Parameters Used to Define Horizonal Gaze: A Systematic Review

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; P < 0.065; n = 4 studies), McGregor's slope and CBVA (R, 0.679-0.862; P < 0.0001; n = 3 studies), as well as CBVA and slope of the line of sight (R, 0.592-0.996; P < 0.001; n = 3 studies).ConclusionThe present systematic review identified 18 parameters used to measure horizontal gaze; however, there is no gold standard. Although parameters had good to excellent inter-observer reliabilities, there were large variations in measurements among asymptomatic individuals across studies, which may imply a limited clinical relevance. Therefore, there is a need for a gold standard parameter of horizontal gaze, which uses easily identifiable landmarks that are simple to measure (reliable), relates both orbital and cervical anatomical structures, and provides insight into compensatory mechanisms in deformative or degenerative conditions.