Anatomy, Physiology, and Immunology of the Lacrimal System



Fig. 3.1
Anatomy of the lacrimal punctum and its surrounding tissues. This section is performed parallel to the tarsal plate (Masson’s trichrome stain)





Anatomy of the Lacrimal Canaliculus


The lacrimal canaliculus is divided into the vertical and horizontal portions [1, 2, 6]. Its transitional part occasionally dilates to form an irregular dilated cavity or ampulla (Fig. 3.2) [6]. The length of the vertical portion is 2 mm and that of the horizontal part is 10 mm [6]. The medial most 2 mm of the horizontal portion mostly forms the common duct or canaliculus [5, 9], and more than half of this part runs in the wall of the sac. The punctum and vertical canaliculus are encircled by a similar hard fibrous tissue. This fibrous tissue in the vertical canaliculus contains skeletal muscle fibers, called the muscle of Riolan (Fig. 3.1) [10]. The epithelium of the canaliculus is a nonkeratinized stratified squamous epithelium, similar to the punctum (Fig. 3.3) [10]. As the canalicular wall contains much elastic fibers (Fig. 3.4), its diameter can be changed to enlarge or shrink as needed. Although the diameter of the canaliculus is usually 0.3–0.6 mm [1, 8], it can be expanded to over 1.0 mm. The temporal 4/5 part is directed posteronasally and surrounded by the Horner’s muscle, occasionally called the lacrimal part of the orbicularis oculi muscle (Fig. 3.5) [8]. In the nasal 1/5 part, the Horner’s muscle directs posteriorly away from the canaliculus (Fig. 3.5) [8]. Although the canaliculus usually directs anteronasally after separation from the Horner’s muscle (Fig. 3.5), it occasionally directs posteronasally in cases with proptosis (Fig. 3.6) [8]. The superior canaliculus courses, in general, almost straight to the internal common ostium, but the inferior canaliculus changes the course superiorly before joining the superior canaliculus. The course of the inferior canaliculus to be independently emptying into the sac has not been known so far.

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Fig. 3.2
Gross anatomy of the ampulla of a lacrimal caruncle. A left lower eyelid sagittally incised. Yellow arrow – ampulla


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Fig. 3.3
Epithelia of the lacrimal caruncle and the sac. The canaliculus shows a nonkeratinized stratified squamous epithelium and goblet cells in part. This specimen demonstrates the stratified columnar epithelium extending to the canaliculus (Masson’s trichrome stain)


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Fig. 3.4
Elastic fibers of a canalicular wall. This specimen contains a lot of elastic fibers in the canalicular wall. A sinus of Maier is shown here, into which the canalicular part is expanded (Elastica van Gieson stain)


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Fig. 3.5
Relationship between the lacrimal canaliculus and the Horner’s muscle (Masson’s trichrome stain)


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Fig. 3.6
Connection of common lacrimal canaliculus to sac. A common canaliculus occasionally empties into a sac from superiorly. A common fascia is seen between the sac and the Horner’s muscle (Masson’s trichrome stain)


Anatomy of the Common Lacrimal Canaliculus


More than 95 % of the upper and lower canaliculi join to become the common canaliculus to reach the common internal ostium [5, 11]. The canaliculi empty into the sinus of Maier (Fig. 3.7) and those independently pouring into the sac are <2 % [11]. Sinus of Maier needs further elaboration. The common internal ostium is the part where the common canaliculus pours to the sac. However, the common canalicular cavity does not simply connect with the sac lumen. A laterally bulged portion of the sac, called the sinus of Maier, is occasionally formed around the common internal ostium and some canaliculi empty to this portion (Fig. 3.7) [11]. An expanded common canaliculus can also be called the sinus of Maier (Fig. 3.4) [11].

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Fig. 3.7
A sinus of Maier, in which a part of sac is expanded. The superior and inferior canaliculi separately empty into the sinus of Maier (Masson’s trichrome stain)

The common canaliculus has a nonkeratinized stratified squamous epithelium. However, the transitional area with the stratified columnar epithelium of the sac with some goblet cells is occasionally seen in the common canaliculus (Fig. 3.3) [8]. To the contrary, the stratified squamous epithelium of the common canaliculus sometimes extends to the sac lumen (Fig. 3.8) [8].

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Fig. 3.8
Connection of common lacrimal canaliculus to sac. A stratified squamous epithelium in a canaliculus occasionally extends into a sac (Masson’s trichrome stain)

A protuberance (fold) is shown, although only a half of cases [9], at the junction between the common canaliculus and the sac [12]. This structure is called the valve of Rosenmüller [5, 6]. The common internal ostium largely opens by temporal traction of the Horner’s muscle during eye closing, but there is a nasal movement of the ostium as well [13]. Therefore, the part around the common internal ostium needs a structure dealing with this nasal movement and this may be the real reason for a valvular presence in this region. The sinus of Maier could have also been evolved for the same reason.


Anatomy of the Lacrimal Sac and Its Fossa


The lacrimal sac and the nasolacrimal duct are a continuous structure [14]. The part within the lacrimal sac fossa is called as the “sac,” and the part inferior to the superior opening of the nasolacrimal canal is the “nasolacrimal duct.” [14] The part of the sac superior to the medial canthal tendon (MCT) is called the fundus, with its vertical length of 3–5 mm [14]. The body of the sac, inferior to the MCT, is about 10 mm in length. The epithelium of the sac is a stratified columnar epithelium (Figs. 3.3, 3.6, and 3.8) [15] and contains goblet cells, cilia, and serous glands [16]. The epithelial surface shows microvilli [17, 18]. Although the sac wall is constituted with a cavernous structure, it is fairly thin and less developed than that of the nasolacrimal duct [16, 19]. The lateral aspect of the sac wall is covered by a fascia, and its posterior portion is a common fascia with the Horner’s muscle (Fig. 3.6), which is called the “lacrimal diaphragm” [14].

The lacrimal sac fossa comprises of the anterior frontal process of the maxillary bone and the posterior lacrimal bone [9]. There are ridges anteriorly and posteriorly, which are called the anterior or posterior lacrimal crest, respectively (Fig. 3.9) [5]. The suture between the maxilla and the lacrimal bone is situated in various ways, and some take its site close to the posterior lacrimal crest. A process is formed between the inferior portion of the posterior lacrimal crest and the orbital face of the maxilla, which is called the hamular process (Fig. 3.10) [6]. A groove is shown nasal to the anterior lacrimal crest which is called the sutura notha [5], sutura longitudinalis imperfecta [6], or pseudo-suture [20]. It is not considered as a true suture but a vessel groove formed by a branch of the inferior orbital artery [9].

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Fig. 3.9
Anatomy of lacrimal sac fossa and its surrounding tissues


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Fig. 3.10
A right lacrimal sac fossa, seen from temporally

The superoinferior length of the lacrimal sac fossa is 12–15 mm, anteroposterior 4–9 mm, and the width 2–3 mm (Figs. 3.9 and 3.10) [9]. The lacrimal sac fossa shows shorter anteroposterior length superiorly [21, 22]. As the lacrimal sac fossa opens temporally, the sac lumen is usually large enough. The long axis of the fossa inclines about 10° poteriorly [23] (Fig. 3.11) and directs about 10° temporally [24] (Fig. 3.12). The angle range of the long axis of the fossa is 0–20° posteriorly [23] and 1–30° temporally [24].

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Fig. 3.11
A posterior inclination of lacrimal sac fossa and nasolacrimal canal. The nasolacrimal canal inclines more posteriorly than the lacrimal sac fossa. Line Pink: base line, Line Yellow: long axis of lacrimal sac fossa, Line Blue: long axis of nasolacrimal canal


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Fig. 3.12
A horizontal inclination of lacrimal sac fossa and nasolacrimal canal. Lacrimal sac fossa goes temporally without exception. Nasolacrimal canal is mostly parallel to the vertical base line. Line Pink: base line, Line Yellow: long axis of lacrimal sac fossa, Line Blue: long axis of nasolacrimal canal


Clinical Correlations




1.

The orbit is defined as the part posterior to the orbital septum [9]. The lacrimal apparatus is not an orbital tissue as it is located anterior to the orbital septum. However, according to vicinity with the eyelid as an extra-septal tissue, the lacrimal system is closely related to the eyelid and relies on the eyelid movement for pump functions of the lacrimal drainage. Since the function of the lacrimal apparatus is highly specialized, it is defined as the “lacrimal system” with an independent identity of its own.

 

2.

When an acute dacryocystitis extends around the sac, the inflammation goes toward the eyelid because of the above reason. In an advancing stage, it occasionally goes into the orbital space, since the barriers are not strong enough.

 

3.

The lacrimal bone is too thin with its thickness around 0.1 mm [5]. Therefore, in both external and endonasal dacryocystorhinostomy, an osteotomy is made from the lacrimal bone. In cases of a lacrimo-maxillary suture being situated close to the posterior lacrimal crest, a surgeon occasionally feels difficulty to perform the osteotomy. In an external dacryocystorhinostomy, initial osteotomy sometimes begins at the part around the sutura notha [21]. It is better, however, not to extend the osteotomy toward the ethmoid sinus to prevent bleeding from the ethmoid mucosa.

 

4.

In an endonasal dacryocystorhinostomy, relationship between the lacrimal sac fossa and the base of the middle turbinate is vital (Fig. 3.13). The base of the middle turbinate, called the “axilla,” often corresponds to the lacrimal sac fossa (Fig. 3.14) [15], although there are exceptions. A high sac position is defined as the sac situating superior to the axilla, and a low sac is a position inferior to the axilla [15]. This relative position between the lacrimal sac fossa and the axilla is confirmed with a preoperative CT or intraoperative light pipe inserted from a punctum (Fig. 3.14). A light cannot be occasionally seen in cases with thick frontal process of the maxilla, posterior location of the lacrimo-maxillary suture, cases with high sac position, or cases with anterior protrusion of the ethmoid air cells with wide distance between the lacrimal bone and the lateral wall of the nasal cavity.

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Fig. 3.13
Overview of a lateral nasal wall


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Fig. 3.14
Relationship between lacrimal sac fossa and axilla. A light is seen through the bone

 

5.

Endoscopic clinical anatomy reveals that the posterior portion of the lacrimal bone is covered in considerable cases by the uncinate process forming the most anterior part of the ethmoid air cells [25]. The inferoposterior part of the lacrimal bone tends to be covered largerly [25]. A small protuberance called the agger nasi is seen over the lacrimal sac fossa (Fig. 3.13) [25]. Aerated agger nasi (agger nasi cell) can often reach the lacrimal sac fossa [25].

 

6.

The uncinate process is, as its name, a bony process with a “hook” (Fig. 3.15) [15, 26]. This hook part is situated at a considerable depth corresponding to the posterior hiatus semilunaris. As the tail of the uncinate process faces anteriorly, we cannot easily see the “hook” part around the lacrimal sac fossa [26].

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Fig. 3.15
Tip of a right uncinate process. The hook part directs posteriorly

 


Anatomy of the Nasolacrimal Duct (NLD) and Canal


The lacrimal sac and the nasolacrimal duct are a continuous tissue, and anatomically speaking, the “nasolacrimal duct” (mucosal portion) is the part inferior to the superior opening of the nasolacrimal canal (bony portion) [14]. The nasolacrimal canal is formed by the lacrimal bone superonasally, the inferior turbinate bone inferonasally, and the maxillary bone temporally [5]. The superior opening is about 6 mm in diameter and, in general, is an ellipse with a little longer horizontally (Fig. 3.16). The supero-inferior length of the canal is fairly short, about 12 mm [14] (Fig. 3.12). Although the longitudinal axis of the canal directs about 20° posteriorly [23] (Fig. 3.11), it directs almost vertically in most cases [24]. The nasolacrimal canal empties into the superior part of the inferior meatus (Fig. 3.12).

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Fig. 3.16
Superior view of the opening of nasolacrimal canal (Yellow arrows)

The angle range of the long axis of the nasolacrimal canal is 3–40° posteriorly [23]. The frontal view shows the angle range from 12 ° nasally to 11° temporally and mostly directs vertically around 0° [24]. Although a general consensus of the canal course is “temporal,” occasionally cases with medial course have been noted.

The nasolacrimal canal does not have a constant diameter throughout its length: some shows narrower and others larger [27]. Two thirds to 3/4 of cases show the narrowest part at the superior opening, but the others have found the narrowest portion at 3.5–5.5 mm from the superior opening [27]. These narrowings may have a bearing on the etiopathogenesis of primary acquired nasolacrimal duct obstructions (PANDO) [27].

Epithelium of the NLD is a stratified columnar epithelium, similar to the lacrimal sac, and contains goblet cells and serous glands [15]. In general, the goblet cells are distributed more inferiorly, but several specimens have also demonstrated considerable number of goblet cells throughout (Figs. 3.17, 3.18, and 3.19). Although the cavernous structure is shown similar to the lacrimal sac, it is much more developed than the sac [16, 19] (Figs. 3.17 and 3.18). The wall is more thickened inferiorly and most show a funnel shape lumen (Fig. 3.20). Cilia are similar to the nasal mucosal cells [18]. The microvilli on the epithelial surface contribute to reabsorption of the lacrimal fluid [17, 18].

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Fig. 3.17
A vertical slice from lacrimal sac to nasolacrimal duct. The bd are enlarged photos in each part of the a. (b) Sac epithelium, (c) superior nasolacrimal duct epithelium, (d) inferior nasolacrimal duct epithelium. Numbers of goblet cells are increasing as we proceed inferiorly. The b does not show a goblet cell, but the Figs. 3.3, 3.5, 3.6, and 3.8, similarly showing lacrimal sac, demonstrate goblet cells. The bd are the same scale. The asterisk in the (c) indicates the goblet cell (Masson’s trichrome stain)

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May 26, 2017 | Posted by in OPHTHALMOLOGY | Comments Off on Anatomy, Physiology, and Immunology of the Lacrimal System
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