genes to be inherited
together as a package because of their location near
one another on the same chromosome.
lip
One of the two fleshy folds that surround the
opening of the mouth. The upper lip is separated
from the nose by the philtrum, the area that lies
between the base of the nose and the pigmented
edge (called the vermillion border or the carmine
margin) of the upper lip. The upper and lower lips
meet at the corners (angles) of the mouth, which
are called the oral commissures. Small blind pits
are sometimes seen at the corners of the mouth;
they are known as angular lip pits, and are consid-
ered normal minor variants. The lips may be abnor-
mally thin or thick. For example, children with fetal
alcohol syndrome typically have a thin upper lip and
flat philtrum.