LACRIMAL EXCRETORY SYSTEM

The excretory system is composed of the puncta, canaliculi, lacrimal sac, and nasolacrimal duct (see Chapter 1). With each blink, the eyelids close like a zipper-beginning laterally, distributing tears evenly across the cornea, and delivering them to the excretory system on the medial aspect of the lids. Under normal circumstances, tears are produced at about their rate of evaporation, and for that reason few pass through the excretory system. When tears flood the conjunctival sac, they enter the puncta partially by capillary attraction. With lid closure, the specialized portion of pretarsal orbicularis surrounding the ampulla tightens to prevent their escape. Simultaneously, the lid is drawn toward the posterior lacrimal crest, and traction is placed on the fascia surrounding the lacrimal sac, causing the canaliculus to shorten and creating negative pressure within the sac. This dynamic pumping action draws tears into the sac which then pass by gravity and tissue elasticity through the nasolacrimal duct into the inferior meatus of the nose. Valve-like folds of the epithelial lining of the sac tend to resist the retrograde flow of tears and air. The most developed of these flaps is the "valve" of Hasner at the distal end of the nasolacrimal duct. This structure is important because when imperforate in infants it is the cause of congenital obstruction and chronic dacryocystitis.

DISORDERS OF THE EXCRETORY SYSTEM

1. DACRYOCYSTITIS(Figure 4-14)

Infection of the lacrimal sac is a common disease that usually occurs in infants or postmenopausal women. It is most often unilateral and always secondary to obstruction of the nasolacrimal duct. In many adult cases, the cause of obstruction remains unknown. Dacryocystitis is uncommon in the intermediate age groups unless it follows trauma or is caused by a dacryolith. Spontaneous improvement follows passage of a dacryolith, but recurrence is the rule.

In infants, chronic infection accompanies nasolacrimal duct obstruction, but acute dacryocystitis is uncommon. Acute dacryocystitis in children is often a result of Haemophilus influenzae infection. Prompt and aggressive treatment should be instituted because of the risk of orbital cellulitis.

Acute dacryocystitis in adults is usually caused by Staphylococcus aureus or occasionally -hemolytic streptococci. In chronic dacryocystitis, Streptococcus pneumoniae or, rarely, Candida albicans is the predominant organism-mixed infections do not occur. The infectious agent can be identified microscopically by staining a conjunctival smear taken after expression of the tear sac.

Clinical Findings

The chief symptoms of dacryocystitis are tearing and discharge. In the acute form, inflammation, pain. swelling, and tenderness are present in the tear sac area. Purulent material can be expressed from the sac. In the chronic form, tearing is usually the only sign. Mucoid material can usually be expressed from the sac. It is curious that dacryocystitis is seldom complicated by conjunctivitis even though the conjunctival sac is constantly being bathed with pus exuding through the lacrimal puncta. Corneal ulcer occasionally occurs following minor corneal trauma in the presence of pneumococcal dacryocystitis.

Treatment

Acute dacryocystitis usually responds to appropriate systemic antibiotics, and the chronic form can often be kept latent with antibiotic drops. However, relief of obstruction is the only cure.

In adults, the presence of a mucocele is evidence that the site of obstruction is in the nasolacrimal duct and that dacryocystorhinostomy is indicated. The patency of the canalicular system is ensured if mucus or pus is regurgitated through the puncta on compression of the sac. Examination of the nose is important to ensure adequate drainage space between the septum and the lateral nasal wall. Dacryocystorhinostomy consists of forming a permanent anastomosis between the lacrimal sac and the nose. Exposure is gained by an incision over the anterior lacrimal crest. A bony opening is made in the lateral wall of the nose, and the nasal mucosa is sutured to the mucosa of the lacrimal sac. An endoscopic approach through the nose using lasers to help form the opening between the lacrimal sac and the nasal cavity is under investigation. Transluminal balloon dilation of the distal nasolacrimal system may also be useful for patients not suitable for surgery.

Excessive tearing (epiphora) is occasionally due to canalicular stenosis (see below) or obstruction at the junction of the common canaliculus and lacrimal sac. In either case, compression of the sac does not cause regurgitation of fluid, mucus, or pus through the puncta, and no mucocele is present. Intubation and irrigation of the canalicular system with a lacrimal cannula and x-ray studies with contrast media (dacryocystography) will identify the site of obstruction. Common canalicular obstruction may be treated by intubation of the passages with silicone stent for 3-6 months. A thick obstructing scar, however, will necessitate dacryocystorhinostomy and canaliculoplasty with silicone intubation of the canalicular system.

In infantile dacryocystitis, the site of stenosis is usually at the valve of Hasner. Failure of canalization is a common occurrence (4-7% of newborns), but normally the duct opens spontaneously within the first month. Forceful compression of the lacrimal sac will sometimes rupture the membrane and establish patency. If stenosis persists more than 6 months or if dacryocystitis develops, probing of the duct is indicated. One probing is effective in 75% of cases. In the remainder, cure can almost always be achieved by repeated probing, by inward fracture of the inferior turbinate, or by a temporary silicone lacrimal splint. Probing should not be attempted in the presence of acute infection.

2. CANALICULAR DISORDERS

Congenital anomalies of the canalicular system include imperforate puncta, accessory puncta, canalicular fistulas, and, rarely, agenesis of the canalicular system. Most cases of canalicular stenosis are acquired, usually the result of viral infections-notably varicella, herpes simplex, and adenovirus infection. Obstruction-even obliteration-may occur with Stevens-Johnson syndrome, pemphigoid, and other conjunctival shrinkage diseases. Systemic chemotherapy with fluorouracil and topical idoxuridine may also cause obstruction. Canaliculitis is an uncommon chronic unilateral infection caused by Actinomyces israelii (Figure 4-15), Candida albicans, or Aspergillus species. It affects the lower canaliculus more often than the upper, occurs exclusively in adults, and causes a secondary purulent conjunctivitis that frequently escapes etiologic diagnosis. Untreated, it will result in canalicular stenosis. The patient complains of a mildly red and irritated eye with a slight discharge. The punctum usually pouts, and material can be expressed from the canaliculus. The organism can be seen microscopically on a direct smear taken from the canaliculus. Curettage of the necrotic material in the involved canaliculus, followed by irrigation, is usually effective in establishing patency. Canaliculotomy is sometimes necessary. Tincture of iodine may be applied to the lining of the canaliculus after canaliculotomy. Recurrence is common.

Total canalicular obstruction necessitates use of an artificial tear duct for relief of epiphora (conjunctivodacryocystorhinostomy). A Pyrex glass tube is placed between the conjunctival sac and the nasal cavity.

Closure of the punctum is sometimes performed in patients with keratitis sicca to allow tears to remain in the conjunctival sac. Temporary closure may be done with silicone or collagen plugs in the canaliculi or by sealing the punctum with a hot cautery. The temporary obstruction will provide an opportunity to evaluate the effect. Permanent closure may be accomplished by deep cautery within the ampulla with thermal, electrocautery, or laser energy or by dividing the canaliculus surgically.

10.1036/1535-8860.ch4

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