The Lower Eyelid Movement by Inferior Oblique Muscle Action According to the Age

ABSTRACT

PURPOSE: There have been few studies on the dynamic analysis of lower eyelid movement. The inferior oblique muscle deep in the inferior orbit is well connected with the extraocular muscle by capsulopalpebral fascia and is involved in the lower eyelid movement. The purpose of this study was to determine the graphical equation of the lower eyelid contour and to quantify the dynamic movement of the lower eyelid at primary gaze and inferior oblique action gaze in normal eyes according to age, as such findings have never been reported before. METHODS: One hundred and forty subjects who had no previous eye or eyelid disease and surgery, aged from 5 to 68 years (35.75+/-30.59 years) were enrolled and divided into 7 age groups. We analyzed digital camera images to obtain the lower eyelid curvature and traveling distance of the lowest point of the lower eyelid accompanied by the action of the inferior oblique muscle. RESULTS: Graphical analysis presented the relationship of the cubic equation resembling the lower eyelid contour. The curvature of the lower eyelid at the gaze of inferior oblique muscles action became flatter than that of the primary position in all age groups. The lowest point of the lower eyelid moved significantly to the medial position and up from the primary gaze at the gaze of the inferior oblique muscles action in all age groups. There was no difference in traveling distance of the lower eyelid at each direction between sexes and age groups. CONCLUSIONS: The lower eyelid movements associated with the inferior oblique muscle are believed to be innate. We suggest that the digital image analysis of the lower eyelid contour will be useful to analyze the lower eyelid movements.