Anatomy and Histology of the Lacrimal Fluid Drainage System

Okajimas Folia Anat. Jpn., 77(5): 155-160, December . 2000

Rieko KOMINAMI, Satoru YASUTAKA, Yutaka TANIGUCHI and Harumichi SHINOHARA

Department of Anatomy II, Kanazawa Medical University , Uchinada, Ishikawa 920-0265, Japan

-Received for Publication, August 1, 2000-

Key Words: Lacrimal fluid, Canaliculus, Common canaliculus, Lacrimal sac

Summary: Five human specimens of the lacrimal canaliculus and sac were examined by light and scanning electron microsopy. The superior and inferior lacrimal canaliculi are lined with stratified squamous epithelium that is non- keratinized and non-mucin-producing. The common canaliculus is also lined with stratified squamous epithelium, but its lumen is much narrower than the lumen of the superior and inferior canaliculi. The common canaliculus opens into an ample space called the vestibule, where the epithelium changes to high pseudostratified columnar and then low pseudostratified columnar. The vestibule continues to the infundibulum of the lacrimal sac. The infundibulum is formed by several epithelial folds that radiate from the vestibular opening to the lacrimal sac. The vestibule and infundibulum are consistent transitional structures from the common canaliculus to the lacrimal sac. The connective tissue of the lamina propria from the common canaliculus to the lacrimal sac has two histological characteristics: numerous free cell aggregates (= lymphoid structure) and numerous venules and capillaries (= cavernous structure).

Lacrimal fluid enters the punctum, passes Materials and Methods through the lacrimal canaliculus and sac, and finally drains into the nasal cavity through the nasolacri- Five human specimens of the lacrimal canaliculi mal duct. This duct system has been studied in and sac were obtained from two males and three terms of gross anatomy (Jones, 1961) and histology females, 68 to 92 years of age. One of the speci- (Fernandez-Valencia and Pellico, 1990; Paulsen et mens was embedded in paraffin, serially sectioned al., 1998), and it has also been studied in terms of in the sagittal planes, and stained with Meyer's tear drainage function (Doane, 1981; Hurwitz, hematoxylin and eosin. The remaining four speci- 1996) and immunologic self-defense (Paulsen et al., mens were dissected grossly or under a dissecting 1998). Earlier publications, however, are inade- microscope, and samples of the lacrimal canaliculus quate for understanding the morphology of the and sac were collected for semithin sections and lacrimal drainage system. For example , it is known scanning electron microscopy (SEM). The speci- that the canaliculus is lined by stratified squamous mens for semithin sections were fixed in 2.5% glu- epthelium and the lacrimal sac by pseudostratified taraldehyde in 0.1 M phosphate buffer solution epithelium (Ross and Romrell, 1985), but where (PBS) at pH 7.4 for an hour, dehydrated in a grade and how the former changes into the latter is series of ethanol, embedded in epoxy resin, and unknown. sliced 0.5 gm thick. The sections were then stained In the present study, we dissected the human with toluidine blue. The specimens for SEM were adult lacrimal canaliculus, lacrimal sac, and part of fixed in 2.5% glutaraldehyde in 0.1 M phosphate- the nasolacrimal duct. We also prepared histo- buffered saline (PBS) at pH 7.4 for an hour, post- logical sections and specimens for scanning electron fixed in 1% osmium tetroxide in PBS, dehydrated microscopy and discovered the presence of junc- in ethanol, critical-point-dried, gold-coated, and tional structures between the common canaliculus viewed with a scanning electron microscope (JSM- and lacrimal sac. 840, JEOL). 156 R. Kominamiet al.

Results was varied in diameter from 100 to 250 micro- meters, possibly due to the planes of sectioning. The distance from the base of the inferior lac- The superior and inferior canaliculi did not join as rimal papilla to the lacrimal sac ranged from 12 to equal partners, instead the superior canaliculus 16 mm in these adult specimens. The superior lac- emptied into the inferior canaliculus like a small rimal punctum was situated approximately 3 mm branch emptying into the main stream. Conse- medial to the inferior lacrimal punctum. The lac- quently, the common canaliculus was more of a rimal canaliculus is divided into two portions: ver- continuation of the inferior canaliculus. The com- tical and horizontal. The vertical portion was about mon canaliculus was usually lined with stratified 2 mm in length and contained a few longitudinal squamous epithelium, but occasionally with pseu- folds (Fig. 1). Horner's muscle surrounded the ver- dostratified columnar epithelium (Fig. 5). Its lumen tical portion. Although the orientation of the indi- was less than 100 p,m in diameter, and narrower vidual muscle fibers were unclear, some muscle than the canalicular lumen. The common canal- fibers circled around the vertical portion, while iculus continued to the vestibule, whose lumen was others coursed parallel to it (Figs. 1 and 2). The several times the diameter of the common canal- muscle also surrounded the entire circumference of icular lumen. It was initially lined with high pseudo- the horizontal portion near the vertical portion. stratified columnar epithelium but converted to low Horner's muscle covered only the anterior surface pseudostratified columnar epithelium (Figs. 4A and in the horizontal portion near the common canal- 4B). The vestibule continued to the infundibulum iculus. The common canaliculus was approximately of the lacrimal sac. The lining of the lacrimal sac is 3 mm long when measured from the lacrimal sac in low pseudostratified columnar epithelium (Fig. 6), its thick connective tissue sheath. The lacrimal sac and the cells were approximately 30 gm in height. formed a small flat cistern medio-lateral diameter The basement membrane was thick for most part. of about 1 mm and a large antero-posterior diame- There were numerous mucin-producing cells in ter of about 2.5 mm. When the lacrimal sac was the lacrimal sac epithelium, and they often formed viewed from inside, the lateral wall was seen to clusters of secretory cells. Brown-pigment cells, contain a star-shaped slit approximately 2 mm from probably melanocytes, were also numerous in the the cranial end of the sac, and several epithelial lacrimal sac epithelium (Fig. 4A, arrowheads) and folds radiated from the center of the star. The slit subepithelial connective tissue. corresponds to the infundibulum of the lacrimal sac There were two distinctive features in the sub- (see the next paragraph). epithelial connective tissue from the common The canaliculus near the lacrimal punctum was canaliculus to the lacrimal sac: the presence of free lined with non-keratinized and non-mucin-produc- cell aggregates and numerous venules and capil- ing stratified squamous epithelium. It was clearly laries (Figs. 4A and 5). The cell aggregates were discriminated from the anteriorly-situated kerati- predominantly composed of lymphocytes, but mast nized epithelium of the palpebral epidermis (Figs. cells and plasma cells were common. Several capil- 3A and 3B) and from the posteriorly-situated laries 10-20 gm in diameter were usually present in mucin-producing epithelium of the conjunctiva the aggregates, and the area had appearance of (Figs. 3A and 3C). The canalicular epithelium was lymphoid tissue. Capillaries were not entirely ab- 75-150 gm in thickness and consisted of a few layers sent in the superior and inferior canaliculi, but were of squamous cells, several layers of polyhedral cells, far less in number than in the common canaliculus and a layer of basal cells. The canalicular lumen and lacrimal sac. Numerous small veins and capil-

Explanation of Figures

Plate I

Fig. 1. Scanning electron microscopy view of the vertical portion of the inferior canaliculus. The lumen (L) is surrounded by the stratified squamous epithelium (SE). Cut-ends of circular muscle bundles are visible (arrows) between the longitudinal muscle bundles (M) and connective tissue (CT) of the lamina propria. Fig. 2. Semithin section stained with toluidine blue. Fig. 3. Paraffin section through the inferior lacrimal punctum. The epithelium of the canaliculus (C) is nonkeratinized and non- mucin-producing. Note the clear transition from the keratinized palpebral epidermis (arrowheads) and from the mucin- producing epithelium of the conjunctiva (arrows). Squares B and C correspond to insets. The arrows in the insets indicate the borders of the epithelia. PA; Palpebral aperture. Lacrimal Canaliculus and sac 157

Plate I 158 R. Kominamiet al.

lanes in the common canaliculus and lacrimal sac might cause collapse of the common canaliculus at formed a cavernous structure. Some of the capil- the kink. Thus, reflux from the lacrimal sac toward lanes were adjacent to the basement membrane. the common canaliculus is blocked as though there The common canaliculus was consistently accom- were a valve at the junction. According to Hurwitz panied by a vein the diameter of which was nearly (1996), there is a sphincter muscle around the 1 mm. opening of the common canaliculus into the lacrimal sac, and the sphincter prevents reflux. We did not find any valvular folds or a sphincter muscle at Discussion the common canaliculus-sac juction. However, we did find that the common canaliculus and lacrimal The results are schematically illustrated in sac were not connected directly but via transitional Figure 7. The non-keratinized and non-mucin- structures, the vestibule and infundibulum. The producing stratified squamous epithelium lined the lumen increases suddenly from the common canal- whole length of the lacrimal canaliculi and the iculus to the vestibule, and the common canalicular common canaliculus. The epithelium changed to end protrudes into the lumen of the vestibule. high pseudostratified columnar and then to low Tucker et al. (1996) attributed difficulty in cannu- pseudostratified columnar in the vestibule. The lating to the sac to kinking of the canaliculus-sac vestibule was an ample space that connected junction. Our results suggest that the difficulty in the narrow lumen of the common canaliculus to the cannulation may be primarily due to the small di- infundibulum of the lacrimal sac. There were two ameter of the lumen of the common canaliculus and structures that characterized the subepithelial con- the gap in luminal ampleness between the common nective tissue from the common canaliculus to the canaliculus and the vestibule. lacrimal sac: lymphoid structures and cavernous Maurice (1973) introduced 1% Evans blue into structures. his eye and examined the color of a nasal swab. Aubaret (1905) drew illustrations of the valves in Evans blue was consistently detected for six hours the lacrimal fluid drainage system. He called a fold after introduction of a 20 mm3, whereas no color extending from the superior wall of the junction was detected for six hours after introduction of between the common canaliculus and lacrimal sac 1 mm3. He therefore concluded that lacrimal flow is Rosenmuller's valve, and a fold from the inferior of the order of 0.6 mm3 per minute, and that lac- wall Huschke's valve. Scheaffer (1912) three- rimal fluid is absorbed in the lacrimal drainage dimensionally reconstructed the lacrimal canal- pathway. Doane (1981) and Hurtiwitz (1996) found iculus and sac but did not confirm the presence of evidence suppoting the possibility of lacrimal fluid such valves. Tucker et aL (1996) injected a plastic absorption in the passage from the lacrimal canal- compound through the lacrimal punctum and pre- iculus through the nasolacrimal duct. As shown in pared plastic casts of the lacrimal fluid drainage the present study, the vestibule and the more distal system. They also failed to find Rosenmuller's and portion of the lacrimal drainage system is lined with Huschke's valves in the canaliculus-sac junction, pseudostratified columnar epithelium. SEM exami- but instead found an acute kinking of the common nation of the lacrimal sac epithelium revealed the canaliculus at its junction with the lacrimal sac and presence of numerous cytoplasmic extrusions of conjectured that enlargement of the lacrimal sac different shapes and sizes, and we confirmed this

Plate II

Fig. 4. Paraffin section through the common canaliculus, vestibule, and infundibulum of the lacrimal sac. Note the narrow lumen of the common canaliculus (CC) compared with that of the inferior canaliculus (IC) and vestibule (Vb). The vestibule (Vb) is continuous with the infundibulum (I) of the lacrimal sac. The epithelium at the opening of the common canaliculus is stratified squamous (SE) but changes to high pseudostratified columnar (open arrow), and then into low pseudostratified columnar (closed arrow) in the vestibule. These changes are indicated by the bidirectional arrows in inset 4B. The subepithelial connective tissue contains free cell aggregations (= lymphoid structure, asterisks) and numerous venules (V) and capillaries (= cavernous structure). The arrowheads point cells containing brown pigments. S; Lacrimal sac, SC; Superior canaliculus. Fig. 5. Semithin section of the common canaliculus. Note that the epithelium is low pseudostratified columnar. There were numerous free cells consisting of lymphocytes, mast cells, plasma cells, and cells of unknown origin, in the connective tissue of the lamina propria (asterisk). There are numerous venules (V) and capillaries forming a cavernous structure. Fig. 6. Scanning electron microscopy view of the lacrimal sac epithelium. Columnar cells (PE) approximately 30 jim in height stand on the basal lamina (BM), and thus the epithelium is pseudostratified columnar. There are spherical cytoplasmic extensions on the apical surface but no micirovilli. Lacrimal Canaliculus and sac 159 160 R. Kominamiet al. PlateIII observation in histological sections. This means that References the lacrimal sac epithelium may excrete mucin and membrane-bound particles into the lumen. The os- 1) Adler FH. The lacrimal apparatus. In: Physiology of Eye, molarity values of freshly secreted lacrimal fluid 1950; pp 28-36, Henry Kimpton, London. 2) Aubaret E. Les replis valvularires des canalicules et du have varied with the investigator and are thought conduit lacrymo-nasal, au point de vue antomique et phys- to be equivalent to 0.9-1.4% NaC1 (Adler, 1950). iologique. Arch Opthalmol 1908; 28:211-236. However, investigators unanimously agree that lac- 3) Fernandez-Valencia R and Pellico LG. Functional anatomy rimal fluid loses water by evaporation and that the of the human saccus lacrimalis. Acta Anat 1990; 139:54-59. lacrimal fluid that reaches to the lacrimal sac is far 4) Hurwitz JJ. Physiology of the lacrimal drainage system. In: more concentrated than freshly secreted lacrimal The Lacrimal System, 1996; pp 23-28. Lippincott-Raven, Philadelphia and New York. fluid, and thus, that its osmolarity is greater than 5) Jones LT. An anatomical approach to problems of the 0.9% NaCl. This means that connective tissue fluid eyelids and lacrimal apparatus. Archs Opthalmol 1961; in the wall of the lacrimal sac may pass into the lu- 66:111-115. minal surface by simple diffusion. There were nu- 6) Maurice DM. The dynamics and drainage of tears. Int merous venules and capillaries from the common Opthalmol Clin 1973; 13:103-116. 7) Paulsen F, Thale A, Kohla G, Schauer R, Rochels R, Par- canaliculus to the lacrimal sac and they may supply waresch R and Tillmann B. Functional anatomy of human water to dilute the lacrimal fluid in the lumen. The lacrimal duct epithelium. Anat Embryo' 1998; 198:1-12. current of water from the subepithelial connective 8) Perra MT, Serra A, Sirigu P and Turno F. A histochemical tissue toward the lumen may facilitate the migra- and immunohitochemical study of certain defense mecha- tion of free cells in the lamina propria of the lac- nisms in the human lacrimal sac epithelium. Arch Histol Cytol 1995; 58:517-522. rimal sac into the sac lumen. 9) Schaeffer JP. The genesis and development of the nasolacrimal passages in man. Am J Anat 1912; 13:1-24. 10) Tucker NA, Tucker SM and Linberg JV. The anatomy of the common canaliculus. Arch Opthalmol 1996; 114:1231- 1234.

Plate III