For a study, researchers aimed to audit and compare existing radiological definitions of gaze direction—chin brow vertical angle (CBVA), McGregor slope (McGS), the slope of the line of sight (SLS), orbital-internal occipital protuberance (OIOP) slope angle, and Tangent to the hard palate (THP) in a neutral, healthy, and asymptomatic cohort. The mean age was somewhere between 45 and 15.9 years, with a balanced male-to-female ratio. Their C7 SVA (–7.7mm±24.8 mm), PI (51.0o±11.4o), PI-LL (−0.9o±13.0o), and T1-slope (21.2o±9.2o). Measured horizontal gaze parameters were as follows: CBVA (1.07o±5.48o), McGS (−3.23o±5.63o), SLS (0.45o±5.34o), OIOP (5.03o±4.66o), THP (-0.17o±6.27o). CBVA correlated strongly with McGS (r=0.679,P<0.001), SLS (r=0.592, P<0.001), OIOP (r=0.697,P<0.001), and THP (r=−0.504, P<0.001). OIOP had the lowest variance amongst all factors and showed less variability than CBVA (SD 4.66 Var 21.69 vs SD 5.48 Var 30.08, P=.012). Multivariate calculation showed that the C2-7 angle was the only factor associated with OIOP values (P=0.006). OIOP was found to be the least variable and most robust radiological method for determining gaze direction. It used easily recognizable anatomical landmarks and an angular criterion, which made it advantageous both with x-rays or slot scanners.
