What is Visual electrodiagnosis?
Visual electrodiagnosis consists of a battery of electrophysiological tests that can objectively assess the integrity of the visual function. Electrodiagnostic testing* requires some specialized equipment and a physician with expertise.
Electroretinograms (ERG’s) measure electrical activity in the retina in response to visual (light/flash or pattern) stimulation. They can be very useful and sometimes critical to the clinician when making or confirming diagnoses. Flash ERGs are not good for predicting functional vision (ie visual perception). They can provide evidence that shows that a patient's retina has impaired function, or they can provide evidence that could support the diagnosis claimed by the physician. The pattern (focal) ERG and multifocal ERGs can provide information about retinal regions with visual loss and thus could provide confirmatory evidence about visual field loss.
Visual Evoked Potentials (VEP’s) measure electrical activity at the visual cortex in response to visual (light/flash or pattern) stimuli. Pattern VEP's can be used to provide some estimation of visual acuity (VA), sensitivity to contrast (CS) and coarse information about visual fields. For the VA and CS measures the usual visual stimuli are flickering checkerboard patterns that cover large areas of the visual field. For VA estimations the size (or spatial frequency) of the checks is systematically varied, and the smallest check or stripe size for which a VEP is barely detectable gives the measure of acuity. For CS measures, the checks are coarse and the contrast is varied reduced until the VEP response becomes undetectable. The "VA" from VEP is not necessarily a good predictor of visual acuity that you would measure with letter charts or single optotypes. VEPs have the advantage that can give information about “implicit time/latency”, i.e. the delay in visual processing, which is affected in various diseases (also by pre-retinal optical processing), which might not influence VA.
For pattern stimulation (pattern ERGs and VEPs), the point of visual fixation becomes unimportant. Especially when there are significant central scotomas, there can be substantial differences between large-field grating (or checkerboard) acuity and VA measures with charts or a single optotype because with these tasks fixation and serial integration can become critically important. The measurements are performed separately for each eye.
Clinical visual electrodiagnosis follows the standards of the International Society for Clinical Electrophysiology of Vision (ISCEV).link
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*The specific visual electrodiagnostic tests are:
1. Flash full field electroretingram (ERG’s). ERG forms the standard test for the diagnosis of cone/rod dystrophies, such as retinitis pigmentosa, Leber’s amaurosis and in some cases macular dystrophies (e.g., age-related macula degeneration). The ERGs are centered to the evaluation of the integrity of the retinal photoreceptors (cones and rods) - could also separate the function of individual cone types (eg S-cones ).
2. Pattern electroretinogram (pERG's). pERG reflects the activity of the ganglion cells and assesses central (focal) vision, ie the function of the macula.
3. The multifocal electroretinogram is used to evaluate the function of the central retinal area (the 30 degrees) and therefore is useful in the diagnosis of macular diseases.
4. The Visual Evoked Potentials (VEP’s). VEP allows recording from ganglion cells and assesses the integrity of the pre-cortical visual pathway and the optic nerve.
5. The electro-ophthalmogram (EOG): EOG is used to check the integrity of the retinal pigment epithelium. It is a specialized examination for patients who suffer from Best's disease.
Relevant Publications
-Papachristou A, Lambraki A, Giannakopoulou T, Tsilimbaris MK, Plainis S. (2024) Silicone oil insulation effects on flash electroretinogram and visual evoked potential in patients with retinal detachment. Journal of Optometry. 2024;17(2):100502 doi.org/10.1016/j.optom.2023.100502
-Blavakis E, Spaho J, Chatzea M, Gleni A, Plainis S. (2023). Dichoptic Game Training in Strabismic Amblyopia Improves the Visual Evoked Response. Cureus. Sep 17;15(9):e45395. doi: 10.7759/cureus.45395
-Bontzos G, Plainis S, Papadaki E, Giannakopoulou T, Detorakis E (2018) Mechanical optic neuropathy in high myopia. Clinical and Experimental Optometry 101(4), pp. 613-5.
-Plainis S, Petratou D, Giannakopoulou T, Radhakrishnan H, Pallikaris IG, Charman EN (2013). Small-aperture monovision and the Pulfrich experience: absence of neural adaptation effects. PLoS ONE 8(10): e75987
-Diakonis VF Tsourdou A, Tzatzarakis, MN, Tsika C, Charisis S, Naoumidi I, Plainis S, Tsilimbaris MK (2013). Evaluation of Pharmacokinetics and Potential Retinal Toxicity of Intravitreal Lornoxicam (Xefo). Journal of Ocular Pharmacology and Therapeutics. 29(7): 627-632
-Tsaousis KT, Plainis S, Detorakis ET, Parry NRA, Pallikaris IG, Tsilimbaris MK (2013). Visual electrodiagnosis in Glaucoma screening: a clinical study. Journal of Glaucoma. 22(5): 427-31
-Plainis S, Petratou D, Giannakopoulou T, Radhakrishnan H, Pallikaris IG, Charman WN (2013). Interocular differences in visual latency induced by reduced-aperture monovsion. Ophthalmic and Physiological Optics. 33 (2): 123-129.
-Plainis S, Petratou D, Giannakopoulou T, Atchison DA, Tsilimbaris MK (2011). Binocular summation improves performance to defocus-induced blur. Investigative Ophthalmology and Vision Sciences. 52(5): 2784-89
-Tsilimbaris MK, Diakonis VF, Naoumidi I, Charisis S, Kritikos I, Chatzithanasis G, Papadaki T, Plainis S. (2009) Evaluation of Potential Retinal Toxicity of Adalimumab (Humira). Graefe's Archive for Clinical and Experimental Ophthalmology. 247(8): 1119-1125
-Plainis S, Murray IJ and Carden D (2006) The Dazzle Reflex; Electrophysiological signals from ocular muscles reveal strong binocular summation effects. Ophthalmic and Physiological Optics, 26: 318-325
Visual electrodiagnosis consists of a battery of electrophysiological tests that can objectively assess the integrity of the visual function. Electrodiagnostic testing* requires some specialized equipment and a physician with expertise.
Electroretinograms (ERG’s) measure electrical activity in the retina in response to visual (light/flash or pattern) stimulation. They can be very useful and sometimes critical to the clinician when making or confirming diagnoses. Flash ERGs are not good for predicting functional vision (ie visual perception). They can provide evidence that shows that a patient's retina has impaired function, or they can provide evidence that could support the diagnosis claimed by the physician. The pattern (focal) ERG and multifocal ERGs can provide information about retinal regions with visual loss and thus could provide confirmatory evidence about visual field loss.
Visual Evoked Potentials (VEP’s) measure electrical activity at the visual cortex in response to visual (light/flash or pattern) stimuli. Pattern VEP's can be used to provide some estimation of visual acuity (VA), sensitivity to contrast (CS) and coarse information about visual fields. For the VA and CS measures the usual visual stimuli are flickering checkerboard patterns that cover large areas of the visual field. For VA estimations the size (or spatial frequency) of the checks is systematically varied, and the smallest check or stripe size for which a VEP is barely detectable gives the measure of acuity. For CS measures, the checks are coarse and the contrast is varied reduced until the VEP response becomes undetectable. The "VA" from VEP is not necessarily a good predictor of visual acuity that you would measure with letter charts or single optotypes. VEPs have the advantage that can give information about “implicit time/latency”, i.e. the delay in visual processing, which is affected in various diseases (also by pre-retinal optical processing), which might not influence VA.
For pattern stimulation (pattern ERGs and VEPs), the point of visual fixation becomes unimportant. Especially when there are significant central scotomas, there can be substantial differences between large-field grating (or checkerboard) acuity and VA measures with charts or a single optotype because with these tasks fixation and serial integration can become critically important. The measurements are performed separately for each eye.
Clinical visual electrodiagnosis follows the standards of the International Society for Clinical Electrophysiology of Vision (ISCEV).link
___________________________
*The specific visual electrodiagnostic tests are:
1. Flash full field electroretingram (ERG’s). ERG forms the standard test for the diagnosis of cone/rod dystrophies, such as retinitis pigmentosa, Leber’s amaurosis and in some cases macular dystrophies (e.g., age-related macula degeneration). The ERGs are centered to the evaluation of the integrity of the retinal photoreceptors (cones and rods) - could also separate the function of individual cone types (eg S-cones ).
2. Pattern electroretinogram (pERG's). pERG reflects the activity of the ganglion cells and assesses central (focal) vision, ie the function of the macula.
3. The multifocal electroretinogram is used to evaluate the function of the central retinal area (the 30 degrees) and therefore is useful in the diagnosis of macular diseases.
4. The Visual Evoked Potentials (VEP’s). VEP allows recording from ganglion cells and assesses the integrity of the pre-cortical visual pathway and the optic nerve.
5. The electro-ophthalmogram (EOG): EOG is used to check the integrity of the retinal pigment epithelium. It is a specialized examination for patients who suffer from Best's disease.
Relevant Publications
-Papachristou A, Lambraki A, Giannakopoulou T, Tsilimbaris MK, Plainis S. (2024) Silicone oil insulation effects on flash electroretinogram and visual evoked potential in patients with retinal detachment. Journal of Optometry. 2024;17(2):100502 doi.org/10.1016/j.optom.2023.100502
-Blavakis E, Spaho J, Chatzea M, Gleni A, Plainis S. (2023). Dichoptic Game Training in Strabismic Amblyopia Improves the Visual Evoked Response. Cureus. Sep 17;15(9):e45395. doi: 10.7759/cureus.45395
-Bontzos G, Plainis S, Papadaki E, Giannakopoulou T, Detorakis E (2018) Mechanical optic neuropathy in high myopia. Clinical and Experimental Optometry 101(4), pp. 613-5.
-Plainis S, Petratou D, Giannakopoulou T, Radhakrishnan H, Pallikaris IG, Charman EN (2013). Small-aperture monovision and the Pulfrich experience: absence of neural adaptation effects. PLoS ONE 8(10): e75987
-Diakonis VF Tsourdou A, Tzatzarakis, MN, Tsika C, Charisis S, Naoumidi I, Plainis S, Tsilimbaris MK (2013). Evaluation of Pharmacokinetics and Potential Retinal Toxicity of Intravitreal Lornoxicam (Xefo). Journal of Ocular Pharmacology and Therapeutics. 29(7): 627-632
-Tsaousis KT, Plainis S, Detorakis ET, Parry NRA, Pallikaris IG, Tsilimbaris MK (2013). Visual electrodiagnosis in Glaucoma screening: a clinical study. Journal of Glaucoma. 22(5): 427-31
-Plainis S, Petratou D, Giannakopoulou T, Radhakrishnan H, Pallikaris IG, Charman WN (2013). Interocular differences in visual latency induced by reduced-aperture monovsion. Ophthalmic and Physiological Optics. 33 (2): 123-129.
-Plainis S, Petratou D, Giannakopoulou T, Atchison DA, Tsilimbaris MK (2011). Binocular summation improves performance to defocus-induced blur. Investigative Ophthalmology and Vision Sciences. 52(5): 2784-89
-Tsilimbaris MK, Diakonis VF, Naoumidi I, Charisis S, Kritikos I, Chatzithanasis G, Papadaki T, Plainis S. (2009) Evaluation of Potential Retinal Toxicity of Adalimumab (Humira). Graefe's Archive for Clinical and Experimental Ophthalmology. 247(8): 1119-1125
-Plainis S, Murray IJ and Carden D (2006) The Dazzle Reflex; Electrophysiological signals from ocular muscles reveal strong binocular summation effects. Ophthalmic and Physiological Optics, 26: 318-325
