The mechanism of ciliary muscle function

The changes of the surface arc of the ciliary muscle during contraction were modeled to under-stand its mechanism of action. From the reported measured histological configurational changes which occur in the primate ciliary muscle during pharmacologically induced contraction, the deformation of the surface arc of the muscle was evaluated using the concept of equidistribution and a force diagram developed from the known muscular fiber orientation. During ciliary muscle contraction, through the action of the radial and longitudinal fibers, the anterior portion of the ciliary muscle curls towards the sclera. The posterior portion of the ciliary muscle moves forward, primarily due to the longitudinal fibers. The circular fibers are responsible for ensuring that the force applied to the equatorial zonules remains in the equatorial plane. Contraction of the ciliary muscle produces simultaneously increased tension on the equatorial zonules and relaxation of the anterior and posterior zonules