Effect of luminance on the visually-evoked potential in visually-normal individuals and in mTBI/concussion

Abstract

Purpose: To assess quantitatively the effect of luminance on VEP amplitude and latency in visually-normals (VN) and patients with mild traumatic brain injury (mTBI).

Methods: VN individuals (n = 20) and those with mTBI (n = 19) participated. Those with mTBI were assessed 1–10 years post-injury (mean = 4.97 years), with the exception of one subject. Pattern VEP testing was employed using the DIOPSYS™ NOVA–TR system, with a 74 cd m⁻² baseline luminance. Luminance levels were reduced with five different neutral density (ND) filters (0.5, 1.0, 1.5, 2.0 and 2.5) and compared to the baseline response. All testing was performed under binocular-viewing conditions with full refractive correction in place.

Results: In both groups, mean VEP amplitude reduced with decrease in luminance (p < 0.05). At each luminance level, the mean VEP amplitude was significantly lower in mTBI than in the VN population (p < 0.05). In both groups, the mean VEP latency increased progressively with reduction in luminance (p < 0.05), with it being significantly higher in mTBI than in the VN population (p < 0.05).

Conclusions: High luminance levels produced an optimal VEP response in both populations. VEP amplitude was robust, whereas latency progressively increased in both groups as luminance decreased. The latency increase with decreased luminance was significantly larger in those with mTBI, thus suggesting that latency can be used to differentiate reliably between VN individuals and those with mTBI.

• Amplitude
• latency
• luminance
• magnocellular pathway
• mild traumatic brain injury (mTBI)
• objective biomarker
• visually-evoked potential
• VEP

Acknowledgments

We thank the National Eye Institute T35 Research Program for support to Vanessa Fimreite (5T35EYO20481-04), DIOPSYS Inc., (Pine Brook, NJ) for supplying the VEP system, and the Graduate Program at the SUNY College of Optometry for partial funding. We thank Dr Kevin Willeford for his critical reading of the manuscript.

Declaration of interest

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.