ChapterAnatomy and 1 Physiology of the Nasolacrimal Ducts Chapter 1 1 Anatomy and Physiology of the Nasolacrimal Ducts 1 Friedrich Paulsen Core Messages! Q The lacrimal sac and nasolacrimal duct are surrounded by a cavernous body. While Q The tear film is produced by the lacrimal regulating the blood flow, the specialized gland and the different structures of the eye blood vessels permit opening and closing of lid. Its composition is controlled by the the lumen of the lacrimal passage affected by lacrimal functional unit. the bulging and subsiding of the cavernous body, while at the same time regulating tear Q The ocular surface epithelia together with outflow. The blood vessels are connected to the lacrimal gland produce a unique subset the vessels of the outer eye and could act as a of membrane bound and secretory mucins feedback signal for tear-fluid production. that stabilize the tear film, fix it to the epithelia, support binding of bacteria, and are of great importance to tear physiology. Q TFF peptides TFF1 and TFF3 of conjunctival Contents origin influence the rheological properties of 1.1 Introduction ................................... 1 the tear film. 1.2 Anatomy and Physiology Q Drainage of tears involves a number of of the Ocular Surface and Adnexa ................ 2 1.2.1 Ocular Surface ................................. 3 different mechanisms; of these the action of 1.2.2 Lacrimal Gland ................................ 4 the lacrimal part of the orbicularis oculi 1.2.3 Eyelid ......................................... 4 muscle is most important to bring tear fluid 1.2.4 The Lacrimal Functional Unit .................... 5 into the lacrimal sac. Epithelial secretion 1.3 Anatomy and Physiology products, the surrounding cavernous body, of the Nasolacrimal Ducts ....................... 6 and the arrangement of connective tissue 1.3.1 Innate Immune Mechanisms .................... 8 fibers are most important to drain lacrimal 1.3.2 Adaptive Immune Mechanisms .................. 9 fluid from the lacrimal sac into the inferior 1.3.3 Mechanisms of Tear Drainage .................... 10 meatus of the nose. 1.3.4 Absorption of Tear-Fluid Components ............ 12 1.4 Conclusion .................................... 13 Q The epithelium of the nasolacrimal ducts References ..................................... 13 eases tear flow by the production of mucins and TFF peptides. Moreover, it contributes to antimicrobial defense and is able to absorb 1.1 Introduction tear fluid components. Study of the nasolacrimal ducts is a synthesis of two disciplines, ophthalmology and otorhinolaryngology, which work closely together in the treatment of naso- lacrimal disorders. During recent years a bulk of new diagnostic and therapeutic methods, such as nasolac- 2 F. Paulsen rimal endoscopy, laser-assisted dacryocystorhinosto- nasolacrimal system; the latter consists of the upper 1 my, transcanalicular surgery, and interventional ra- and lower puncta, the paired lacrimal canaliculi, the diological therapies, have been applied to the lacrimal sac, and the nasolacrimal duct (Fig. 1.1). The nasolacrimal system; however, common knowledge nasolacrimal ducts collect the tear fluid from the about anatomy and physiology of the nasolacrimal ocular surface and convey it into the nasal cavity, ducts, and of tear flow through the nasolacrimal pas- whereas all other structures contribute to formation sage, is not well developed. of the preocular and cornea tear film. The tear film This chapter summarizes recent advances in serves to protect and lubricate the ocular surface, knowledge of the nasolacrimal ducts and discusses allowing for protection of the cornea and consistent them in conjunction with nasolacrimal duct physiol- clarity of vision. ogy. The preocular tear film contains water, protective antimicrobials, cytokines, lipids, and mucins, and is divided into three components: a lipid, an aqueous, 1.2 Anatomy and Physiology and a mucus component. The lipid component is se- of the Ocular Surface and Adnexa creted by the Meibomian glands in the eyelid and forms the superficial layer of the tear film (Fig. 1.2). To understand the physiology of tear flow through The aqueous component contains electrolytes, water, the nasolacrimal passage, and also its pathophysiolo- and a large variety of proteins, peptides, and glyco- gy (Chap. 2), basic knowledge of the whole lacrimal peptides, and is secreted primarily by the lacrimal system is necessary. The ocular surface and its adnexa gland as well as the accessory lacrimal glands (glands comprise the cornea, the conjunctiva with bulbar, for- of Krause, glands of Wolfring) of the lids (Fig. 1.2). nical and palpebral parts, the main lacrimal gland, The mucus component is the product of conjunctival and the glands of the eye lids, i.e., Meibomian, Moll, goblet and epithelial cells, corneal epithelial cells [4], Zeis, and accessory lacrimal glands as well as the and acinar as well as excretory duct cells of the lacri- Fig. 1.1. Ocular surface and nasolacri- mal ducts. The ocular bulbus with cornea and bulbar conjunctiva, as well as tarsal conjunctiva, are visible. At the medial rim of the upper and lower lid open the lacrimal puncta leading into the lacrimal sac via the upper and lower canaliculi. The lacrimal sac is situated in the orbital lacrimal fossa and proceeds into the nasolacrimal duct. The nasolacrimal duct is surrounded by a bony canal created by the maxillary and lacrimal bones and opens into the inferior meatus of the nose. Both lacrimal sac and nasolacri- mal duct are surrounded by a vascular plexus comparable to a cavernous body that is connected to the cavernous system of the nose. (From [26]) Anatomy and Physiology of the Nasolacrimal Ducts Chapter 1 3 Fig. 1.2. Structures of the eyelid. a Overview. Sagittal section area of the tasal plate near the rim of the eye lid. A non-cornified through an eye lid. tm tarsalis muscle, t tarsus, ppo palpebral squamous epithelium covers the underlying tarsal plate. Parts of part of orbicularis muscle, Mg Meibomian gland. White arrow: the Meibomian gland are visible. d The magnification shows an excretory duct of Meibomian gland; Mo Moll’s gland. Black accessory lacrimal gland (Krause’s gland; Kg). A small excretory arrows: sections through eyelashes. b–e Representative magnifi- duct opens into an infolding of the fornical conjunctiva (ar- cations of the areas marked by a large black arrow in a. rows). Above the gland parts of the tarsalis muscle (tm) are visi- b Conjunctival epithelium in the area of the tarsal plate near the ble. e Magnification of a part of a Meibomian gland (Mg) reveals fornix. The epithelium consists of columnar epithelial cells with its sebaceous character. The gland is embedded in the tarsal integrated goblet cells (arrows). Tight connective tissue of the plate. (Figure 2a is from [27], Figures 2b–e are from [6]) tarsus underlies the epithelium. c Conjunctival epithelium in the mal gland, which have recently been shown to pro- terface between the tear fluid and the epithelium that duce mucins (Fig. 1.2) [10, 16]. The mucinous layer stabilizes the fluid layer. That interface includes the helps to spread the lipid and aqueous layer across the undulating membrane ridges on the apical cell’s api- cornea. cal membrane, termed microplicae, and emanating from their apices, a layer termed the glycocalyx. Membrane bound mucins (MUCs 1, 4, and 16) of cor- 1.2.1 Ocular Surface neal and conjunctival epithelial cells are present in the glycocalyx layer. Soluble mucins (MUC5AC) from The surfaces of the ocular epithelia, both corneal and conjunctival goblet cells, as well as MUC5B and conjunctival, provide a specialized and important in- MUC7 from lacrimal glands, are in solution in the 4 F. Paulsen Table 1.1. Distribution of mucins and TFF peptides in the healthy lacrimal system 1 Localization Mucins TFF peptides Lacrimal gland MUC1 (membrane bound on acinar cells) MUC4, MUC5B, MUC7 (in acinar cells) MUC5AC (in excretory duct cells) Cornea MUC1, MUC4, MUC16 (membrane bound on epithelial cells) Conjunctiva MUC1, MUC4, MUC16 (membrane bound on epithelial cells) TFF1, TFF3 (in goblet cells) MUC5AC (in goblet cells) Nasolacrimal ducts MUC1, MUC4 (membrane bound on columnar cells) TFF1 (goblet cell associated); MUC2, MUC5AC, MUC5B (in goblet cells) TFF3 (in columnar cells) MUC5AC, MUC5B (in intraepithelial glands) MUC7 (in columnar cells) tear film (Table 1.1) [4, 10]. Both MUC5B and MUC7 tinction from serous salivary glands) into the inter- have been shown to bind bacteria and contribute to lobular ducts. The connective tissue between the acini innate immunity of the tear film. Besides MUC5AC, contains accumulations of lymphocytes as well as conjunctival goblet cells secret the trefoil family fac- many plasma cells mainly secreting IgA and being tor peptides (TFF peptides) TFF1 and TFF3 (Table 1.1) part of the eye-associated lymphoid tissue (EALT). As [6]. The TFF peptides are, together with mucins, typi- already mentioned, the lacrimal gland produces elec- cal constituents of mucus gels that influence the rheo- trolytes, water, as well as a large variety of proteins, logical properties of the tear film, promote migration peptides, and glycopeptides; of these, recent research of corneal epithelial cells, have antiapoptotic proper- regarding tear film rheology and innate immunity fo- ties, and induce cell scattering [5]. Conjunctival and cus on production of different constitutively and in- corneal epithelial cells are able to react against patho- ducible antimicrobial peptides [8], such as beta defen- gens by the production of inducible antimicrobial sins, surfactant proteins A and D [1], as well as mucins peptides (a kind of body-own antibiotics). In addition, MUC4, MUC5AC, MUC5B, and MUC7 which are se- in certain disease states the corneal cells are able to creted by the lacrimal gland into the tear film (Ta- produce TFF3. ble 1.1) [10, 16]. 1.2.2 Lacrimal Gland 1.2.3 Eyelid The lacrimal gland is anterior in the superolateral re- The “skeleton” of the eyelid is a collagen plate called gion of the orbit, and is divided into two parts by the the tarsus (Fig.