Clinical Tests

Reference Guide to Visual Function Tests

Diagnosys offers four broad categories of visual function tests—electrophysiology, psychophysical, objective acuity, and pupillometry. These four categories complement one another, providing a complete picture of a person’s visual performance. At Diagnosys, our experts have extensive experience not only with all these tests but also with customizing them to meet the needs of the clinician.



Electroretinograms (ERG) are an assessment of retinal function done with light stimuli and electrodes placed on or near the eye. ERGs are useful for monitoring disease progression as well as safety and efficacy of treatments. Diagnostically, ERG may also differentiate between progressive and stationary disorders.

Full-Field ERG

A test that illuminates the entire visual field with a flash or flicker of light, the ffERG tests the full field global retinal response. The standard ISCEV 5-step test includes a dark and light adapted section to separately measure rod from cone system function. Biomarker timing and amplitudes are used diagnostically for several Inherited Retinal Diseases.

Diagnosys Stimulators: ColorDome, ColorFlash, ColorBurst.
Related Condition: Diabetic Retinopathy

Multifocal ERG

A test of local retinal function that quasi-simultaneously records local ERG responses, typically across a 40 to 60 degree field of view. Clinically the standard stimulus is a black and white pattern, with either a 61 or 103 hexagons. Other tests include a 5-ring stimuli and a 241 hexagon pattern to provide the highest resolution map of retinal function. Uses of the mfERG test include distinguishing between maculopathy and general retinopathies, screening for Plaquenil toxicity and measuring other localized retinal dysfunctions2.

Diagnosys Stimulators: LCD Monitor
Related Conditions: Macular Degeneration, Toxicity
Further Reading: Multifocal ERG (mfERG), ISCEV Guide

Pattern ERG

Pattern ERG tests primarily measure ganglion cell function. The stimulus is an alternating black and white checkerboard pattern of constant mean luminance. The test typically measures the P50 and N95 biomarkers whose reduction or delays are indicators for glaucoma, macular and other dysfunctions.

Diagnosys Stimulators: Envoy
Related Condition: Glaucoma
Further Reading: pERG

Photopic Negative Response

An ERG test utilizing red flashes on a blue background to maximize the retinal ganglion cell response known as the PhNR. Commonly used for patients at risk for glaucoma.

Diagnosys Stimulators: ColorDome, ColorFlash, ColorBurst
Related Condition: Glaucoma
Further Reading: PhNR



Visually Evoked Potentials (VEP) utilize occipital zone electrodes to record signals measured at the visual cortex to determine visual pathway integrity. VEPs that utilize flash or pattern stimuli may be used.

Stepwise Sweep VEP

A method for objectively assessing visual acuity. Sweep VEP utilizes a black & white, low contrast checkerboard pattern onset method to stimulate a fixating patient. A Laplace transform and Fourier analysis is performed in automatically estimating visual acuity. Tests are available for normal, low, and very low vision patients and can be useful for those with unexplained, psychogenic, or non-organic vision loss.

Diagnosys Stimulators: LCD Monitor, Sweep VEP Add-on
Further Reading: Sweep VEP (ssVEP)

Chiasmal Coefficient

A Chiasmal Calculator is a tool used to calculate optic nerve misrouting using 3-channel flash or pattern VEP. It may be used as a diagnostic tool for albinism and other misrouting disorders; this method is suitable for both children and adults.

Diagnosys Stimulators: LCD Monitor, ColorDome
Related Condition: Albinism
Further Reading: Chiasmal Coefficient Calculator

Pattern VEP

A pattern VEP presents a checkerboard pattern to central vision. The standard pattern reversal protocol is used for most patients; the pattern onset protocol is more effective for patients with nystagmus. Standard VEP protocols include 1- and 3-channel recordings as well as full and hemi field stimuli. The timing and amplitude of the P100 biomarker is useful for investigating optic nerve disease and post-retinal visual pathway dysfunction.

Diagnosys Stimulators: LCD Monitor
Related Condition: Neurological
Further Reading: Visually Evoked Potentials (VEP)

Flash VEP

A flash VEP presents a series of flashes that stimulate the entire visual field. This test is primarily used as an assessment of visual pathway integrity in children and those with media opacities or ocular trauma.

Diagnosys Stimulators: ColorDome, ColorFlash, ColorBurst.
Related Condition: Neurological
Further Reading: Visually Evoked Potentials (VEP)



The clinical electro-oculogram (EOG) is an electrophysiological test of the outer retina and retinal pigment epithelium (RPE) in which changes in the electrical potential across the RPE are recorded. The test utilizes a single red light which alternates from left to right; first in a dark adapted and then in light adapted conditions. Patients follow the light in smooth saccadic motions as electrodes on either side of the eye measure the voltage change. The Arden Ratio, which is the light peak-dark trough ratio, is calculated at the end of the test.

Diagnosys Stimulators: ColorDome
Related Condition: Bestrophinopathies
Further Reading: EOG



Electrically Evoked Responses (EER) detect cell function of the inner retina and visual pathway. A small electrical current is transmitted to the eye through a corneal electrode while electrodes placed on the visual cortex record the evoked response. EER evaluates the visual pathway from bipolar cells to visual cortex, in the absence of functioning photoreceptors. The test can be useful for many retinal diseases which have severely degraded or eliminated photoreceptor function, such as Leber Congenital Amaurosis. Not currently available to US market.

Diagnosys Stimulators: EER Module
Related Conditions: Retinitis Pigmentosa and other Inherited Retinal Diseases, Traumatized eyes with possible retinal detachment.


Dark Adaptometry

A test to measure the dark adaptation of a patient, both the cone/rod thresholds and dark adapting dynamics. Patients may be tested with red, green, blue, or white light and are asked to answer “YES” upon seeing the stimulus. Variations of the full DA protocol include faster tests to determine solely the rod threshold or measure the rhodopsin regeneration rate. The test is useful for early detection of macular degeneration and enhanced characterization of patient’s low light visual capabilities.

Diagnosys Stimulators: ColorDome, DA Module Add-on
Related Condition: Macular Degeneration


Full Field Stimulus Threshold

FST measures the sensitivity of the visual field by testing for the lowest luminance flash which elicits a visual sensation perceived by the patient. The test may be done in dark or light adapted conditions. During the test patients are presented with algorithmically derived light intensities to which they must answer YES or NO in response to whether they saw the stimulus. The test provides a quantified measure of the patient’s light perception threshold. DiagnosysFST® features quality metrics to simplify the interpretation of data.

Diagnosys Stimulators: ColorDome, ColorFlash, FST Module Add-on
Further Reading: FST Test

sweep vep

Sweep VEP

Sweep VEP objectively assesses visual acuity. The method utilizes a black & white, low contrast checkerboard pattern onset method to stimulate a fixating patient. A Laplace transform and Fourier analysis is performed in automatically estimating visual acuity. Tests are available for normal, low, and very low vision patients and can be useful for those with unexplained, psychogenic, or non-organic vision loss.

Diagnosys Stimulators: LCD Monitor, Sweep VEP Add-on

sweep vep


Pupillometry measures reflexive pupillary response to light stimuli. This test can measure pupil area or diameter and may use any combination of red, green, blue, or white light as a flash stimulus. Background lighting may be any of those color combinations or dark.

Diagnosys Stimulators: ColorDome, Pupillometry module Add-on

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