The Type and Content of Collagen Fibers of the Levator Aponeurosis in Patients With Simple Congenital Blepharoptosis.

BACKGROUND: The pathogenesis of congenital blepharoptosis remains controversial and most of the studies focused on the histologic changes of the levator muscle. However, thickening of the aponeurosis was reported in congenital blepharoptosis. And the thickness of the levator aponeurosis was found to be correlated with the levator function in congenital dysmyogenic blepharoptosis. PURPOSE: The authors conducted this research to investigate the histological changes of the levator aponeurosis of simple congenital blepharoptosis patients. PATIENTS AND METHODS: The authors analyzed 12 levator aponeurosis from ptosis patients and 21 levator aponeurosis from the cadaver specimens without relative medical history. The specimens were stained with hematoxylin and eosin as well as Sirius red. The sections were examined under light-microscopy. The content and type of collagen fibers were examined with the photos taken of the sections stained with Sirius red under polarized light-microscopy. RESULTS: The content and proportion of type I collagen increased significantly in the patient group compared with the cadaver group. The proportion of type I collagen was 97.5% in the patient group, while it was 51.5% in the cadaver group. However, no correlation was found either between the levator strength, degree of ptosis and the proportion of type I collagen in the patient group or between age, gender and proportion of type I collagen in the cadaver group. CONCLUSIONS: To our knowledge, this is the first time this phenomenon was discovered. The increase of type I collagen in the levator aponeurosis of the simple congenital blepharoptosis patients may imply the increased stiffness and undermined ability of transmitting forces, dissipate energy and prevent mechanical failure in the levator aponeurosis.

Mechanical properties, physiological behavior, and function of aponeurosis and tendon.

During human movement, the muscle and tendinous structures interact as a mechanical system in which forces are generated and transmitted to the bone and energy is stored and released to optimize function and economy of movement and/or to reduce risk of injury. The present review addresses certain aspects of how the anatomical design and mechanical and material properties of the force-transmitting tissues contribute to the function of the muscle-tendon unit and thus overall human function. The force-bearing tissues are examined from a structural macroscopic point of view down to the nanoscale level of the collagen fibril. In recent years, the understanding of in vivo mechanical function of the force-bearing tissues has increased, and it has become clear that these tissues adapt to loading and unloading and furthermore that force transmission mechanics is more complex than previously thought. Future investigations of the force-transmitting tissues in three dimensions will enable a greater understanding of the complex functional interplay between muscle and tendon, with relevance for performance, injury mechanisms, and rehabilitation strategies.