Diagnostic Testing for Dry Eye
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1) Corneal and Conjunctival Staining: This is often part of a routine eye exam. The ocular surface is most commonly stained with fluorescein dye. The fluorescein is applied on a moistened sterile strip of paper to the inner lining of the lower eyelid or applied in an eye drop mixed with a topical anesthetic. The ophthalmic strips might be mildly irritating and the drop may briefly burn. When abnormal or missing epithelial cells are stained with fluorescein and observed under a blue light, they appear bright green. Bright green areas of the cornea may indicate dry eye as well as other conditions. Other less commonly utilized stains are lissamine green and rose bengal.
2) Tear break-up time (TBUT): The TBUT test is easily and quickly performed after fluorescein is instilled as described above. After the fluorescein is instilled, the patient is asked to stare without blinking. The cornea is observed under a blue light and time is counted in seconds, from the time of the last blink until a pocket of cornea appears that is no longer covered with fluorescein stained tears. The longer the TBUT, the more stable the tear film. A TBUT > 8-10 seconds is usually considered normal. 5-10 seconds is borderline and < 5 seconds suggests an unstable tear film and "dry" eye.
3) Schirmer's Test: A small paper strip with rulers printed along their length are placed inside the lower eyelids (inside the inferior conjunctival fornices) after the eyes are numbed with a topical anesthetic drop. The strips are removed after 5 minutes and the amount of tears produced in that time is read off of the strips (and measured in millimeters). Interpretations can vary but usually < 10mm of tear production in 5 minutes is suggestive of some form of dry eye.
4) TearLab: This in office test measures tear osmolarity. The test is a relatively painless and quick (seconds) and can be performed by an ophthalmic technician. Increased osmolarity indicates dry eye. A score over 300 mOsm/L or an intereye difference greater than 8 mOsm/L indicates dry eye.
5) LipiView: An interferometer is a noninvasive instrument that measures the amount of oil in the tear film. The measurements are obtained through images of the tear film that are captured over a 5 minute period.
Am J Ophthalmol. 2011 May;151(5):792-798.e1. doi: 10.1016/j.ajo.2010.10.032. Epub 2011 Feb 18. "Tear Osmolarity in the diagnosis and management of dry eye disease." Lemp MA1, Bron AJ, Baudouin C, Benítez Del Castillo JM, Geffen D, Tauber J, Foulks GN, Pepose JS, Sullivan BD.
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