Spatial contrast sensitivity function of patients with mild traumatic brain injury

Abstract

Purpose : To determine how the spatial contrast sensitivity function (sCSF) is altered in patients with mild traumatic brain injury (mTBI).

Methods : sCSF was measured in 10 patients with a diagnosis of mTBI (22-53 years age) and 17 control subjects (22-71 years age) using a Metropsis visual function assessment system (Cambridge Research Systems Ltd.) employing the Psykinematix software. The stimulus consisted of a 3 degree circular patch and sinusoidal gratings (0.5–32 cpd) combined with a circular Gaussian envelope (sigma=0.5 and AR=1). The mean luminance was 87 cd/m² and stimulus duration was 500ms. A two alternate forced choice test paradigm (90/180 degree orientation) was used with thresholds determined by the average of the last 4 response reversals. The data was fitted with the equation y=(a+bx)*(e^-cx). The CSF parameters of S_max: peak contrast sensitivity, F_max: spatial frequency with peak contrast sensitivity, b: bandwidth at half the peak contrast sensitivity and F_c: high-spatial frequency cutoff were derived from the fits and compared between mTBI patients and age matched controls.

Results : Significant reduction with age was observed for the control subject group for S_max (r²=0.49, slope=-0.012, p=0.001), F_max (r²=0.27, slope=-0.032, p=0.018), and F_c (r²=0.36, slope=-0.314, p=0.006). None of the parameters were significantly altered by age in the mTBI patient group. sCSF parameters of mTBI patients were compared to a subset of control subjects in the same age range (Mean age of 36+11.6 years for mTBI and 38+11.4 years for controls, p=0.71 for age difference between groups). S_max was the only CSF parameter that was significantly different (p=0.02) between mTBI patients (0.69+0.29) and age-matched control subjects (0.96+0.24). Snellen visual acuity was not significantly different between the mTBI patients and age-matched controls and the F_c of the two groups were not significantly different from the Snellen visual acuity of the respective groups converted to cpd.

Conclusions : sCSF is likely to be reduced in mTBI patients when Snellen visual acuity is normal. CSF testing at the peak spatial frequency is likely to be most sensitive in detecting CSF deficits in mTBI patients. This finding may assist in the evaluation of vision in mTBI.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.