Study designSystematic review.ObjectiveTo summarise the parameters available to measure horizontal gaze, provide their values in patients and/or asymptomatic individuals, and assess their reliability.MethodsA literature search was conducted on 9/9/2023 using Medline and Embase, applying the following keywords: "horizontal gaze" or "gaze line". Articles that reported on horizontal gaze were included.ResultsTwenty-six articles published between 2015 and 2023, were included, of which 15 reported on patients, 10 reported on asymptomatic individuals, and one reported on both. The three most reported horizontal gaze parameters were McGregor's slope (n = 20 studies, asymptomatic individuals range: -8.8-10.2°), C0-C2 angle (n = 18 studies, asymptomatic individuals range: -32.0-101.5°), and chin brow vertical angle (CBVA) (n = 12 studies, asymptomatic individuals range: -5.9-12.7°). The most frequently reported correlations were between McGregor's slope and C0-C2 angle (R,-0.390-0.676