Final Exam

Electrophysiology

The electrical properties of the nervous system. Clinical assessment of this via probing of the visual system always for the objective assessment of the visual pathway. Provides the ability to locate and identify sources of a visual disturbance.

Dipole

polarized electrical field created within a surrounding tissue when an electrical impulse is conducted by underlying neural tissue

Evoked potential

changes in electrical potential of cells and fluids surrounding neural tissues in response to a known stimulus. Can be measured noninvasively via electrodes placed upon the tissues. Ie) EOG, ERG, VEP

Visual stimulator

component of the electrophysiological testing apparatus that controls the image seen by the patient and simultaneously communicates with the data acquisition computer regarding when the stimulus is present.

Electrical transducers/electrodes

component of the electrophysiological testing apparatus that senses small evoked potentials made by tissues such as the scalp, skin, or ocular surface.

Physiological amplifier

component of the electrophysiological testing apparatus that functions to boost the signal as much as 10^5 times. The signal is then filtered to remove extraneous electromagnetic noise generated by the equipment and body which are irrelevant to the visual signal.

Data converter

component of the electrophysiological testing apparatus that functions to transform the analog signal at a high rate to digital information which can be analyzed by clinicians.

waveforms

Visual signals detected via electrophysiological testing can be converted into digital information displayed as _____ which can be analyzed by clinicians.

Signal Averaging

technique used to extract the visual signal from the noise producing during electrophysiological testing. It is performed by taking the sum of the responses divided by the number of the stimulus presentations. Neural noise averages out to zero, and any net average is activity due to the visual stimulus. The higher number of averages, the greater degree of noise reduction.

Latency

difference between response start time and the time that the stimulus was presented. Measured in milliseconds. Ie) increased in patients having optic neuritis in addition to a decreased waveform amplitude

Amplitude

the voltage across the peak and the trough of a waveform

Recovery time

the time is takes for the visual system to respond maximally to an additional stimulus following prior stimulation. Important for this time to occur fully, so that a complete response-recovery process is reflected by each stimulus presentation.

Steady state response

response produced when there is repetitive and rapid stimulus presentation occurring before the visual system has time to recover.

Transient response

response produced when there is stimulus presentation occurring well after the visual system has time to recover. This allows for a full response followed by a reaching of resting potential before the next stimulus is shown

Electrooculogram (EOG)

electrophysiological test which measures the large dipole formed by the RPE and cornea. The anterior pole of the eye (cornea) is positively charged, whereas the posterior pole (Bruch's membrane) is negatively charged. At rest the net charge across the canthi is therefore zero, and any eye movement away from primary gaze can elicit a charge change which can be measured via electrodes placed at the canthi.

Ganzfield stimulus

a bowl of homogenous uniform field light used in many clinical vision tests.

Light Dark ratio/Arden ratio

the ratio of the average dark trough amplitude and light peak amplitude established by EOG testing.

2:1

Normal light dark ratio is greater than or equal to...

1.8, 1.7

An abnormal light dark ratio is considered less than ____ for individuals younger than 60 years, or less than _____ for individuals greater than 60 years

Best's Disease

a progressive, autosomal dominant disease of the central retina where outer segments of retinal photoreceptors are phagocytized. This produces an accumulation of lipofuscin in the retina. ERG will remain normal, but EOG testing will be affected.

Lipofuscin

metabolic product produced by the phagocytosis of photoreceptor outer segments which accumulates in the retina due to Best's disease.

Best's Vitelliform dystrophy

best's disease with an onset of 8-11 years. Occurs in a series of stages resulting in a series of stages that result in reduced VA and extinguished EOG.

Multifocal Best's disease

best's disease with an onset of 30-40 years. Has a good prognosis with minimal VA loss. Carriers will have a reduced, but not extinguished EOG.

Adult onset Best's disease

best's disease with an onset of 30-40 years. Has a good prognosis with minimal VA loss. Will have normal to reduced EOG.

Hydroxychloroquine

drug used in the treatment of rheumatoid arthritis that can accumulate in and damage the retina which can be revealed via EOG testing.

Reduced night vision

an early symptoms which may be diagnostic for toxic retinopathy caused by hydroxychloroquine.

Bull's eye maculopathy

a characteristic sign of late toxic retinopathy caused by hydroxychloroquine. May be accompanied by paracentral scotomas.

Ocular siderosis

iron foreign body causing toxicity to ocular tissues. May show a reduced EOG before affecting flash ERG testing.

Chalcosis

copper foreign body causing toxicity to ocular tissues. May show a reduced EOG before affecting flash ERG testing.

6.5

A rod intercept of greater than _____ minutes is abnormal. Commonly seen in patients having toxic retinopathy due to hydroxychloroquine use.