The lacrimal system

Chapter 21 The lacrimal system





Introduction


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).




Lacrimal gland






Dry eyes in children




Acquired causes


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.


Isotretinoin treatment for acne is a cause of dry eyes in adolescence. This is usually reversible at cessation of the drug.


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.





The lacrimal drainage system







Congenital dacryocystocele


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.



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


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).

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Jun 4, 2016 | Posted by in OPHTHALMOLOGY | Comments Off on The lacrimal system
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