Scanning Electron Microscopic Features of the Canalicular Entrance Into the Lacrimal Sac

Detailed anatomical features of the common canalicular opening into the lacrimal sac can help our understanding of the focal anatomy and tear rheology. Purpose: The aim of this study was to examine the ultrastructural features of the canalicular entrance into the lacrimal sac. Methods: Ten openings of the common canaliculus into the lacrimal sac from 10 lacrimal sacs obtained during a dacryocystectomy were studied. Each of the openings were completely excised with 3-4 mm margins on all sides and transported to the laboratory in 2.5% glutaraldehyde. The analysis was performed using the standard protocols of scanning electron microscopy (SEM). The openings, their edges, canalicular lacrimal sac-mucosal folds, and internal surfaces were studied. Results: Of the 10 common canalicular openings studied, the upper and lower canaliculi opened into a common canaliculus in all the cases. The terminal portion of the 2 canaliculi had a common wall, which appeared like a septum, just proximal to the beginning of the dilated common canalicular portion. In 60% (6/10) of the cases, a diverticular or a type III sinus of Maier (SOM) was noted. The surface of this diverticulum was smooth and lined by stratified columnar epithelium, reflecting its lacrimal sac origins. Interestingly, the junction of the epithelial change from stratified squamous to columnar could be appreciated clearly in 80% (8/10) of the cases and was mostly located just within from the edge of the internal common opening (ICO). The canalicular lacrimal sac-mucosal folds could be appreciated in 70% (7/10) samples, being very defined and prominent in 30% (3/10). Conclusions: The common merged wall of the 2 canaliculus is the most proximal and prominent structure noted on an end-on view of the ICO. Diverticular variant of the sinus of Maier is common. The junction of the epithelial change from stratified squamous to columnar is appreciated just within the edge of the ICO.