Osteology

Regarding anatomical considerations [19-21], the bony aspects of the nasolacrimal excretory system exist at the medial wall of the anterior orbit and extend to the lateral wall of the nasal wall. The lacrimal fossa of the orbit is composed of the maxilla anteriorly and the lacrimal bone posteriorly. The lacrimal fossa is a shallow depression bounded by the anterior lacrimal crest and the posterior lacrimal crest. The maxillo-lacrimal suture runs vertically within the lacrimal fossa. At the inferior aspect of the depression is the ostium of the nasolacrimal duct which extends through the maxillary bone and exits under the inferior turbinate of the nose (Fig. 9.1).

Anterior Lacrimal Crest

Fig. 9.1. The fossa for the lacrimal sac lies anterior to the lamina papyracea of the medial orbital wall. It is bordered by a rounded anterior lacrimal crest (thick arrow) and a sharply defined posterior lacrimal crest (thin arrow). Direct mid facial trauma can cause displacement of the lacrimal sac associated with fractures

Fig. 9.1. The fossa for the lacrimal sac lies anterior to the lamina papyracea of the medial orbital wall. It is bordered by a rounded anterior lacrimal crest (thick arrow) and a sharply defined posterior lacrimal crest (thin arrow). Direct mid facial trauma can cause displacement of the lacrimal sac associated with fractures

9.2.2 Soft Tissue

The described osteology serves as a scaffolding for both the suspensory elements of the eyelid and the lacrimal excretory system. The anterior lamellae of the eyelid consists largely of skin and the orbicularis muscle. The orbicularis, which acts as the protractor of the eyelids, has a complex arrangement to where it originates at the medial wall. At this origin, the prese-ptal orbicularis is divided into a superficial head and deep (Jones muscle) head. The superficial head extends from the anterior rim of the medial canthal tendon which itself originates from the anterior lacrimal crest. The deep head of the preseptal orbicularis originates at the lacrimal sac and its connective tissues.

The pretarsal orbicularis is adherent to the tarsus of the upper and lower eyelids. This is also split into superficial and deep (Horner's tensor tarsi muscle) segments. The deep head extends from 4 mm posterior to the posterior lacrimal crest. This muscle's posterior orientation allows for proper contour of the medial canthus and appropriate apposition of the eyelids to the medial aspect of the eye globe. The superficial horns of the pretarsal orbicularis inserts on the anterior edge of medial canthal tendon.

The complex arrangements of the muscles allows for a lacrimal pump of positive and negative pressures which helps move the tears within the palpebral fissures through the lacrimal excretory system. Bony and soft tissue traumatic injury to these structures may eliminate "lacrimal pump" physiology.

The lacrimal system begins at the lacrimal punctum which starts at the myocutaneous junction of the medial aspect of the lid margin of upper and lower eyelids. The punctum are surrounded by a fibrous ring called the lacrimal papilla which is in turn surrounded by the pretarsal orbicularis.

The canaliculi extends form the punctum to the lacrimal sac. The caniliculus initially has a vertical path of 2 mm followed by a medial extension toward the lacrimal sac. The medial extension (8-10 mm) follows a horizontal pathway hugging the contour of the eyelid margin. As the canaliculi approach the lacrimal sac, they tend to combine to form the common canaliculus. This final pathway enters the lateral wall of the lacrimal sac slightly above the vertical midpoint of the sac.

The lacrimal sac lies within the bony depression of the medial orbital wall, called the fossa of the lacrimal sac. The sack measures 12 mm in height, 4-6 mm in depth, and 2 mm in width. The shape is pisciform with a narrower top and wider lower portion. The fe i

Fig. 9.2. The lacrimal drainage system includes the punctum (double arrow), the canaliculi (vertical down arrow) , lacrimal sac (thick arrow), and naso-lacrimal duct (left arrow). Soft tissue lacerations may include distal and proximal canaliculi while bony trauma can affect the lacrimal sac and the naso-lacrimal duct sack is bound by the fossa medially, the medial can-thal tendon superiorly, and muscle and orbital septum inferomedially.

The lacrimal duct measures 3-4 mm in diameter and extends inferiorly 12.5 mm vertically. The upper part of the duct runs through the maxilla while the inferior part runs within the nasal mucosa of the lateral nasal wall. The mucosa lining of the duct exits at the lateral wall of the nasal passage of the inferior meatus. The flap of mucosa at this exit is referred to as the Valve of Hasner. Both the lacrimal sac and duct can be injured with facial and nasojugal lacerations in addition to being obstructed with orbit and maxillary fractures (Fig. 9.2)

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