Disorders of the Lacrimal Apparatus in Infancy and Childhood



Disorders of the Lacrimal Apparatus in Infancy and Childhood


Donald P. Sauberan



EMBRYOLOGY

The lacrimal gland arises from the ectoderm of the superior conjunctival fornix at the 22 to 24 mm length of the embryo. Condensation of the surrounding mesenchyme leads to the development of the glandular stroma starting about the ninth week of development. This mesenchymal tissue is felt to arise from neural crest cells.

The lacrimal collection system is formed when the lateral nasal prominence and the maxillary prominence fuse at the 10 mm stage of embryonic development. At about the 15 mm stage, a double layer of epithelium is trapped within the space. It extends laterally to form the canalicular system and inferiorly to form the nasolacrimal duct. This epithelial cord is originally horizontal, but as the midface enlarges, it assumes the mature vertical orientation. Cavitation of this system begins to occur at about the third gestational month and continues until about the seventh gestational month. The last part of the nasolacrimal collection system to canalize is the very distal portion where the nasolacrimal duct empties into the inferior meatus in the nasal cavity (valve of Hasner). The valve of Hasner is often still closed at birth, but will spontaneously open during the first few months of life in the majority of cases.


LACRIMAL ANATOMY

There are two main tear-producing structures. The main lacrimal gland secretes reflexive tears in response to peripheral sensory, retinal, or psychogenic stimulation, such as those that occur with crying or reaction to an ocular irritant. The accessory glands of Krause and Wolfring are responsible for non-reflex basal tear secretion, which keeps the corneal surface lubricated. Tears are composed of three layers: an outer oily layer (secreted by the meibomian glands), a central aqueous layer (secreted by the lacrimal glands), and an inner mucinous layer (secreted by the conjunctival goblet cells). Once thought to be three distinct layers, it is now believed that there is mixing of the layers within the tear film.

The main lacrimal gland is located in the superotemporal orbit within the lacrimal gland fossa. It is divided into a larger orbital lobe and a smaller palpebral lobe by the lateral horn of the levator aponeurosis. The ducts of the lacrimal gland empty into the superior cul-de-sac approximately 5 mm above the lateral border of the tarsal plate. The ducts from the orbital lobe pass into the palpebral lobe, so any damage to the palpebral lobe can drastically reduce the outflow of tears from the lacrimal gland onto the corneal surface. The innervation of the lacrimal gland is complex. The afferent system is served by the lacrimal nerve, which is a branch off of the ophthalmic division of the trigeminal nerve (V1). The efferent secretory pathway begins in the lacrimal (salivatory) nucleus within the pons. Parasympathetic presynaptic fibers join the facial nerve that passes through the geniculate ganglion without synapsing. It leaves the facial nerve via the greater superficial petrosal nerve and joins the deep petrosal nerve to form the vidian nerve. This nerve travels to synapse in the pterygopalatine ganglion. Post-synaptic fibers are distributed to the lacrimal gland through the zygomatic branch of the maxillary branch of the trigeminal nerve (V3). They reach the lacrimal gland via an anastomosis between the zygomaticotemporal nerve and the lacrimal nerve. Sympathetic nerve fibers innervate the lacrimal gland as well, but appear to have no impact on secretion.

The accessory lacrimal glands of Krause and Wolfring are located near the conjunctival fornix and at the edge of the tarsal plate, respectively. There are 20 to 40 glands of Krause within the superior conjunctival fornix, and 2 to 8 within the inferior conjunctival fornix. There are 3 to 20 glands of Wolfring located at the upper border of the superior tarsal plate, and 1 to 4 at the lower border of the inferior tarsal plate. There may also be an accessory lacrimal gland within the caruncle or plica semilunaris. As mentioned previously, the accessory lacrimal glands are responsible for basal tear production that is necessary for adequate lubrication of the globe.

Evaporation plays a small role in the removal of tears from the ocular surface, but most tears are drained through
a series of collection channels and into the nose. The beginning of the tear drainage system is the lacrimal punctum (plural: punctae). The punctae are openings into the eyelid that sit on an elevation known as the lacrimal papillae. Each punctum lies approximately 6 mm lateral to the medial canthus; however, when the eyelids are open, the upper punctum lies about 0.5 mm nasal to the lower punctum. Normally, the punctae face inward within the tear lake. Each punctual opening is about 0.2 to 0.3 mm in diameter and open into the canalicular system. The ampulla is a 2 mm vertical section extending distally from the punctum perpendicular to the eyelid margin. The horizontal canaliculus then extends from the base of the ampulla toward the medial canthus curving with the eyelid and located just inferior to the eyelid margin. The 8 to 10 mm segment has a diameter slightly less than 1 mm, although elastic tissue surrounding the canalicular system allows for dilation to several times its width. In 90% of patients, the upper and lower canaliculi will join to form a common canaliculus that enters the lateral wall of the lacrimal sac. There are numerous infoldings at the junction of the canaliculus and lacrimal sac which creates a valve-like structure termed the valve of Rosenmuller. This structure helps prevent reflux of material from the sac into the canalicular system.

The lacrimal sac is located within the lacrimal fossa, formed by the frontal process of the maxilla and the lacrimal bone. The fossa and sac lay anterior to the orbital septum and are thus preorbital (not orbital) structures. The sac lies between the anterior of posterior crura of the medial canthal tendon. It is divided into a 3 to 5 mm portion above the canalicular opening known as the fundus, and the remaining distal portion (approximately 10 mm in length) known as the body. Because the majority of the sac is located inferior to the medial canthal tendon, conditions that affect the lacrimal sac (such as dacryoceles or dacryocystitis) are typically found inferior to the medial canthal tendon. Any process that involves the region superior to the medial canthal tendon should be met with suspicion, and an alternate diagnosis to a nasolacrimal disorder should be entertained. The nasolacrimal duct extends from the distal end of the lacrimal sac through the lateral wall of the nose to empty into the inferior meatus of the nose. The duct is approximately 12 mm long, and courses in inferior, lateral, and slightly posterior directions. The valve of Hasner is a fold of tissue that is present at the very distal end of the duct. This valve often does not “open” in infants, and is a common cause of infantile nasolacrimal duct obstruction. The nasolacrimal collecting system is lined with pseudostratified ciliated columnar epithelium, similar to that found in the upper respiratory system. Mucous-producing goblet cells are also present.

Most of the tear lake is actively pumped away from the eye by the actions of the orbicularis muscle. Jones (1) proposed that during eye closure the superficial and deep heads of the pretarsal orbicularis muscle compress the ampullae and shorten the horizontal canaliculus. At the same time the deep heads of the preseptal orbicularis, which are attached to the lacrimal sac fascia, contract, which expands the sac and creates negative pressure. This draws the tears from the canalicular system into the sac. When the eye opens, the orbicularis muscles relax and the resilience of the lacrimal sac fascia collapses the tear sac, forcing tears through the duct and into the nose. As the eyelids open and the puncta move laterally, the tears of the tear lake once again fill the ampullae and canaliculi. An alternative theory (Rosengren-Doane) suggests that the contraction of the orbicularis creates a positive pressure in the tear sac, which forces the tears into the nose, and as the eye opens the negative pressure created from re-expansion of the sac draws tears into the canaliculi when the puncta separate.


LACRIMAL TESTS


Dye Disappearance Test

The dye disappearance test (DDT) can be performed on nearly all children in the clinic. A drop of fluorescein (or a fluorescein strip wet with topical anesthetic) is placed into each conjunctival fornix and the patient is rechecked after 5 minutes. In a normal patient, there should be minimal (if any) fluorescein remaining. Fluorescein visualized after 5 minutes demonstrates obstruction, but does not localize the condition. The DDT is a physiologic test, as it involves no external means of forcing the tears into the collection system. Jones testing, which involves inserting a cotton-tipped applicator under the inferior meatus to collect fluorescein dye, is extremely difficult, if not impossible to perform on pediatric patients. In addition, diagnostic irrigation of the tear system will be resisted by children and can only be performed in more cooperative older patients.


Dacryocystography

Dacryocystography (DCG) is a radiographic test for evaluating the quality (not quantity) of tear outflow. It is particularly useful in the detection of lacrimal fistulae, neoplasms, and lacrimal stones. A radiopaque dye is injected into the lower canaliculus and serial films are taken at 15 and 30 minutes post-injection. This test has a limited use in the pediatric population. First, this test must be undertaken under general anesthetic in the majority of children. Second, the patient is exposed to a fair amount of radiation during the procedure (estimated at 3,000 mrad). Lastly, the majority of conditions that this test is most useful for are rare in the pediatric population.


Dacryoscintigraphy

Dacryoscintigraphy (DSG) is another radiographic test that provides a qualitative view of the lacrimal outflow. Ten microliters containing 100 microcuries of technetium-99m pertechnetate is dropped into each eye. Images are then taken four times per minute for 20 minutes. This test can
often be performed while awake, and radiation exposure is much less than with DCG (around 4 to 14 mrad). One can also investigate an anatomic blockage from a functional delay by having the patient perform various maneuvers during the test (such as forceful blinking).


CONGENITAL ANOMALIES OF LACRIMAL SECRETORY APPARATUS

Absence of the lacrimal gland is a rare condition that may present as chronic irritation of the conjunctiva and cornea from dryness, and is treated as such. Computed tomography shows no discernible lacrimal gland (2). Alacrima may also occur in association with conditions of other developmental anomalies, such as anophthalmos or cryptophthalmos, or may be inherited as an autosomal dominant or recessive trait.

“Crocodile tears,” or paradoxic gustolacrimal reflex, is unilateral tearing with mastication. This can be seen as a congenital defect, usually associated with an ipsilateral Duane syndrome or lateral rectus palsy. It is more commonly seen as an acquired condition, after a paralysis of the facial nerve, from trauma, or surgery.

Prolapse of the palpebral lobe of the lacrimal gland may occur, and the palpebral lobe can often be identified under the conjunctiva in the lateral aspect of the superior fornix. This should be recognized as normal tissue and left undisturbed, because surgical excision would transect the ducts from the orbital portion and could produce a dry eye.

Aberrant lacrimal tissue may be located elsewhere on the surface of the eye, under the conjunctiva. It may appear similar to a dermoid, except that it is not usually in the lower outer quadrant typical of dermoids. Aberrant lacrimal tissue appears as a slightly raised, well-vascularized, multicystic mass, and histopathologically it is often described as a choristomatous malformation containing a lacrimal gland, among other elements. Usually there are no symptoms, but excision may be performed for diagnosis or cosmesis. Aberrant lacrimal gland tissue may also occur within the sclera or in the eye.

Lacrimal secretory ducts may be absent or become obstructed, leading to distention and cystic development (dacryops) of the lacrimal gland. Rarely, a portion of the tears from the lacrimal gland may exist in the eyelid above the tarsus from a fistula. The opening is typically surrounded by hair, and excision with closure in layers should correct the condition.

Punctal agenesis can range from a simple veil overlying the punctual opening to a complete absence of the punctum (and often the surrounding canalicular system). The presence of appropriate lacrimal papillae will often indicate whether there is an actual opening underneath. Often a punctal opening can be made by inserting a sharp object (such as a safety pin) through the tissue overlying the punctum. This can be followed by a punctal dilator to expand the opening. Punctae may also be anomalous in position or number.

The canalicular system can have any multitude of congenital anomalies. Canalicular atresia can be proximal (adjacent to the punctum), midcanalicular, or distal (adjacent to or involving the opening into the lacrimal sac). The more significant the obstruction, the more significant surgical correction must be entertained.

A lacrimal sac diverticulum is a rare condition that presents as a mass below the medial palpebral ligament and may be uninfected or infected. When the lacrimal system is drained, however, a palpable or visible mass remains. Treatment consists of surgical excision of the diverticulum, suturing the closed wall of the lacrimal sac where the diverticulum originated. It can often mimic a dacryocystocele.

Jun 20, 2016 | Posted by in OPHTHALMOLOGY | Comments Off on Disorders of the Lacrimal Apparatus in Infancy and Childhood
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