Approach Considerations
Keratitis sicca is generally diagnosed on slit lamp examination. Laboratory testing, such as tear protein analysis and lactoferrin analysis, is also another good metric to help with the diagnosis.
Tear protein analysis allows the measurement of the lysozyme content of tears. Lysozyme accounts for approximately 20-40% of total tear protein content. The main disadvantages of this test include its lack of specificity in cases of meibomitis, herpes simplex keratitis, and bacterial conjunctivitis.
Lactoferrin has antibacterial and antioxidant functions. Lactoferrin analysis is commercially available through colorimetric solid phase and enzyme-linked immunosorbent assay (ELISA) technique. This study offers good correlation with other tests.
Osmolarity analysis, the measure of the salt content of the tear, is another commercially available measurement. This test is performed in a matter of seconds and can help give diagnostic information.
Histology and Impression Cytology
Pathologic examination of the lacrimal gland in patients with keratitis sicca reveals age-related changes, including lobular and diffuse fibrosis and atrophy, as well as periductal fibrosis. An underlying autoimmune mechanism (represented by round cell infiltration) may be present. No circulating autoantibodies are present in patients who do not have Sjögren syndrome with keratitis sicca.
Impression cytology
In advanced cases of keratitis sicca, the epithelium undergoes pathologic changes, resulting in squamous metaplasia and loss of goblet cells.
When the mucin layer of the tear is decreased (such as that associated with xerophthalmia or ocular cicatricial pemphigoid), squamous metaplasia and the following cytologic characteristics occur:
- Loss of goblet cells
- Enlargement and increase of cytoplasmic/nuclear ratio of superficial epithelial cells
- Keratinization
Impression cytology is highly sensitive; its main difficulty is the need for proper staining and expert microscopic evaluation of samples.
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