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.
The tear film is constituted by 3 layers, as follows: (1) a lipid layer (0.11 µm thick), produced by the Meibomian glands; (2) an aqueous layer (7.0 µm thick), produced by the main and accessory lacrimal glands of Krause and Wolfring; and (3) a hydrophilic mucin layer (0.02-0.05 µm 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.
Keratitis sicca is a relatively common condition, especially in older patients.
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
No racial predilection exists.
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.
Decreased tearing is associated with increased age.
The following are the most common complaints in patients who are experiencing keratitis sicca depending on the severity of this problem:
Foreign body sensation and ocular dryness and grittiness, typically worse toward the end of the day
Ocular irritation (exacerbated by smoky or dry environments, indoor heating systems, prolonged reading, or computer use)
Excessive tearing (secondary to reflex secretion)
Documenting the history of exacerbating or alleviating factors and a systemic past medical history is important, including history of connective tissue disease, thyroid disease, and rheumatoid arthritis.
A review of systems focused on rheumatological disease, history of neoplasias, and GI and ear, nose, and throat (ENT) symptoms should be documented.
History of dry mouth should be requested.
A list of systemic and topical medications is important.
The following are the most important findings that are present in the external and slit lamp examination of patients with keratitis sicca before placement of any drops in the eye:
Perform a slit lamp examination to document some of the following:
Decreased tear meniscus
Increased debris in the tear film
Superficial punctate keratopathy (with positive fluorescein, lissamine green and/or rose bengal staining)
Mucous plaques and discharge
Xerostomia (in association with Sjögren syndrome)
Corneal epithelial defects or ulceration in more severe cases
Determine tear breakup time after placing a drop of fluorescein in the cul-de-sac.
Use rose bengal staining to look for conjunctival and corneal staining, particularly at the nasal and temporal limbus and/or inferior paracentral cornea.
Perform the 5-minute Schirmer test with and without anesthesia using a Whatman #41 filter paper 5 mm in width and 35 mm in length. (Wetting <5 mm with anesthesia and <10 mm without anesthesia are considered abnormal.)
Measure reflex secretion with a Schirmer II test if the initial Schirmer test is abnormal. The Schirmer II test is performed by irritating the nasal mucosa with a cotton-tipped applicator prior to measuring tear production with a Whatman #41 filter paper. (Wetting <15 mm after 5 min is considered abnormal.)
The causes for keratitis sicca are multiple and can be multifactorial. They can be classified into 3 categories by the element of the tear layer that is mostly affected, as follows: (1) those affecting the aqueous tear layer, (2) those affecting the lipid tear layer, and (3) those affecting the mucin tear layer.
The following include the most common conditions associated with aqueous tear deficiency:
Systemic vitamin A deficiency (xerophthalmia)
Lacrimal gland ablation
Collagen vascular diseases, including rheumatoid arthritis, Wegener granulomatosis, and systemic lupus erythematosus
Autoimmune disorders associated with Sjögren syndrome, as follows:
Chronic hepatobiliary cirrhosis
Lymphocytic interstitial pneumonitis
Progressive systemic sclerosis
Conjunctival scarring secondary to the following:
Drugs, including the following:
Infiltration of the lacrimal glands by sarcoidosis or tumors
Postradiation fibrosis of the lacrimal glands
The most common disorders associated with abnormalities of the lipid tear layer are as follows:
The most common conditions resulting in abnormalities of the mucin tear layer are as follows:
Vitamin A deficiency