The Morphology of the Palpebral Fissure in Different Directions of Vertical Gaze

Abstract

The purpose of this study is to investigate the normative morphology of the palpebral fissure by measuring a range of biometric eye dimensions for a population of young subjects through analysis of digital images in primary gaze and two typical angles of downward vertical gaze. Palpebral fissure characteristics are clinically important in areas such as contact lens practice. High-resolution digital images were taken of 76 young subjects with a range of refractive errors in primary gaze and 20 degrees and 40 degrees downward gaze. The digital images were analyzed to ascertain a range of biometric measures of the palpebral fissure for each subject in each angle of gaze. Repeated-measures analysis of variance was used to investigate changes occurring in the palpebral fissure dimensions with vertical angle of gaze. Highly significant changes were found to occur in the horizontal and vertical palpebral fissure dimensions, the palpebral fissure angle, and the eyelid contour as a function of angle of gaze. The palpebral fissure narrows in the vertical dimension (from an average vertical palpebral aperture width for white subjects in primary gaze of 9.7+/-1.2 mm to an average width of 6.4+/-1.1 mm in 40 degrees downgaze), shortens in the horizontal dimension (from average horizontal palpebral aperture width of 27.1+/-1.5 mm in primary gaze to an average of 25.6+/-1.8 mm in 40 degrees downgaze), and becomes more "down-slanted" with increasing downward gaze. Highly significant changes to the palpebral fissure dimensions occur in downward vertical gaze. These changes are important because many visual tasks are performed in downward gaze. These findings have implications for the management of lid anomalies and for contact lens fitting and design.