Ultrastructural Anatomy of Normal Lacrimal Drainage System

Ultrastructural studies help understand the tissue structures, functions, and aberrations at surface, cellular, and subcellular levels [1–8]. It is carried out using scanning and transmission electron microscopy. Scanning electron microscopy (SEM) of healthy lacrimal systems has shown demonstrable anatomical junctions between the distal portion of the punctum and the proximal portion of the vertical canaliculus [1, 8]. Such anatomical junction was also noted between the lacrimal sac and nasolacrimal ducts [1, 7]. The mucosa of the canaliculus was occasionally thrown into folds, with the surface showing rugae as compared to the usual smooth architecture. These are likely to represent the valvular structures of the lacrimal system [1]. In the vicinity of the canaliculi, the orbicularis fibers were found to be very well organized in bundles with a distinct anatomy of the Horner–Duverney muscle [9]. The anatomy of the internal common opening (ICO) is distinct with demonstrable sinus of Maier, distinct anatomy of the peri-ICO depression, and canalicular lacrimal sac mucosal folds [6]. The fundus of the lacrimal sac showed very peculiar glands not found elsewhere and whose function is not yet known. The walls of the lacrimal sac and nasolacrimal ducts showed dense vascular plexus, which included wide luminal arteries, throttle veins, and large capacitance vessels. The mucosa of the lacrimal sacs showed well-defined elevations of submucosal lymphoid follicles and epithelium with dense villi and occasional cholinergic brush cells [5]. The anatomy of the opening of the nasolacrimal ducts into the inferior meatus is also distinct when examined ultrastructurally [7]. These topographic studies can enhance our anatomic–physiological understanding, which may then be translated for better clinical understanding and patient management.