Conditions That Affect Schirmer Test Results
The Schirmer test is highly susceptible to variability from multiple technical, environmental, and patient-related factors that can significantly alter results and lead to misdiagnosis of dry eye disease. 1
Technical and Methodological Factors
Use of Anesthesia
- Schirmer I (without anesthesia) measures both basal and reflex tear secretion
- Schirmer II (with anesthesia) produces more variable results than testing without anesthesia 1
- The presence or absence of topical anesthesia fundamentally changes what you're measuring and the diagnostic thresholds
- Critical pitfall: When anesthesia is used, excess fluid must be gently removed from the cul-de-sac before strip insertion, or results will be falsely elevated 1
Strip Placement and Patient Behavior
- Eyelid position during testing dramatically affects results - closed eyelids produce significantly higher values (up to 13 mm/min difference) due to sustained reflex tearing 2
- Strip dislodgement occurs more frequently with open eyelids, invalidating the test 2
- Inconsistent methodology between visits will produce unreliable serial measurements
Environmental Conditions
Humidity Effects
Environmental humidity has a profound impact on Schirmer test results, particularly in patients without severe dry eye. 3
- Low humidity environments cause decreased wetting length through increased evaporation from the test strip itself
- Patients with moderate tear production may be falsely diagnosed with dry eye if tested in low-humidity conditions 3
- Severe dry eye patients are less affected by humidity changes because their minimal tear production limits evaporation effects 3
- The rate of strip wetting, not just final length, is affected by relative humidity changes 3
Temperature
- Higher room temperatures (30°C vs 23°C) significantly increase Schirmer values 4
- Testing should occur at a stable, comfortable room temperature for reproducibility
Patient Activity and Stimulation
Physical Activity
- Recent physical activity (such as stair climbing) dramatically increases Schirmer values for up to 20 minutes afterward 4
- Values can increase from baseline of 23 mm to 73 mm immediately post-activity 4
- Results normalize 20-30 minutes after activity cessation 4
Mechanical Stimulation
- Glandular massage increases tear production for approximately 10 minutes 4
- Nasal mucosa stimulation (Schirmer II test) triggers reflex secretion 1
Patient-Related Factors
Age
- While some studies suggest age effects, the relationship between age and Schirmer values remains inconsistent across research 5, 6
- Demodex colonization, which increases with age, is associated with lower Schirmer scores independent of age itself 5
Ocular Surface Conditions
- Demodex colonization significantly decreases Schirmer test scores in dry eye patients 5
- Neurotrophic keratopathy affects corneal sensation and can alter reflex tearing 1
Anatomical Factors
- Skull type/brachycephaly affects tear film stability but not necessarily Schirmer values 6
- Nasolacrimal duct patency does not significantly affect Schirmer results 6
Hormonal Status
- Hormone replacement therapy may affect Schirmer I (without anesthesia) but not Schirmer II (with anesthesia) 7
Critical Clinical Implications
To obtain reliable Schirmer test results:
- Test patients at rest (minimum 30 minutes after physical activity) 4
- Use consistent room temperature and humidity conditions 3, 4
- Maintain consistent eyelid position (preferably closed) across serial measurements 2
- Document whether anesthesia was used, as this fundamentally changes interpretation 1
- Never rely on a single abnormal result - serially consistent low results are required for diagnosis 1
The test has poor specificity (51%) compared to other dry eye metrics, reinforcing that it should never be used as the sole diagnostic criterion 1. The inherent variability from these multiple factors explains why the guidelines emphasize that Schirmer testing "gives variable results and should not be used as the sole criterion for diagnosing dry eye" 1.