Using continuous visual stimulus tracking for detecting visual function loss due to acquired brain injury

Acquired brain injury (ABI) may cause homonymous visual field (VF) defects. Standard automated perimetry (SAP) is the gold standard for VF assessment, but it can be challenging in ABI. Continuous visual stimulus tracking (SONDA; Standardised Oculomotor and Neurological Disorders Assessment) simplifies the perimetric task to following a moving stimulus on a screen. We investigated whether tracking performance (agreement between gaze and stimulus position) measured with a SONDA-based eye movement perimetry technique (SONDA-EMP) (1) can detect visual function loss in patients with homonymous VF defects, (2) can quantify visual function loss (in terms of SAP Mean Sensitivity [MS]) and (3) shows a learning effect.

Tracking performance was evaluated in 16 cases with unilateral ABI (median [IQR] age 66 [62-68] years; SAP MS 19 [15-21] dB; 8/8 with left-/right-sided VF defect) and compared to previously collected data of 36 controls (age 70 [67-72] years). All participants monocularly tracked a moving stimulus (Goldmann size III) at three Weber contrasts (40%, 160% and 640%), while their eye movements were recorded.

ABI significantly decreased tracking performance (p < 0.0001) compared to controls at all contrasts, independently of VF defect side (p = 0.53). Performance improved from 40% to 160% contrast (p < 0.0001), but not from 160% to 640% (p = 0.53). SAP MS correlated moderately to strongly with tracking performance (r = 0.46 [p = 0.07], 0.73 [p = 0.01], 0.67 [p = 0.004], for 40%, 160% and 640% contrast, respectively). Retesting showed no significant learning effect.

SONDA-EMP can detect visual function loss from ABI. The reduction in tracking performance depends on the amount of VF loss.