Section 30. Disorders of the Eyes >
Part 1. General Principles >
Chapter 581. Special Tests of the EyesDaniel J. Karr and Alex V. Levin
Topics Discussed: electroretinography; ophthalmic examination and evaluation; ophthalmology.
Sections: Electrooculography (EOG), Visual Evoked Potential (VEP), Visual Field Testing, Ultrasonography, Optical Coherence Tomography (OCT), Intravenous Fluorescein Angiography, References.
Excerpt:"The electroretinogram (also known as full-field ERG)
is a measure of retinal photoreceptor integrity and thus retina
function. The basic technique consists of measuring the action potential
produced by the retina when stimulated by light of variable intensity
and color. ERG allows differentiation between the responses of the
retinal rod and cone systems. A contact lens with an imbedded electrode
is placed on the cornea, or a skin electrode is placed on the lower
lid. A reference skin electrode is placed on the forehead. The ERG
can be performed awake in infancy and later childhood but usually
requires sedation or general anesthesia between the ages of 1 and
6 years. The first step of the ERG is dark adaptation, which is
done by double patching both eyes for at least 20 minutes. Then,
in a completely dark environment, the test is started. Sleeping
or awake, quiet infants and children under sedation or anesthesia
lie supine while the bowl-shaped machine is brought over their face.
Older children can sit upright and their chin is placed on a rest
within the bowl. As variable light stimuli are presented within
the bowl, the electrical potential between electrodes is then measured
and recorded as a waveform. In anxious children dim light adaptation
(mesoptic vision) can be substituted.The multifocal ERG results in a topographical three-dimensional
map of retinal function and is used to assess retinal function in
much smaller areas than possible with full-field ERG. For example,
the mfERG can..."
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