Dry Eye Test Normal Values

A normal Schirmer I result without anesthesia is generally 10 mm or more of wetting in 5 minutes, with younger adults typically producing 15 mm or more. The TFOS DEWS II report uses 10 mm as the diagnostic cutoff below which dry eye should be suspected. Values below 5 mm indicate severe aqueous deficiency and are strongly associated with Sjögren's syndrome and other lacrimal gland disorders.

It depends on what you are trying to measure. Without anesthesia captures total tearing, which is the standard DEWS protocol and the most common choice for routine dry eye screening. With anesthesia better isolates basal secretion and is more useful when you suspect lacrimal gland failure or Sjögren's syndrome. Whichever method you choose, use the same protocol consistently across visits so serial comparisons are valid.

Schirmer I is the standard 5-minute strip test, performed with or without topical anesthetic, and is sufficient for most dry eye evaluations. Schirmer II adds nasal stimulation with a cotton-tipped applicator to maximally trigger reflex tearing after anesthetic instillation. It is rarely needed in routine practice, but it can help clarify whether a low Schirmer I result reflects true gland hypofunction or a reflex pathway deficit.

Variability is inherent because results are influenced by reflex tearing from strip contact, room lighting and humidity, strip placement consistency, patient hydration, anxiety, and systemic medications. Diurnal fluctuation in tear production adds another layer. Use the Schirmer test as a coarse severity marker rather than tracking small millimeter changes. If you need more repeatable serial data, consider phenol red thread testing or place more weight on symptoms, staining, and TBUT trends.

Modern practice generally favors eyes gently closed during the 5-minute test period. Closed-eye testing reduces variability from environmental factors such as humidity, temperature, air currents, and light-driven reflex tearing. The original Schirmer protocol used open eyes, but closed-eye testing has become more common because it produces more consistent results across visits.

A normal fluorescein TBUT is 10 seconds or longer, with healthy adults typically ranging from 10 to 35 seconds. Values of 5 to 10 seconds are borderline, and less than 5 seconds indicates clinically significant tear film instability. For non-invasive TBUT measured by instruments like the Keratograph, normal values are generally longer, with most cutoffs set at 10 to 12 seconds.

The most common driver is meibomian gland dysfunction. When lipid quantity or quality is reduced, the aqueous layer evaporates faster between blinks. Mucin deficiency from goblet cell loss, conjunctival scarring, or inflammatory conditions can also cause focal early break-up by preventing the tear film from spreading and adhering evenly across the ocular surface.

Yes. Fluorescein can alter tear film surface tension and often produces a slightly shorter measured TBUT compared with non-invasive methods. The volume and concentration of dye instilled also affect results. To minimize artifact, use a lightly moistened fluorescein strip rather than a full drop, avoid repeated instillation, and time from a natural blink after the dye has distributed evenly across the cornea.

If the time between blinks is longer than the TBUT, the tear film fails before the next blink and vision fluctuates. This relationship is captured by the ocular protection index (OPI): TBUT divided by interblink interval. An OPI below 1.0 means the surface is exposed to desiccation between blinks. This mismatch is common during screen use, when blink rate drops and incomplete blinks become more frequent.

Perform TBUT before Schirmer testing. The Schirmer strip induces reflex tearing and disrupts the tear film for several minutes, which can artificially improve a subsequent TBUT measurement. As a general rule, perform the least invasive tear film assessments first and work toward more disruptive tests, finishing with procedures such as lid eversion or meibomian gland expression.

A normal result is generally greater than 20 mm of color change in 15 seconds. Values of 10 to 20 mm are borderline and should be correlated with symptoms and other dry eye findings. Less than 10 mm supports aqueous deficiency, especially when reproducible and symmetric.

For routine screening and serial monitoring, many clinicians prefer it. The phenol red thread test is faster, more comfortable, and less reflex-driven, which improves repeatability and makes it easier to integrate into a busy workflow. Schirmer testing remains useful when you need continuity with historical Schirmer data or when evaluating patients against Sjögren's diagnostic criteria that specifically reference Schirmer cutoffs.

No. The test is designed to be performed without anesthesia. The thread is fine, placed on the palpebral conjunctiva rather than the cornea, and is typically well tolerated. Avoiding anesthesia preserves the natural tear film state and keeps the result closer to true resting tear volume.

Phenol red is a pH indicator embedded in the cotton thread. At the slightly acidic pH of the dry thread it appears yellow. When alkaline tears wick into the thread, the indicator shifts to orange-red. The measured length of the color change serves as a surrogate for the volume of tears that contacted the thread during the 15-second test period.

No, because they measure different things. The phenol red thread test estimates tear volume (aqueous quantity), while TBUT measures tear film stability (how quickly the tear film breaks between blinks). A patient can have normal volume but rapid break-up due to meibomian gland dysfunction, or low volume with surprisingly stable film. Using both tests together helps classify whether dry eye is primarily aqueous-deficient, evaporative, or mixed.