icVEP™: Isolated-check Visual Evoked Potential

EvokeDx uniquely features icVEP, a proprietary test strategy based upon studies designed to emphasize contributions to the VEP selectively from the ON or OFF subdivisions of the magnocellular neural pathways¹.


icVEP Bright & Dark Check Patterns

Contrast / luminance of non-contiguous checks varies sinusoidally rapidly in time such that the pattern smoothly appears and then disappears. The low contrast, bright-check pattern modulated at high frequency, is thought to emphasize the M-ON pathway.
icVEP tests are designed to assess low contrast processing in the visual system, which are deficient in various disorders, including glaucoma [5]. In a multi-site, NIH-funded study, the icVEP strategy demonstrated high classification accuracy for early-stage glaucoma, Phase I  [6] (A’=94%), Phase II [7] (A’=89.2%).
Sweep versions of this test, either with steps of increasing contrast of bright checks or increasing contrast of dark checks characterize the range of low contrast vision response affected, with the final steps also including a high contrast response (thought to involve the Parvocellular pathway).
This contrast-sweep icVEP technique was applied to a study of schizophrenia and autism which discovered selective deficits in visual processing. Selective low-contrast deficits were found using this technique in a study of patients with retinitis pigmentosa as well[8].

VEP: Visual Evoked Potential

EvokeDx includes a spatial frequency sweep VEP, ISCEV standard transient VEPs (high and low contrast reversing checkerboard) and three novel VEP tests unique to EvokeDx; steady state Windmill Dartboard and Partial Windmill Dartboard, and a Transient Uniform Field test useful for patients with dense cataracts/low vision.

ERG: Electroretinogram

Electroretinography or electroretinograms (ERG) is an important clinical tool that provides an objective quantitative measure of retinal function. ERGs elicited by patterned stimuli (PERGs) reflect the activity of the inner retina (primarily retinal ganglion cells) whereas ERGs resultant from luminance modulation of a uniform field taps activity of the outer retina (primarily ON bipolar cells).

It follows that ERG tests assess various types of visual function responses prior to modification of neurons in the brain. ERGEvokeDx features a dual channel amplifier and a five electrode ERG cable that enables binocular ERG recording, cutting ERG test time in half when compared to single channel, three electrode systems.


Konan’s EvokeDx is engineered to utilize industry-standard EEG electrodes with a ubiquitous snap connector.  Expensive, proprietary lid-electrodes are not necessary or required. With EvokeDx you have great choices:  low-cost, pre-jelled electrodes for ERG, and two-part scalp electrodes for VEP. Scalp electrodes can be easily applied, and securely held in place with our T-band and electrode keepers. Your techs will love the improved ease of application and reliability of secure apposition of electrodes to the scalp.

[1] Zemon, V., & Gordon, J. (2006). Luminance-contrast mechanisms in humans: visual evoked potentials and a nonlinear model. Vision research, 46(24), 4163-4180.
[2] Zemon, V., Eisner, W., Gordon, J., Grose-Fifer, J., Tenedios, F., & Shoup, H. (1995). Contrast-dependent responses in the human visual system: childhood through adulthood. International Journal of Neuroscience, 80(1-4), 181-201.
[3] Dacey, D. M., & Petersen, M. R. (1992). Dendritic field size and morphology of midget and parasol ganglion cells of the human retina. Proceedings of the National Academy of sciences, 89(20), 9666-9670.
[4] Yeh, C. I., Xing, D., & Shapley, R. M. (2009). “Black” responses dominate macaque primary visual cortex v1. The Journal of Neuroscience, 29(38), 11753-11760.
[5] Greenstein, V. C., Seliger, S., Zemon, V., & Ritch, R. (1998). Visual evoked potential assessment of the effects of glaucoma on visual subsystems. Vision research, 38(12), 1901-1911.
[6] Zemon, V., Tsai, J. C., Forbes, M., Al-Aswad, L. A., Chen, C. M., Gordon, J., … & Jindra, L. F. (2008). Novel electrophysiological instrument for rapid and objective assessment of magnocellular deficits associated with glaucoma. Documenta ophthalmologica, 117(3), 233-243.
[7] Nayak, N., Hu, G., Lin, J., Tsai, J., (2011). Utility of the Isolated-Check Visual Evoked Potential Technique as a Glaucoma Monitoring Device. ARVO, #5480.
[8] Alexander, K. R., Rajagopalan, A. S., Seiple, W., Zemon, V. M., & Fishman, G. A. (2005). Contrast response properties of magnocellular and parvocellular pathways in retinitis pigmentosa assessed by the visual evoked potential. Investigative Ophthalmology and Visual Science, 46(8), 2967-2973.