ULTRASTRUCTURAL AND ENZYME-HISTOCHEMICAL STUDIES ON REGIONAL DIFFERENCES WITHIN THE CILIARY MUSCLE OF DIFFERENT SPECIES

Background: The ciliary muscle in man serves two different functions, namely accommodation and regulation of aqueous outflow. It is still no t known whether both functions are combined or whether they can also b e fulfilled independently from each other. (The latter could provide t he possibility of an isolated pharmacological influence on the outflow -related function which should certainly be of use e.g. in glaucoma tr eatment). Material and methods: To investigate the presence of functio nally different muscle portions within the ciliary muscle and its rela tion to accommodation we have studied the ciliary muscle of various sp ecies showing no (rat, rabbit), moderate (cattle) and good (cat, tupai a glis) accommodative activities. For that purpose enzyme histochemica l methods were used which are normally applied for differentiation of skeletal muscle fibers into fast phasic type II-fibres and slow tonic type I-fibres. Additionally, electron microscopical studies were under taken to evaluate the ultrastructure of the muscle cells. Results: It was found that only those species showing accommodation, were characte rized by slight (cattle) or pronounced (cat, tupaia glis) differences in histochemical staining and ultrastructure of muscle cells. Characte ristically, the longitudinal portion showing structural affinity to th e aqueous outflow system, was different from the inner reticular and c ircular portions showing more relation to accommodative functions. Con clusions: These differences might indicate that two different function al systems within the ciliary muscle do exist which have been develope d during evolution of higher accommodative mechanisms in the eye.