CLINICAL CLINICAL ELECTROPHYSIOLOGY OF ELECTROPHYSIOLOGY OF VISIONVISION

klllhh

Manish DahalBSc. Optm 3rd year

MANISH DAHAL, BSc. OPTM. 3rd YEAR

BELIEVE YOU CAN & YOU ARE HALF WAY THERE

CASE HISTORYCASE HISTORY A 20 years old male presented with chief complaint of slow, Painless progressive vison loss at distance and near. He

reported that vision was poor since 10 yrs of age and his other symptoms was photophobia.

PATIENT HISTORYNO any medical and family ocular history.

DIAGNOSTIC DATADIAGNOSTIC DATA VISUAL ACUITY 20/200 OU PUPIL was round and refractive to light EOM was normal Anterior segment was normal Dilated fundus revealed clear vitreous & relatively large

optic nerve with moderate size cups OU CONFRONTATION visual field were full to finger counting

OU

OD OS

RETINA QUIZ1) What simple , in- office test would provide the most useful

informtaion about our patient? a)applanation tonometry b) amsler grid c)color vision testing ++ d) manifest refraction

2) What additional test is necessary to help confirm the diagnosis?

a)ERG ++ b) EOG c) FA d)Visual field

3) How do you interpret the SD-OCT? a) normal b) abnormally thick choroid c) loss of photoreceptor integrity line ++ d) Occult

choroidal neovascularisation

4) What is the most likely diagnosis?a) Cone dystrophy++b)Stargardt’s macular dystrophyc) Malingeringd)Functional vision lossDISCUSSIONThe dilated fundus exam of our patient

showed essentially normal optic nerve and a healthy macula, foveal light reflex was present in each eye.

So, what was wrong with our patient??Did he have some form of functional

visual loss or was he malingering?The answer was embedded in case

history.One of his complaint was photosensitivity.

He said his vision was better at night or when the light was dimmer. He didn’t see well in normal lighting.

CB couldn’t read 15 plates of ishihara color vision testing

At this point all clue suggested that the patient had cone dystrophy.

Cone dystrophy is acquired disorder that affect cone photoreceptor. It tends to be progressive in nature and is acquired later in life –unlike other congenital photorecptor conditions, such as achromatopsia , nystagmus and varying degree of color vision

There are several hereditary pattern of acquired cone dystrophy- all of which result in early loss of color vision aswell as progressive loss in visual acuity[ to the level of 20/200- 20/400]

In most cases vision loss begins during teenage years, however initial symptoms may be present in late 7th decade. Intrestingly our patient was first seen at the age of 15 VA being 20/60 OU

In our patient the retinal exam appear normal- although we could convince that there had been temporal optic nerve pallor

The wide variety of clinical presentation illustrate why electrophysiology is so important in confirming the diagnosis

ERG was performed which revealed significantly reduced and prolonged cone response and mildly reduced rod response that was consistent with an acquired cone dystrophy.

The SD-OCT is quite intresting. At first glanCe it appears normal. However on careful inspection, we can see PIL is absent in fovea which suggest that a process is affecting photoreceptor

There are number of hereditary pattern for cone dystrophy including autosomal dominant, recessive and x- linked .

The patient family history was negative for cone dystrophy so, it is likely that his condition was autosomal recessive in nature

Finally the patient was referred to low vision service evaluation

The above case shows how important is electrophysiology in diagnostic procedure much before than an ophthalmoscopic finding.

ElectrophysiologyElectrophysiology

Electrophysiology is electrical phenomena associated with a physiological process.

Electrophysiology tests record the electrical responses generated by the eyes or visual cortex

Electrophysiology is objective test that helps in evaluation of retinal function.

Common Visual Electrodiagnostic TestsCommon Visual Electrodiagnostic Tests ERG (Electroretinogram)

– Ganzfeld– Pattern– Multifocal

EOG (Electro-oculogram) VEP/VER (Visual Evoked Potential/Response)

– Pattern– Flash

ERG: Functional Testing of RetinaERG: Functional Testing of Retina

A flash of light will elicit an electrical response from the retina

The response can be recorded by placing electrodes on the surface of eye

The recorded response is weak and needs to be amplified

Recorded data can be stored and analyzed on a computer

Recording Electrode

Amp.Reference Electrode

ComputerEar

Ground Electrode

ERG Recording Setup

Ganzfeld Dome

ERG Response

Typical ERG ResponseTypical ERG Response A-Wave: Mostly due to Photoreceptor activity (outer

retina) B-wave: Mostly due to On- and Off- Bipolar and

Müller cell activity (inner retina)

Scotopic 0 dB Flash

-500

-400

-300

-200

-100

0

100

200

300

0 25 50 75 100 125 150

Electroretinogram 1:

(µV

) Od

milliseconds

B-Wave

A-Wave

Full Dilatation 30’ Dark adaptation for scotopic and 10’ light adaptation

for phototopic response Avoid FFA or fundus photography before ERG. If done 1

hour dark adaptation is must Fixation to prevent artifacts Connect the electrodes:

– Corneal electrodes on eyes– Reference electrode on forehead– Ground on ear

ERGERG:: Test Procedure Test Procedure

ERGERG:: Recording ElectrodesRecording Electrodes

ERG-Jet Burian-Allen DTL

Commonly used corneal electrodes:

Helps Diagnose:– Retinitis Pigmentosa and other inherited retinal degenerations– Congenital and acquired night blindness– Inflammatory conditions (AZOOR, MEWDS)– Vitamin A deficiency

Helps Manage:– Diabetic Retinopathy– Central and Branch Vein or Artery Occlusion– Monitor retinal toxicity of drugs such as Plaquenil, Quinine,

Cisplatin, Vigabatrin Helps Prognosis:

– Ocular trauma– Detached Retina

ERG: Clinical ApplicationsERG: Clinical Applications

ERG: Additional TestsERG: Additional Tests Pattern ERG

– Important point: Patient need to be refracted using tri-lenses. Use temporal fossa for reference electrode, and forehead for ground electrode.

– Recording electrode: DTL or Gold Foil Electrode (no lens electrode)

– Generated by retinal ganglion cells– Glaucoma evaluation– Macular dysfunction

Very bright flash (+25dB) test for pre-operative evaluation– Dense cataract– Vitreous hemorrhage

ERG: Additional TestsERG: Additional Tests Photopic Negative Response ERG

– Test condition: Dilated, photopic test– Stimulus: Red Flash on Blue Background– Generated by retinal ganglion cells– Early glaucoma evaluation

On/Off Response ERG– Test condition: Dilated, photopic test– Stimulus: Red Flash on Blue Background– Looking at On and Off Bipolar Cells responses– Inner retina dysfunction

S-Cone ERG– Test condition: Dilated, photopic test– Stimulus: Blue Flash on Amber background– Generated by S-Cone Photoreceptors– Enhanced S-Cone Syndrome

ERG: Additional Tests - ResearchERG: Additional Tests - Research

Scotopic Threshold response ERG– Test condition: Dilated, scotopic test– Stimulus: Series of flash of increasing intensity

starting from below threshold (starting intensity is species dependent)

Double Flash ERG– Stimulus: Bright Flash followed by medium

flash

EOG: The Electro-OculogramEOG: The Electro-Oculogram

Records the standing potential between the front and back of eye

Also called “Corneo-Fundal Potential” Measures function of Retinal Pigment Epithelium (RPE) Amplitude of potential changes with retinal illumination

over a period of minutes– Dark: smaller potential– Light: larger potential

EOG Testing: First StepsEOG Testing: First Steps

Connect electrodes to inner and outer canthii:

Patient looks side to side at alternating lights

Pupil dilation and dark adaptation are not required for EOG test

EOG electrodes

EOG: Recording PhasesEOG: Recording Phases Three phases are typically recorded in EOG The pre-adapt light phase is to standardize the standing

potential, taking 1-5 min. The dark-adapt phase is to “discharge” the standing

potential, taking 10 - 20 min. The light phase is to “recharge” the standing potential,

taking 4 - 10 min. The test takes about 30 - 40 min in total. Recording of both

eyes are recommended to save time

EOG: A Normal RecordingEOG: A Normal Recording

Arden Ratio: Light / Dark > 2.0 is OK

EOG: Clinical ApplicationsEOG: Clinical Applications

Most commonly used in Best’s Disease (Best’s Vitelliform Macular Dystrophy)– ERG Normal, EOG Abnormal is CONFIRMING

diagnosis– Abnormal EOG even in patients with no symptoms of

the disorder Abnormal EOG also found in:

– Retinal pigmentary degenerations– Chorioretinal dystrophies (e.g. choroideremia)

VEP: Visual Evoked PotentialVEP: Visual Evoked Potential

Measures function of visual pathway: fovea, optic nerve, primary visual cortex

Pattern or Flash Stimulus Normally use pattern stimulus

(less variability)– Alternating grating, sinusoid, or

checkerboard pattern– Stimulus may be full field or

hemi-field Record signals at visual cortex

VEP: Electrode PlacementVEP: Electrode Placement

Recording Electrode

Ground Electrode

Reference Electrode

Computer Amp.

VEP: Recording ProcedureVEP: Recording Procedure VEP response is very small, about 20V or less, and

spontaneous brain activity and EMG may dominate the individual responses

Need to average 50-100 responses to remove noise and reveal the underlying response

Artifacts caused by head movements may distort the recording, and so the sweeps contaminated with artifact should be rejected. LKC software automatically does this.

For Pattern VEP– Patient should be properly refracted (near correction)

For Flash VEP– Must patch contralateral eye to avoid artifacts

Pattern VEP: A Normal Recording Pattern VEP: A Normal Recording

1

2

32x32 100% Contrast Checks 2 Hz

-25

-20

-15

-10

-5

0

5

10

15

20

25

0 50 100 150 200 250

Pattern VER

1: (

µV)

Oz R

milliseconds

P100 ( 100 ms)

Pattern VEP: ApplicationsPattern VEP: Applications

Optic Nerve Disorders:– Optic neuropathy (compressive, ischemic)– Optic nerve atrophy– Compressive tumors– Demyelinating disease (e.g., Multiple Sclerosis)– Toxic optic neuropathies (ethambutol, cisplatin)

Malingering, hysterical blindness Can use hemifield stimulation to distinguish pre-chiasmal

from post-chiasmal effects

Flash VEP: ApplicationsFlash VEP: Applications

Assessing visual function behind media opacities Surgical monitoring

– Intraorbital surgery with risk for optic nerve damage– Endoscopic sinus surgery

ConclusionsConclusions

• Visual Electrodiagnostic testing provides a way to measure the function of the retina and the visual pathway.

• The functional examination is at the cellular level, and the recordings can be further studied with morphological data.

• Clinical applications of visual electrophysiology are broad, and researches are being carried out for more applications.

Thank You!Thank You!