Histochemical studies on the inferior oblique muscle of Siamese cats and domestic cats with unilateral lid suture

Abstract

Eye muscles of Siamese cats and monocularly lid sutured domestic cats have been shown to contract slower and fatigue quicker than eye muscles of normal domestic cats. The structural correlates to these functional differences were explored with histochemical techniques in the same muscles that were studied physiologically. Sections were stained for myosine ATPase and succinic dehydrogenese (SDH). The muscles of Siamese cats were smaller in cross-sectional area than muscles of ordinary cats. The proportions of type I, and type II and II C fibers were the same in all animals. In Siamese cats fibers of all types, and in domestic lid sutured animals type II fibers were smaller than corresponding types in normal cats. No differences could be detected between animals with respect to SDH staining properties. The capillary density per fiber was significantly lower in lid sutured domestic cats and Siamese cats than in normal cats. These changes in muscle and fiber area, and in capillary density are probably the morphological correlates to the observed functional differences. It has been suggested that they are related to deficiencies in visual function, particularly in binocular vision; they might represent muscular adaptation to reduced demands for fusional vergence movements in Siamese and lid sutured domestic cats, and for saccadic activity in Siamese cats.