title: Dynamic magnetic resonance imaging of the levator palpebrae superioris muscle.
abstract: The relationship between upper lid elevation (h) and shortening (s) of the levator palpebrae superioris muscle (LPS) has an influence on the dose-response relationship in ptosis surgery. In order to investigate the relationship between upper lid elevation and shortening of the LPS, parasagittal T1-weighted MR images of the orbit were obtained in healthy subjects with the eye in down- and upgaze. The position of the upper lid margin and the length of the LPS were measured in the images in down- and upgaze and the amount of h and s was determined. For a mean (+/- SD) vertical upper lid elevation of 15 +/- 1 mm, the mean (+/- SD) shortening of the LPS muscle was 21 +/- 3 mm (n = 4). The mean ratio of his was calculated to be 1:1.4, which means that the levator muscle must contract by 1.4 cm in order to achieve a lid elevation of 1 cm. Therefore, the force of the LPS which is necessary to lift the upper eyelid can be smaller than the lid-closing force. This strongly suggests a physiological mechanism which reduces the muscle force necessary for lifting the upper eyelid.
authors.affiliation: Orbital Center, Academic Medical Center, Amsterdam, The Netherlands.
authors.forename: A
authors.initials: A
authors.lastname: Ettl
authors.forename: A
authors.initials: A
authors.lastname: Daxer
authors.forename: S
authors.initials: S
authors.lastname: Priglinger
authors.forename: J
authors.initials: J
authors.lastname: Kramer
authors.forename: L
authors.initials: L
authors.lastname: Koornneef
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D001763:Blepharoptosis / Q000175:diagnosis / Q000503:physiopathology / Q000601:surgery; D005143:Eyelids / Q000033:anatomy & histology / Q000502:physiology; D006801:Humans; D008279:Magnetic Resonance Imaging; D009119:Muscle Contraction; D009801:Oculomotor Muscles / Q000033:anatomy & histology* / Q000502:physiology; D012016:Reference Values