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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
I have used Diagnosys electrophysiology systems for clinical testing and research for nearly fifteen years. The systems are reliable, easy to use and protocols readily modified to answer research questions. The few times I have had problems with the equipment, Diagnosys has quickly responded and fixed the problem.
Diagnosys LLC not only provides high quality testing equipment, but also provides excellent customer support services. All employees are knowledgeable in the field of visual electrophysiology and are able to help with any questions or issues you may have.
As a clinical neurophysiologist in a busy pediatric clinic, I wholeheartedly believe that the equipment made available to us by Diagnosys LLC allows for the testing necessary to aid in clinical diagnostics and research. I have always felt that this family run company has been by my side each and every step of the way, despite being located in another country.
Dr. Allison Dorfman
Celeris is the Luxury Vehicle of Electrophysiology! I love Celeris for the vision science field because it grants all investigators access to a wide variety of electrophysiological tests without requiring in depth expertise of the theory of electrophysiology. It's wonderfully simple and easy to operate.
Barbara A. MysonaPhD