Validation of a Visual Midline Gauge: A Cross-Sectional Study

Abstract

BackgroundThis study standardized the parameters of a novel visual midline gauge and presents normative data, which can be used by optometrists in the assessment of visual midline.MethodsNinety-three participants from three age groups (18 to 44, 45 to 64, and > 65 years) without history of significant neurological or ocular problems were recruited in Waterloo, Canada and Hong Kong. In experiment 1, the perceived horizontal and vertical visual midline was measured using the gauge for 2 speeds and 2 repositioning methods. In experiment 2, the perceived midline was measured for three different distances (25, 50 and 100 cm) using a target speed and repositioning method chosen from the first experiment results. Since there was no significant difference between the two sites in any of the measures, data were combined for analysis.ResultsFor experiment 1, linear mixed models showed no effect of age, speed or repositioning method and no interaction (p>0.05) for the perceived midline position (p>0.05). In experiment 2, there was no significant effect of age or distance and no interaction effects on the perceived horizontal and vertical visual midline position using the chosen speed and method (2.3 degrees per second, adjustment method). Normative data (mean and 95% ranges of the perceived visual midline for control participants) was tabulated. The measurements were found to be repeatable. A few participants were found to have significant midline shifts.ConclusionThis study shows that the measurement of midline is tolerant of differences of target speed, testing method, test distance, and age group of the participants and that the measurements using the visual midline gauge are repeatable. It is possible for even individuals without a history of neurological or ocular disorders to have significant shifts in their perceived visual midline.