In the electrophysiology laboratory of vision the following tests can be carried out:
- electroretinogram caused by diffused light (flash full field ERG)
- electroretinogram caused by visual stimulus (pattern ERG)
- visually evoked potentials (VEP) caused either by diffused light (flash VEP), or by visual stimulus (pattern VEP)
- electroculogram (EOG)
- multifocal electroretinogram (multifocal ERG)
What is the test of the electrophysiology of vision?
It is a series of recordings, through which electrical signals generated in the visual system are reflected, in response to a visual stimulus. As with the electrocardiogram, a recording of the cardiac function is made with the help of painless electrodes, the tests of the electrophysiology of vision record the retinal function (sensor of vision), and the optical path (the channel that connects the eye to the center of vision in the brain). What makes the difference is that the ECG, the electrical signals are generated automatically, while the electrodiagnostic tests are created artificially through a visual stimulus (e.g., a light in the dark). Typically, in the ophthalmic diseases, the visual system responds differently to the stimulus compared to the normal one, and this enables us to draw conclusions about a disturbance of the visual function.
What information we can get from the tests of the electrophysiology of vision?
The tests are considered as the only objective way to determine the function of the retina and visual pathway. Different electrical signals are recorded, such as those produced through different visual stimuli, in different cells and structures of the optical pathway. In a visual system carrying a disturbance, the electrical signals can be smaller in size or be delayed related to the normal.
What is the procedure related to these tests? Can they cause pain?
As in the electrocardiogram, we place electrodes on the skin around the eyes. These electrodes are like small antennas that have the ability to detect minimal electrical signals. It is adhesive and do not cause pain. In the ERG test, it will be needed to cause mydriasis (pupil dilation) with eyedrops, and place an electrode in contact with the cornea (the front surface of the eye). During these tests we use a variety of visual stimuli (eg lights, pictures) and we record, with the help of special programmes in the computer, the way the visual system responds.
How long do they last?
The duration of each test varies, but, typically, they take about 45-60 minutes.
What do I need to do to prepare for these tests?
- to have all relevant information from previous examinations in the eye (vision, visual fields, fluorescein angiography, etc.) with you
- to carry your vision spectacles
- If you plan to come by car, you will need to bring along someone who will drive back after the examination
- carry your sunglasses with you
- the skin around the eye should be clean. Avoid using make-up. If you schedule the evoked potentials test, you should have bathed earlier
Indications for the electrophysiological study
Indications for the electrophysiological study:
- dystrophies of the retina (retinitis pigmentosa, partial, perivenous, unilateral pigmented retinopathy, carriers of x-linked retinitis pigmentosa, syndromes and retinitis pigmentosa, such as usher syndrome)
- congenital amaurosis of leber
- late-onset retinal dystrophy
- chorioeiderimia, x-linked entities
- reinforced cone syndrome
- cone dystrophies
- retinal spots syndromes
- stargardt disease for classification and prognosis
- color blindness
- Congenital non-progressive nyktalopia
- best disease and autosomal recessive bestrophinopathy
- adult viteliform macula dystrophy
- autoimmune retinopathies, retinopathy associated with cancer, melanoma-associated retinopathy
- uveitis involving the retina
- AZOOR, AMNR, EBSS
- toxicity of drugs such as isotretinoin, hydroxychloroquine, rifabicyn, desferioxamine
- patient assessment with no clear refractive media (cataracts, clouding of the cornea)
- unexplained vision loss
- unexplained symptoms such as scotoma and flashes that are not explained by the clinical examination
- thyroid disease with unexplained vision loss
- multiple sclerosis
Indications for electrophysiology in children
- serious refractive error
- optic pathway function study
- retinal function study
- sensorineural hearing loss to usher syndrome exclusion
- amblyopia that does not meet the eye coverage