Chapter 21 The lacrimal system
The lacrimal system consists of a secretory portion and a drainage system. The secretory portion is the lacrimal and accessory lacrimal glands. With the meibomian glands and the goblet cells, they secrete the components of the tear film. The tear film has three layers: the inner mucin layer secreted by the conjunctival goblet cells, the intermediate aqueous layer secreted by the lacrimal and accessory lacrimal glands, and the outer, oily layer secreted by the meibomian glands. The accessory lacrimal glands produce basal tear secretion; the lacrimal gland is responsible for reflex tearing in response to noxious or emotional stimuli.
The drainage system consists of the lacrimal puncta, canaliculi, lacrimal sac, and the nasolacrimal duct. This active system pumps tears from the conjunctival sac into the inferior meatus of the nose.
Tears flow along the lid margins and conjunctival fornices. They are spread across the surface of the eye by blinking. Tears protect the eye by surface lubrication, provision of oxygen and antibacterial substances such as IgA, IgG, and lysozyme, and mechanical removal of irritating substances and cellular debris.
Lacrimal problems in children usually relate to underproduction of tears, causing dry eyes, which is rare but potentially sight-threatening, or reduced drainage of tears, which is much more common but less serious (Box 21.1).
Causes of watery eyes in children
The lacrimal gland develops from ectoderm that is supported by mesodermal connective tissue. It continues to grow 3–4 years after birth. Basal tearing is present in infants from birth, and reflex tearing begins at any time from birth to several months of age.1
The lacrimal gland is an exocrine gland in the anterior aspect of the supratemporal orbit within the bony lacrimal fossa. The majority of the gland lies within this fossa, but the lateral horn of the levator palpebrae superioris separates this orbital part from the palpebral lobe, which extends anteriorly into the supratemporal conjunctival cul-de-sac. The ducts of the gland pass through the palpebral lobe and open on to the conjunctiva in the superior fornix. The lacrimal gland is innervated via the facial (afferent) and trigeminal (efferent) nerves. The accessory glands of Kraus and Wolfring sit in the superior conjunctival fornix.
Congenital absence is rare, usually occurring in conditions with reduced conjunctiva: anophthalmos, cryptophthalmos, and the lacrimo-auriculo-dento-digital (LADD) syndrome. Anomalous lacrimal ductules that secrete tears on to the skin rather than the conjunctival sac may be found near the lacrimal gland, around the lateral canthus, or in the preauricular region. These are rare but may require dissection and excision.2
Other congenital anomalies include orbital ectopic lacrimal gland tissue. A drainage system may not be present in such cases and an enlarging orbital mass may develop. Neoplasms can occur with such ectopic tissue.
Congenital alacrima is rare. It may be due to absence of the lacrimal gland or to it being ectopic in the orbit. Alacrima may be associated with systemic conditions such as the Riley-Day syndrome (familial dysautonomia), anhydrotic ectodermal dysplasia, and Allgrove’s syndrome (familial alacrima, achalasia of the cardia, and adrenal deficiency) (see Chapter 98).
Acquired tear deficiency may be due to pathology of the lacrimal gland, causing failure of tear production, or to conjunctival damage (see Chapter 31), leading to ductule obliteration. The lacrimal gland may be damaged by Epstein-Barr infection, as the result of HIV infection, or in patients with bone marrow transplantation (often associated with graft-versus-host disease). The conjunctiva may be affected by injury (burns), infection, the sequelae of trachoma, Stevens-Johnson syndrome, or toxic epidermal necrolysis.
Sjögren’s syndrome is rare in children. It can be a primary autoimmune event or associated with rheumatoid arthritis or systemic lupus erythematosus. Children with Sjögren’s syndrome often have lacrimal gland enlargement. They may have recurrent parotid gland swelling and salivary gland involvement. Sjögren’s syndrome should be considered in any child with recurrent parotiditis, keratoconjunctivitis sicca, and early tooth decay due to xerostomia.4
Chronic blepharitis is uncommon. It usually presents with recurrent chalazia, although the lids may appear normal. The associated poor quality tear film causes patches of dryness and may lead to peripheral corneal vascularization and scarring which can be sight-threatening.
Children with dry eyes present with irritable, uncomfortable, gritty, red eyes. A reduced tear meniscus is evident with punctate keratopathy, particularly affecting the interpalpebral zone. Staining occurs with fluorescein and Rose Bengal dyes. Severe keratopathy due to concomitant corneal hypoesthesia can be a problem in the Riley-Day syndrome.
Treatment of dry eyes involves copious use of artificial tears and temporary or permanent punctal occlusion in severe cases. Immunomodulation may have a role to play in secondary lacrimal gland failure including that due to infections. Blepharitis should be treated with lid hygiene, lubricants, and systemic antibiotics such as erythromycin or azithromycin. Oral tetracyclines should be avoided in children prior to their second dentition.
Dacryoadenitis is usually associated with viral infection, mumps, infectious mononucleosis, herpes zoster, tuberculosis, brucella, histoplasmosis, or gonococcal infection. Lacrimal gland swelling may rarely be a sign of childhood Sjögren’s disease.
A primary clinical feature of dacryoadenitis is the “S sign” in which there is drooping of the lateral aspect of the upper lid. In acute inflammatory cases, the overlying skin is inflamed. Neuroimaging confirms enlargement and helps rule out other orbital masses. In the long term, dacryoadenitis may damage the lacrimal gland and cause reduced tear secretion.
Lacrimal tumors are very rare in children. Pseudotumor causing painful swelling may affect the lacrimal gland.5 Malignant epithelial tumors, including mixed cell adenocystic and other carcinomas, have been recorded in childhood.6
Lacrimal gland enlargement is also found in conditions such as sarcoidosis or leukemia. Prolapse of the lacrimal gland, which is commonly bilateral, may present as a subconjunctival mass in the upper outer fornix. This may occur with craniofacial anomalies (see Chapter 28) due to reduced orbital volume and increased orbital pressure.
The lacrimal outflow system develops between the maxilla and the lateral nasal process from surface ectoderm. By the end of the first trimester this tissue begins to canalize. The puncta usually open with the eyelids during the sixth month of gestation. The nasolacrimal duct opens into the inferior meatus of the nose just before or after term birth. There may be a failure of this canalization process at any part of the system, but this is most frequent at the lower end.7
The puncta should be in contact with the globe at the medial aspect of the upper and lower lids. The proximal part of the canaliculus, the ampulla, is a slightly dilated vertical portion 1 mm in length in the young child. The canaliculus then turns 90° to run medially in a horizontal direction. The upper and lower canaliculi join to form the common canaliculus that enters the lateral wall of the lacrimal sac. Rosenmüller’s valve prevents reflux of tears from the sac into the canaliculus. The lacrimal sac sits in the bony lacrimal fossa, separated from the middle meatus of the nose by the maxilla and lacrimal bone. The lacrimal sac extends superiorly under the medial canthal ligament to form its fundus. The nasolacrimal duct exits from the lower end of the sac and passes in a downward, lateral, and slightly posterior direction. This duct is surrounded by bone in its upper part but becomes membranous inferiorly. The nasolacrimal duct opens into the medial wall of the inferior meatus of the nose via the valve of Hasner. This ostium is found under the inferior turbinate of the nose, approximately 1 cm directly behind the entrance of the nose in the baby.
Tears are actively pumped through the outflow system. During blinking, when the lids close, the canaliculi are shortened and narrowed by contraction of the pretarsal orbicularis muscles. Simultaneously the same muscles pull the lateral sac wall, creating negative pressure inside the sac, sucking fluid into the expanded sac. Further lid closure causes contraction of the orbicularis oculi muscle, which squeezes the tears from the sac into the nasolacrimal duct. At the end of each blink, the sac is empty. As the lids open, the canaliculi and the sac elastically expand. This causes a vacuum within the system into which tears enter via the puncta, and the cycle begins again.
Common abnormalities, include narrowing (stenosis), blockage (atresia), complete absence (agenesis), or duplication (accessory channels) of any part of the system. A membranous obstruction at the distal end of the nasolacrimal duct is the commonest abnormality, causing congenital nasolacrimal duct obstruction.7 Obstruction at other sites is rare, but more relevant in older children.
Children with craniofacial abnormalities (see Chapter 28), particularly clefting syndromes, have complex anomalies of the lacrimal outflow system that may involve large areas being either blocked or absent.
A dacryocystocele is a congenital swelling located at the medial canthus due to trapped fluid inside the lacrimal sac and nasolacrimal duct.8 The fluid is unable to escape from either the upper or lower end of the drainage system as both are blocked. This presents as a tense, blue, non-pulsatile swelling below the medial canthus. It is evident at, or shortly after, birth (Fig. 21.1A). The inferior end of the dacryocystocele projects into the nose (Fig. 21.1B) and in some cases may be responsible for breathing difficulties.9 If respiratory compromise occurs, urgent treatment is required.
Fig. 21.1 Congenital dacryocystocele. (A) A bluish swelling is seen below the medial canthal tendon. It can present as nasal obstruction. (B) Dacryocystocele viewed from inside the nose, demonstrating the dilated nasolacrimal duct protruding into the nasal cavity, which may cause respiratory distress (left nostril).
Congenital dacryocystocele must be differentiated from a meningoencephalocele, a meningocele, a mid-line nasal dermoid cyst (see Chapter 29), or a capillary hemangioma (see Chapter 20). An MRI scan is helpful in identifying the dilated sac and nasolacrimal duct and excluding other pathology. Routine imaging is unnecessary; the diagnosis is usually made clinically.
Treatment of a dacryocystocele involves observation during the first 2 weeks of life, during which time most spontaneously improve. If it has not settled by this stage, if acute dacryocystitis (Fig. 21.2) or respiratory difficulties develop, then endoscopic drainage of the dacryocystocele into the nose is indicated and the nasal mucosa over the dacryocystocele excised. If acute dacryocystitis has intervened, intravenous antibiotics should be given prior to surgery.
Congenital nasolacrimal duct obstruction represents a delay in maturation of the lacrimal system where it enters the nose, resulting in a persistent membranous obstruction at the valve of Hasner. The diagnosis is made on a history of a watery eye that has been present from the first few weeks of birth. This is usually unilateral but may be bilateral. If so, it is commonly asymmetrical. Some children develop a mucopurulent discharge that may be constant or intermittent. The eye remains “white” without evidence of active infection, although conjunctivitis may complicate the condition. The child is well with no evidence of irritation or photophobia. The skin around the eye may become red and excoriated. Although usually an isolated abnormality, congenital nasolacrimal duct obstruction may be more frequent in certain conditions, such as EEC syndrome (ectrodactyly, ectodermal dysplasia, clefting; Fig. 21.3) branchio-oculo facial syndrome,, craniometaphyseal or craniodiaphysial dysplasia, Down’s syndrome,, LADD syndrome, and the CHARGE association (Table 21.1).