Effect of aging on human rectu extraocular mucle path demontrated by magnetic reonance imaging

PURPOE: To compare normal functional anatomy of rectu extraocular mucle (EOM) and pulley in normal older human with previouly reported finding in younger ubject. DEIGN: Experimental tudy of the orbit of normal healthy older volunteer by magnetic reonance imaging (MRI). METHOD: In plane perpendicular to the orbital axi, contiguou MRI image panned the anteropoterior extent of 22 orbit in 12 older adult with an average age of 65.2 year (range, 56–74). Image were obtained in central gaze in all ubject and repeated in upraduction, infraduction, abduction, and adduction in ome ubject. Mean EOM cro-ectional area centroid were normalized to an oculocentric coordinate ytem and plotted over the length of each EOM to determine path. REULT: Compared with image obtained uing identical technique in 12 younger ubject (average age, 28.5 year, range 21–33), the horizontal rectu EOM in the 12 older ubject were ignificantly diplaced inferiorly throughout the anteropoterior extent of the orbit. The vertical rectu EOM wa poitioned identically to thoe of younger ubject. Inflection in EOM path produced by the connective tiue pulley could not be determined in mot older ubject, becaue of difficultie in maintaining extreme eccentric gaze. For one ubject who wa able to do thi, the anteropoterior location of the medial rectu pulley inferred from path inflection wa imilar to that of younger ubject. CONCLUION: The horizontal rectu EOM are diplaced inferiorly in the elderly relative to the globe center. Thi diplacement preumably reflect an inferior location of the correponding pulley, partially converting horizontal rectu EOM force to depreion. Thi may contribute to the oberved impairment of elevation in older people and predipoe them to a characteritic pattern of incomitant trabimu