Electrooculography (EOG) is a specialized diagnostic procedure used to assess the retina’s functional state called the retinal pigment epithelium (RPE) and to study ocular motions. It is a valuable tool in ophthalmology and neurology which gives a crucial information on both retinal and extraocular diseases. This approach is based on detecting and recording the corneo-retinal potential (CRP). It is a bioelectric phenomenon caused by the eye’s dipole nature. The cornea has a higher positive charge than the retina and this potential varies with eye movement and light conditions. EOG’s capacity to quantify these changes makes it a helpful diagnostic tool for a variety of clinical applications. This measures the CRP which exists between front and back of the human eye. The result signal is known as electrooculogram. The EOG is ranging from 0.05 mV to 3.5 mV in human. It is linearly proportional to displacement of eye.
The distribution of ions in the eye’s tissues causes it to operate as an electrical dipole. The cornea which is more positively charged than the retina creates a constant potential difference known as the eye’s standing potential. The activity of the RPE and the outer segments of photoreceptor cells impact this potential.
Under typical circumstances, the standing potential fluctuates with variations in ambient illumination. When the eyes are exposed to light, the RPE experiences metabolic and ionic changes which leads to change in the CRP. During dark adaptation, the potential shifts as the retina and RPE respond to lower light levels. EOG detects these differences by detecting the electrical impulses produced during eye movements.
EOG is a safe and non-invasive procedure suitable for different patients like children and those who have comorbidities. It evaluates the functional status of the retina and RPE unlike structural imaging. EOG can be used as a complementary tool with other tests like ERG or OCT. EOG data are not specific to a particular disease and must be interpreted with clinical and imaging results. External factors like illumination and patient cooperation might alter the accuracy of results. Accurate interpretation needs the highest quality equipment and skilled operators.
Indications
To evaluate the retinal function: EOG evaluates RPE function and photoreceptor activity. It is used in combination with ERG for comprehensive retinal health assessment.
To diagnosis of Vitelliform Macular Dystrophy (BVMD): EOG is important to diagnose this autosomal dominant macular dystrophy.
Pattern Dystrophies of the retina: EOG used to diagnose and monitor these dystrophies.
Age-Related Macular Degeneration (AMD): It is used to detect the early functional changes in AMD patients.
To diagnose ocular and neurological disease: It is used in different ocular and neurological diseases in oculomotor or visual abnormality is present.
Choroidal dystrophies: Inherited disease which can affect the choroid and retinal pigment epithelium may be evaluated by using EOG.
Stargardt disease: This juvenile macular degeneration may lead to change in EOG results and help in differential diagnosis.
Retinitis Pigmentosa (RP): By evaluating the function of retinal pigment epithelium, EOG helps ERG in diagnosis of RP.
Progressive Supranuclear Palsy (PSP): EOG is used to study saccadic and smooth pursuit eye movements which are impaired in PSP.
Parkinson’s Disease: Abnormalities in saccadic latency and amplitude is assessed by EOG.
Multiple Sclerosis (MS): MS may cause optic nerve dysfunction which can change the EOG results in combination with other visual function tests.
To assess the oculomotor function: EOG gives insights into eye movement dynamics.
Saccadic eye movements: Diseases which can affect rapid, ballistic eye movements is evaluated by using EOG.
Smooth pursuit movements: Diseases that impair the ability to track moving objects smoothly can be assessed by EOG.
Fixation stability: EOG helps to analyze fixation abnormalities in conditions like amblyopia or nystagmus.
Benign Paroxysmal Positional Vertigo (BPPV): EOG can help to assess nystagmus patterns during positional testing.
Meniere’s Disease: Abnormalities in eye movements because of inner ear dysfunction is assessed by using EOG.
Vestibular Neuritis: EOG helps to evaluate compensatory eye movements which is caused by vestibular asymmetry.
Congenital Stationary Night Blindness (CSNB): EOG is used to differentiate CSNB from other retinal dystrophies.
Albinism: EOG can help to detect functional abnormalities in the retina and optic nerve pathways linked with albinism.
Contraindications
Absolute Contraindications:
Severe ocular surface disorders: Conditions which compromise the integrity of the ocular surface can cause discomfort and increase symptoms during electrode placement or exposure to light stimuli.
Active ocular infections: EOG should be avoided in cases of active infections to prevent exacerbation or spread.
Allergy to electrode material or conductive gel: Patients with known hypersensitivity to materials used in the electrodes or the conductive gel required for the test are contraindicated.
Relative Contraindications:
Inability to maintain required eye movements: Patients who are unable to comply may not give reliable results.
Severe photophobia: Exposure to alternating light and dark conditions may be intolerable for patients with extreme sensitivity to light.
Acute eye trauma: Recent trauma to the eye or surrounding structures can make EOG testing impractical or harmful.
Epilepsy or photosensitive seizures: EOG involves alternating light stimuli which can trigger seizures in photosensitive individuals.
Skin conditions around the eyes: Conditions affecting this area may hinder electrode placement or cause discomfort.
Uncontrolled eye movements: Conditions causing involuntary eye movements may interfere with the ability to perform the required tasks for EOG.
Pacemaker or implanted electronic devices: Concerns about interference from EOG equipment may be considered.
Outcomes
Equipment
Electrodes like surface or cup electrodes: It detect the electric signals generated by eyes. 2 electrodes are used.
Conductive gel: It is applied on the electrodes to makes sure proper contact with the skin.
Amplifier: The electric signals which are weak and must be amplified for recording and analysis.
Light source like ganzfeld dome or LED light box: A controlled light source is essential for stimulating the eyes during the test
Patient preparation
Medical history review and patient counseling: Identify contraindications or conditions affecting test results. Discuss history of eye diseases, current medications, photosensitivity, epilepsy and skin allergies.
Patient counselling: Provide clear explanation of the test, purpose, duration and expectations. Obtain informed consent and emphasize cooperation and comfort.
Pre-test instructions: Advise removal of eye makeup or lotions. Instruct removal of contact lenses. Avoid caffeine or alcohol for 24 hours before the test. Encourage good sleep hygiene to minimize fatigue.
Skin preparation: Clean areas around eyes, forehead and earlobe. Allow air drying before placing electrodes.
Adjust the environment: Conduct the test in a dimly lit or controlled light environment. Make sure comfortable room temperature to prevent distractions or discomfort.
Patient position
The patient should be seated in a comfortable chair with a backrest using head support like a chin rest or forehead strap. The patient’s head should be upright and aligned with the light source or fixation target. For patients who cannot sit upright, a reclined or semi-reclined position may be used. Adequate head and neck support is necessary for stability. The fixation point should be at the patient’s eye level for comfortable movements and a standard distance of 30 to 50 cm for consistent results.
Technique
Step 1: Patient preparation:
The patient’s skin is cleaned with alcohol swabs or a mild cleanser to remove oils or debris and a conductive gel is applied for improved electrical conductivity. Surface electrodes are placed symmetrically with one on the lateral canthus of each eye, a reference electrode on the forehead or earlobe and a ground electrode on the hand or forearm. The testing room is adjusted to minimize light and electrical noise.
Step 2: Calibration:
The patient’s eye movements and electrical potentials are recorded through calibration with initial measurements taken to establish the baseline electrical potential. The recording equipment is adjusted to minimize noise and optimize signal quality with the patient fixed on lighted targets at fixed intervals.
Step 3: Light and dark adaption technique:
The study evaluates the retinal pigment epithelium’s response to different lighting conditions. The patient is placed in a dark room or Ganzfeld dome for 10 to 20 minutes while then exposed to uniform light for 10 to 15 minutes with brightness levels controlled to prevent overstimulation or discomfort.
Step 4: Eye movement recording:
The patient is instructed to alternate gaze between 2 lighted targets typically 20 to 30° apart to measure electrical potential. Repeated movements are recorded to ensure consistency. The patient’s focus is maintained on a single point while the electrical potential is measured. Dynamic tasks may involve following a moving light or performing specific eye movement patterns to evaluate oculomotor control.
Step 5:Signal amplification and filtration:
The eyes’ microvolt range electrical signals are amplified using a differential amplifier to avoid distortion and preserve waveform integrity. Signal filtering is applied to remove artifacts from muscle activity, blinking or ambient electrical noise like low-pass filters for high-frequency noise, high-pass filters for baseline drift or low-frequency noise and notch filters for mains power interference.
Step 6: Data analysis:
The waveform analysis involves identifying the maximum potential during light adaptation and the minimum potential during dark adaptation. The Arden Ratio is calculated to assess RPE function typically above 1.8. Techniques like signal averaging or manual review are used to remove artifacts from blinking, head movements or electrode displacement.
Step 7: Post procedure care:
Electrodes are gently removed and conductive gel is wiped off with a damp cloth or cotton pad. Preliminary results are reviewed for completeness and signal quality before final analysis and specific segments may be repeated if needed.
Complications
Eye irritation or discomfort
Skin irritation at electrode sites
Infection
Inaccurate result because of improper electrode placement
Electrooculography (EOG) is a specialized diagnostic procedure used to assess the retina’s functional state called the retinal pigment epithelium (RPE) and to study ocular motions. It is a valuable tool in ophthalmology and neurology which gives a crucial information on both retinal and extraocular diseases. This approach is based on detecting and recording the corneo-retinal potential (CRP). It is a bioelectric phenomenon caused by the eye’s dipole nature. The cornea has a higher positive charge than the retina and this potential varies with eye movement and light conditions. EOG’s capacity to quantify these changes makes it a helpful diagnostic tool for a variety of clinical applications. This measures the CRP which exists between front and back of the human eye. The result signal is known as electrooculogram. The EOG is ranging from 0.05 mV to 3.5 mV in human. It is linearly proportional to displacement of eye.
The distribution of ions in the eye’s tissues causes it to operate as an electrical dipole. The cornea which is more positively charged than the retina creates a constant potential difference known as the eye’s standing potential. The activity of the RPE and the outer segments of photoreceptor cells impact this potential.
Under typical circumstances, the standing potential fluctuates with variations in ambient illumination. When the eyes are exposed to light, the RPE experiences metabolic and ionic changes which leads to change in the CRP. During dark adaptation, the potential shifts as the retina and RPE respond to lower light levels. EOG detects these differences by detecting the electrical impulses produced during eye movements.
EOG is a safe and non-invasive procedure suitable for different patients like children and those who have comorbidities. It evaluates the functional status of the retina and RPE unlike structural imaging. EOG can be used as a complementary tool with other tests like ERG or OCT. EOG data are not specific to a particular disease and must be interpreted with clinical and imaging results. External factors like illumination and patient cooperation might alter the accuracy of results. Accurate interpretation needs the highest quality equipment and skilled operators.
To evaluate the retinal function: EOG evaluates RPE function and photoreceptor activity. It is used in combination with ERG for comprehensive retinal health assessment.
To diagnosis of Vitelliform Macular Dystrophy (BVMD): EOG is important to diagnose this autosomal dominant macular dystrophy.
Pattern Dystrophies of the retina: EOG used to diagnose and monitor these dystrophies.
Age-Related Macular Degeneration (AMD): It is used to detect the early functional changes in AMD patients.
To diagnose ocular and neurological disease: It is used in different ocular and neurological diseases in oculomotor or visual abnormality is present.
Choroidal dystrophies: Inherited disease which can affect the choroid and retinal pigment epithelium may be evaluated by using EOG.
Stargardt disease: This juvenile macular degeneration may lead to change in EOG results and help in differential diagnosis.
Retinitis Pigmentosa (RP): By evaluating the function of retinal pigment epithelium, EOG helps ERG in diagnosis of RP.
Progressive Supranuclear Palsy (PSP): EOG is used to study saccadic and smooth pursuit eye movements which are impaired in PSP.
Parkinson’s Disease: Abnormalities in saccadic latency and amplitude is assessed by EOG.
Multiple Sclerosis (MS): MS may cause optic nerve dysfunction which can change the EOG results in combination with other visual function tests.
To assess the oculomotor function: EOG gives insights into eye movement dynamics.
Saccadic eye movements: Diseases which can affect rapid, ballistic eye movements is evaluated by using EOG.
Smooth pursuit movements: Diseases that impair the ability to track moving objects smoothly can be assessed by EOG.
Fixation stability: EOG helps to analyze fixation abnormalities in conditions like amblyopia or nystagmus.
Benign Paroxysmal Positional Vertigo (BPPV): EOG can help to assess nystagmus patterns during positional testing.
Meniere’s Disease: Abnormalities in eye movements because of inner ear dysfunction is assessed by using EOG.
Vestibular Neuritis: EOG helps to evaluate compensatory eye movements which is caused by vestibular asymmetry.
Congenital Stationary Night Blindness (CSNB): EOG is used to differentiate CSNB from other retinal dystrophies.
Albinism: EOG can help to detect functional abnormalities in the retina and optic nerve pathways linked with albinism.
Absolute Contraindications:
Severe ocular surface disorders: Conditions which compromise the integrity of the ocular surface can cause discomfort and increase symptoms during electrode placement or exposure to light stimuli.
Active ocular infections: EOG should be avoided in cases of active infections to prevent exacerbation or spread.
Allergy to electrode material or conductive gel: Patients with known hypersensitivity to materials used in the electrodes or the conductive gel required for the test are contraindicated.
Relative Contraindications:
Inability to maintain required eye movements: Patients who are unable to comply may not give reliable results.
Severe photophobia: Exposure to alternating light and dark conditions may be intolerable for patients with extreme sensitivity to light.
Acute eye trauma: Recent trauma to the eye or surrounding structures can make EOG testing impractical or harmful.
Epilepsy or photosensitive seizures: EOG involves alternating light stimuli which can trigger seizures in photosensitive individuals.
Skin conditions around the eyes: Conditions affecting this area may hinder electrode placement or cause discomfort.
Uncontrolled eye movements: Conditions causing involuntary eye movements may interfere with the ability to perform the required tasks for EOG.
Pacemaker or implanted electronic devices: Concerns about interference from EOG equipment may be considered.
Electrodes like surface or cup electrodes: It detect the electric signals generated by eyes. 2 electrodes are used.
Conductive gel: It is applied on the electrodes to makes sure proper contact with the skin.
Amplifier: The electric signals which are weak and must be amplified for recording and analysis.
Light source like ganzfeld dome or LED light box: A controlled light source is essential for stimulating the eyes during the test
Patient preparation
Medical history review and patient counseling: Identify contraindications or conditions affecting test results. Discuss history of eye diseases, current medications, photosensitivity, epilepsy and skin allergies.
Patient counselling: Provide clear explanation of the test, purpose, duration and expectations. Obtain informed consent and emphasize cooperation and comfort.
Pre-test instructions: Advise removal of eye makeup or lotions. Instruct removal of contact lenses. Avoid caffeine or alcohol for 24 hours before the test. Encourage good sleep hygiene to minimize fatigue.
Skin preparation: Clean areas around eyes, forehead and earlobe. Allow air drying before placing electrodes.
Adjust the environment: Conduct the test in a dimly lit or controlled light environment. Make sure comfortable room temperature to prevent distractions or discomfort.
Patient position
The patient should be seated in a comfortable chair with a backrest using head support like a chin rest or forehead strap. The patient’s head should be upright and aligned with the light source or fixation target. For patients who cannot sit upright, a reclined or semi-reclined position may be used. Adequate head and neck support is necessary for stability. The fixation point should be at the patient’s eye level for comfortable movements and a standard distance of 30 to 50 cm for consistent results.
Step 1: Patient preparation:
The patient’s skin is cleaned with alcohol swabs or a mild cleanser to remove oils or debris and a conductive gel is applied for improved electrical conductivity. Surface electrodes are placed symmetrically with one on the lateral canthus of each eye, a reference electrode on the forehead or earlobe and a ground electrode on the hand or forearm. The testing room is adjusted to minimize light and electrical noise.
Step 2: Calibration:
The patient’s eye movements and electrical potentials are recorded through calibration with initial measurements taken to establish the baseline electrical potential. The recording equipment is adjusted to minimize noise and optimize signal quality with the patient fixed on lighted targets at fixed intervals.
Step 3: Light and dark adaption technique:
The study evaluates the retinal pigment epithelium’s response to different lighting conditions. The patient is placed in a dark room or Ganzfeld dome for 10 to 20 minutes while then exposed to uniform light for 10 to 15 minutes with brightness levels controlled to prevent overstimulation or discomfort.
Step 4: Eye movement recording:
The patient is instructed to alternate gaze between 2 lighted targets typically 20 to 30° apart to measure electrical potential. Repeated movements are recorded to ensure consistency. The patient’s focus is maintained on a single point while the electrical potential is measured. Dynamic tasks may involve following a moving light or performing specific eye movement patterns to evaluate oculomotor control.
Step 5:Signal amplification and filtration:
The eyes’ microvolt range electrical signals are amplified using a differential amplifier to avoid distortion and preserve waveform integrity. Signal filtering is applied to remove artifacts from muscle activity, blinking or ambient electrical noise like low-pass filters for high-frequency noise, high-pass filters for baseline drift or low-frequency noise and notch filters for mains power interference.
Step 6: Data analysis:
The waveform analysis involves identifying the maximum potential during light adaptation and the minimum potential during dark adaptation. The Arden Ratio is calculated to assess RPE function typically above 1.8. Techniques like signal averaging or manual review are used to remove artifacts from blinking, head movements or electrode displacement.
Step 7: Post procedure care:
Electrodes are gently removed and conductive gel is wiped off with a damp cloth or cotton pad. Preliminary results are reviewed for completeness and signal quality before final analysis and specific segments may be repeated if needed.
Complications
Eye irritation or discomfort
Skin irritation at electrode sites
Infection
Inaccurate result because of improper electrode placement
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