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Tear Break-Up Time (TBUT)

Eye Care estimated about CNY 80-180

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Description

A clinical test measuring the time interval between a complete blink and the appearance of the first dry spot on the cornea, used to assess tear film stability in dry eye evaluation.

Main Uses

Primary clinical use is objective assessment of tear film stability in diagnosing and monitoring dry eye disease (DED); used to differentiate aqueous-deficient vs. evaporative subtypes when combined with Schirmer test and meibomian gland evaluation; guides treatment selection (e.g., lipid-based vs. aqueous-based lubricants); monitors therapeutic response (e.g., to cyclosporine, lifitegrast, or intense pulsed light); screens for ocular surface disorders pre-refractive surgery (e.g., LASIK); and evaluates occupational or environmental dry eye risk.

Normal Range

Tear Break-Up Time (BUT) is typically measured in seconds after a blink; normal range is 10–35 seconds. Values ≥10 seconds indicate stable tear film; 5–9 seconds suggest borderline instability; <5 seconds indicate significant tear film instability and are considered abnormal.

Low Values - Possible Causes

Dry eye syndrome (aqueous-deficient or evaporative), meibomian gland dysfunction (MGD), blepharitis, Sjögren’s syndrome, prolonged screen use or reduced blink rate, contact lens wear, vitamin A deficiency, ocular surface inflammation (e.g., allergic conjunctivitis), aging, and systemic medications (e.g., antihistamines, antidepressants, beta-blockers).

High Values - Possible Causes

Rarely clinically significant; may occur with excessive tear volume (e.g., epiphora due to lacrimal duct obstruction), recent topical lubricant application (artificial tears), corneal hypoesthesia (reduced blink reflex), severe corneal anesthesia (e.g., neurotrophic keratitis), or technical artifact (e.g., delayed fluorescein instillation, low room humidity causing slower evaporation). Note: BUT >35 seconds is uncommon and not routinely pathognomonic; high values are seldom clinically actionable.

Tear Break-Up Time Dry eye diagnosis Ocular surface evaluation

estimated about CNY 80-180