Pathomechanism of iris sphincter tear.

Traumatic iris sphincter tear has been thought to occur secondary to anteroposterior compression of the globe with defined forces lead to equatorial expansion and active pull along the corneoscleral junction and sphincter tear. However, here in this report, we elaborate the additional forces involved in the traumatic rupture of the sphincter pupillae muscle. During the anteroposterior compressive forces along the globe, the corneal deformation beyond certain limits leads to the development of sudden displacement forces within the anterior chamber. Aqueous within it which is incontinuous circulation with a posterior narrow pupillary aperture as its entrance, find the path of least resistance that is along the pupillary orifices leading to anexpulsive drive to displace the fluid through this small aperture. During this process, the horizontally oriented mechanical stretching forces appear to be the main cause ofpupillary sphincter tear.