Maintaining a horizontal gaze is crucial for humans to interact with their surroundings and perform daily tasks. This gaze is evaluated using horizontal gaze parameters, including the chin–brow vertical angle (CBVA), McGregor slope (MGS), and slope of the line of sight (SLS). However, the normative ranges for SLS and CBVA, as well as their associations with cervical sagittal parameters, remain unclear. This study aimed to determine the normal ranges of horizontal gaze parameters based on their relationships with cervical sagittal parameters.

The normal ranges of horizontal gaze parameters can be established by analyzing their correlations with cervical sagittal parameters.

In 50 asymptomatic individuals, horizontal gaze parameters and cervical sagittal parameters were assessed using standing lateral cervical radiographs that included the skull. Pearson’s correlation coefficient was used to analyze the relationships between these parameters. Additionally, predictive formulas were derived through linear regression analysis of significantly correlated parameters to define the normative ranges of horizontal gaze parameters.

Horizontal gaze parameters demonstrated significant correlations with the C2 slope (C2S) (T1 slope [T1S] minus cervical lordosis [CL]) and the C2-7 sagittal vertical axis (C2-7 SVA). They also showed significant but relatively weaker correlations with CL (p < 0.05). Based on the normal CL range (−8° to –29.5°), the estimated ranges for CBVA, MGS, and SLS were −10.8° to 7.83°, −6° to 14°, and −15.5° to 8°, respectively.

The significant correlations between horizontal gaze parameters and C2S as well as C2-7 SVA allow for the identification of kyphotic thresholds. Furthermore, kyphotic and lordotic thresholds can be determined based on their relationship with CL. However, larger studies are necessary to refine predictive formulas further.

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