Excerpt from Keratoconjunctivitis, Sicca

Synonyms, Key Words, and Related Terms: dry eye syndrome, sicca syndrome, keratitis sicca, KCS, xerophthalmia

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Background: This condition is characterized by inadequate tear film protection of the cornea because of either inadequate tear production or abnormal tear film constitution, which results in excessively fast evaporation or premature destruction of the tear film.

Pathophysiology: The tear film is constituted by 3 layers, as follows: (1) a lipid layer (0.11 mm thick), produced by the Meibomian glands; (2) an aqueous layer (7.0 mm thick), produced by the main and accessory lacrimal glands of Krause and Wolfring; and (3) a hydrophilic mucin layer (0.02-0.05 mm thick), produced by the conjunctival goblet cells. Any abnormality of 1 of the 3 layers produces an unstable tear film and symptoms of keratitis sicca.

The tear layer affected most frequently is the aqueous layer, resulting in aqueous tear deficiency (ATD) or lacrimal hyposecretion. The classification scheme proposed by the 2 workshops held in December 1993 and December 1994 at the National Eye Institute (NEI) stratified patients with dry eye into those with aqueous tear deficiency and those with increased evaporative loss.

Sjögren syndrome is characterized by the combination of aqueous tear deficiency and dry mouth (xerostomia). Women comprise 90-95% of patients with this syndrome that has been classified into 3 different subsets, as follows:

Patients with systemic immune dysfunction but no defined connective tissue disease (primary Sjögren syndrome)

Patients who lack evidence of systemic immune dysfunction or a defined connective tissue disease

Patients who have a defined connective tissue disease, most commonly rheumatoid arthritis (secondary Sjögren syndrome). Dry eye is common in patients with rheumatoid arthritis, including those without Sjögren syndrome. Dry eye should always be taken into consideration regardless of the rheumatoid arthritis activity, because the severity of dry eye is independent of the rheumatoid arthritis activity.

All cases are characterized by progressive lymphocytic (predominantly B and CD4 lymphocytes) infiltration of the lacrimal and salivary glands that leads to disorganization of the normal gland architecture and consequent loss of function. At this time, the most comprehensive criteria for a diagnosis of Sjögren syndrome include the following:

Abnormally low Schirmer test

Objective evidence of low salivary flow

Biopsy-proven lymphocytic infiltration of the labial salivary glands

Dysfunction of the immune system as manifested by the presence of serum autoantibodies (eg, antinuclear antibodies, rheumatoid factor, anti-Ro [SS-A] and anti-La [SS-B] antibodies)

It has recently been shown that patients with keratoconjunctivitis sicca show elevated levels of tear nerve growth factor (NGF); these levels were decreased with 0.1% prednisolone. Data suggest that ocular surface NGF may play an important role in ocular surface inflammation processes associated with dry eyes.

Frequency:

In the US: Keratitis sicca is a relatively common condition, especially in older patients.

Mortality/Morbidity: Keratitis sicca can range from mild or barely symptomatic to moderate and severe cases, which can produce some of the following complications:

Punctate keratopathy, epithelial defects, sterile corneal ulcer, and infectious corneal ulcer

Corneal vascularization and corneal scarring

Corneal perforation

Race: No racial predilection exists.

Sex: Sjögren syndrome and keratitis sicca associated with this condition are significantly greater in women (9:1). Milder forms of keratitis sicca also are more common in females than in males.

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