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Questions and Answers
Electrophysiology is the study of biological cells and tissues.
True
Electro-occulogram (EOG) examines the function of the optic nerve.
False
Electro-retinogram (ERG) reflects the functions of the photoreceptors and outer nuclear layers of the Retina.
False
Visual Evoked potential (VEP) measures electrical activity in the visual cortex in response to eye movement.
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The front part of the globe generates a positive standing potential in the eye.
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Electro-retinogram (ERG) is a mass response evoked by the entire retina with a brief stimulus of sound.
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Visual Evoked potential (VEP) is related to the transmission of nervous impulses from the cornea to the brain.
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Electro-occulogram (EOG) examines the function of photoreceptors in the Retina.
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Electroretinography (ERG) is used to assess the functions of Retinal pigment epithelium (RPE).
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Visual Evoked potential (VEP) involves measuring electrical activity in areas 15, 16, and 17 of the visual cortex.
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Study Notes
Electroretinogram (ERG)
- The normal light peak to dark trough ratio (Arden ratio) is at least 1.85.
- ERG measures the electrical response of the light-sensitive cells (rods and cones) in the eyes.
- Cones are responsible for the eye's color sensitivity.
- Rods are more sensitive to light than cones.
ERG Procedure
- Patient lies down or sits in a comfortable position.
- Eyes are dilated and anesthetic drops are placed to numb them.
- Retractors are used to hold eyelids open.
- A small electrode is placed on each eye, which can be about the size of a contact lens or a fine thread on the cornea.
- Another electrode is attached to the skin as a ground for the faint electrical signals made by the retina.
- The test is conducted in normal light and in a darkened room.
ERG Results
- Electrical responses recorded in a light room mainly come from cones.
- Responses recorded in a darkened room mainly come from rods.
- The recorded information appears as a-waves and b-waves.
- The a-wave is a positive wave that originates mainly from the cornea, representing the initial negative deflection of a flash of light measuring rods and cones.
- The b-wave, or positive deflection, follows, and its amplitude reveals how well the eye reacts to light.
Indications for ERG
- ERG can be requested to determine if there is an inherited or acquired disorder of the retina, such as: • Retinitis pigmentosa • Macular degeneration • Retinoblastoma • Retinal separation • Cone Rod dystrophy (CRD)
- ERG may also help in the assessment for retinal surgery or other types of eye surgery, such as cataract removal.
Visual Evoked Potential (VEP)
- VEP is an electrophysiologic response recorded from the scalp in response to stimulation by either patterned or unpatterned visual stimuli.
- The generator site for VEP is believed to be the peristriate and striate occipital cortex.
- It is an objective technique that helps in the clinical assessment of the functional state of the visual system beyond the retinal ganglion cells.
- There are three types of VEP: Flash VEP, Pattern reversal VEP, and Pattern onset/offset VEP.
Electrophysiology in Ocular Pathologies
- Electrophysiology provides objective information in relation to visual pathways to aid diagnosis and management of patients.
- Role of electrophysiology: • Assessment of functions of the visual pathway • Make early diagnosis • Study potential toxicity of the visual system • Objective functional assessment and documentation of efficacy of treatment
Types of Electrophysiology Tests
- Electro-oculogram (EOG): examines the function of the Retinal pigment epithelium (RPE) interaction with photoreceptors
- Electro-retinogram (ERG): measures the retinal electrical potential elicited by visual stimulation
- Visual Evoked potential (VEP): measures the electrical activity in the visual cortex in response to stimulation of the eye
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Description
Learn about EOG and Electroretinogram (ERG) tests that measure the electrical response of light-sensitive cells in the eyes. Understand the normal Arden ratio and the differences between cones and rods in eye sensitivity.
