Visual Electrophysiology Diagnostic Laboratory
Information for patients can be easily viewed on our
Laboratory Brochure.
Our services at our satellite office, Eye Institute East, at 404 Portland Street
behind Columbia Regional Hospital, include non-invasive visual function tests for
patients such as electroretinogram (ERG), visual evoked potential (VEP) and electro-oculogram
(EOG). As integrated parts of ophthalmology examination, these tests will provide
important and objective information for eye disease diagnosis, prognosis and treatment.
Visual electrophysiology appointments are scheduled for Friday mornings between
8:00 and 11:50 a.m. Please call (573) 882-8920 to schedule an appointment.
Frequently Asked Questions
What are visual electrophysiology diagnosis tests?
Visual electrophysiology diagnostic tests contain a family of noninvasive recordings
which measure electrical signals that occur in the visual system in response to
visual stimulation. Like electrocardiogram (ECG or EKG) which tests the heart function,
the visual electrophysiology tests (including ERG, EOG and VEP) will tell you how
well your retina and optic nerve work. What different is ECG signals are generated
spontaneously while most of the visual electrophysiology tests are evoked potentials,
which means to get these responses, a visual stimulation such as light is needed.
Usually, normal eye and disease eye react differently to the stimulation, and we
can therefore deduce the eye function.
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What information can visual electrophysiology diagnostic tests provide?
The visual electrophysiology diagnostic tests reflect retinal, optic nerve and visual
pathway way function, and provide important information for ocular disease diagnosis
and treatment. Currently, it is regarded as the only objective way to determine
the function of the retina and visual pathway.
The electrical signals in the visual system elicited by different visual stimuli
are recorded. These voltage changes vary with time and can be plotted as a waveform.
The terms
implicit time (latency) and amplitude describe the timing (in m/sec)
and size (in micro volts) respectively. The complex electrophysiological waveforms
consist of those positive and negative signals which are generated from different
cells. Normal neuron or non-neuronal cells generate responses within a range, while
in a diseased eye these signals may be smaller in size and slower in timing.
On an ERG, for example, by analysing the changes of the a-, b-wave and other components,
we can tell if photoreceptors (rods and cones), bipolar cells (on- and off-center),
or other cells in the inner retina (amacrine cells) are affected.
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What tests will I/my patient need?
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Summary of Potential Indications for Specific Tests
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Provisional Diagnosis
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Inherited retinal dystrophies
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Vascular diseases including diabetes
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Opaque media or trauma
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Retrobulbar neuritis
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Unexplained visual loss
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Infant with questionable vision
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Albinism
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Toxic and nutritional eye disease
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Glaucoma
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Suspected intracranial lesion
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What tests we can do at Mason Eye Institute?
The tests include electroretinogram (ERG) to assesses the aggregate response of
the retina, visual evoked potential (VEP), a response evoked from the visual cortex,
and electro-oculogram (EOG). ERG and VEP can be further divided into subcategories
based on the stimulation used. Responses elicited with flash stimulation are termed
flash ERG (FERG) and flash VEP (FVEP), and responses react to pattern stimulation
are named pattern ERG (PERG) and pattern VEP (PVEP).
Based on the results of your other ocular examinations, your doctor will decide
which test(s) you will need.
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What information does Mason Eye Institute need when test(s) are requested?
Please provide us with related complimentary data as complete as possible. This
is very helpful in selecting the appropriate tests and in the results interpretation.
For patients who are referred for investigation, this is extremely important.
The most important complimentary data are listed below:
- Chief complaint
- Major ocular examination findings
- Visual acuity
- Visual fields
- Dark adaptation
- Color vision
- Pupillography
- Ultrasound B
- Intraocular pressure
- Genetic counseling
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What are the test procedures and how long will the tests take?
During all the tests, we will attach two to five electrodes to the skin around the
eye, on the ear lobe or on the head. These electrodes are non-invasive, painless,
and will measure electric responses.
During and ERG test, the pupil will be dilated and a special corneal contact lens
electrode will be placed. The patient will then be dark-adapted in dark room for
approximately 30-40 minutes.
During the tests, different light stimulation such as light flashes will be used
and the response of your eyes to the stimulation will be recorded. After the test,
the report will be forwarded to your doctor.
Time needed to complete the tests varies. The following are average times based
on previous tests performed. In the case of testing on children under 6 years, multiply
the estimated time by 1.5.
- Standard ERG: 60 minutes (40 minutes dark adaptation plus pupil dilation)
- Flash or Pattern VEP: 30-45 minutes
- EOG: 45-60 minutes
- Pattern ERG: 30 minutes
- Special VEP: 30-60 minutes
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What do I need to prepare for the tests?
- Plan on arriving 15 minutes before your scheduled test time in order to fill out
necessary paperwork.
- If possible, bring along all relevant information from past examinations, especially
eye examination results (vision, color vision, visual field, dark adaptation, funduscopic
photographs, fluorescien angiographies, etc.).
- Bring your prescription eyeglasses.
- Patients scheduled for an ERG test will have their pupils dilated. IF YOU HAVE GLAUCOMA,
PLEASE LET US KNOW.
- If you are concerned about driving home after dilation, please arrange to have someone
drive you. BRING SUNGLASSES.
- Keep head skin clean (especially around the eye and ear lobe) and do not use makeup.
If you are scheduled for a VEP test, wash hair beforehand.
For more information about visual electrophysiology diagnostic tests, please contact:
- Christina McKenzie at (573) 882-8920, or Bo Lei, PhD, MD.
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