Webster's New World Medical Dictionary

electron microscope
A microscope in which an
electron beam replaces light to form the image. An
electron microscope permits greater magnification
and resolution than an optical microscope, but the
electron densities of objects are shown rather than
their actual images. Abbreviated EM.
electron microscopy
See 
electron microscope.
electrophoresis
A method used in clinical and
research laboratories for separating molecules
according to their size and electrical charge. An
electric current is passed through a medium that
contains the mixture of molecules. Each kind of
molecule travels through the medium at a different
rate, depending on its electrical charge and molec-
ular size. Separation of the molecules occurs based
on these differences. 
electroretinography
A test in which the electri-
cal potentials generated by the retina of the eye are
measured when the retina is stimulated by light.
Abbreviated ERG. In an ERG, an electrode is placed
on the cornea at the front of the eye that measures
the electrical response of the rods and cones, the
visual cells in the retina at the back of the eye. An
ERG may be useful in the evaluation of hereditary
and acquired disorders of the retina. The instru-
ment used to conduct ERG is an electroretinograph,
and the resultant recording is called an elec-
troretinogram.
electroshock therapy
See 
electroconvulsive
therapy.
elephant nails
See 
pachyonychia congenita.
ELISA
Enzyme-linked immunosorbent assay, a
rapid immunochemical test that involves an enzyme
used for measuring a wide variety of tests of body
fluids. ELISA tests detect substances that have anti-
genic properties, primarily proteins rather than
small molecules and ions, such as glucose and
potassium. Some of these substances include hor-
mones, bacterial antigens, and antibodies. ELISA
tests are generally highly sensitive and specific, and
they compare favorably with radioimmune assay
(RIA) tests. They have the added advantage of not