From the Guidelines
The tear osmolarity test is a diagnostic tool that measures the concentration of dissolved particles in tears to identify dry eye disease, with a principle based on the concept that hyperosmolarity is a hallmark of the condition, typically indicated by values above 308 mOsm/L 1. The test works by collecting a small sample of tears from the lower eyelid using a specialized handheld device, which is then analyzed to determine its osmolarity.
- In healthy eyes, tear osmolarity is maintained within a narrow range, typically between 290-300 mOsm/L.
- Elevated tear osmolarity indicates hyperosmolarity, which triggers inflammation and damage to the ocular surface, creating a cycle of worsening dry eye symptoms. Key points to consider when interpreting tear osmolarity test results include:
- A cutoff of 312 mOsms/L has been noted to have 73% sensitivity and 92% specificity for diagnosing dry eye 1.
- The test provides an objective measurement that correlates with dry eye severity, helping clinicians diagnose the condition earlier and monitor treatment effectiveness more accurately than subjective symptom assessment alone.
- Recent studies confirm that normal subjects have exceptionally stable tear film osmolarity, whereas tear osmolarity values in dry eye subjects become unstable quickly and lose homeostasis with environmental changes 1.
From the Research
Principle of the Tear Osmolarity Test
The tear osmolarity test is used to measure the concentration of solutes in tears, which can help diagnose and manage dry eye disease.
- The principle of the test is based on the idea that hyperosmolarity (high concentration of solutes) of the tear film is a key indicator of dry eye disease 2.
- Tear osmolarity is measured in milliosmoles per liter (mOsm/L), with normal values typically ranging from 280 to 308 mOsm/L 3, 2.
- The test can be performed using various devices, such as the TearLab osmometer or the I-Pen osmometer, which measure the osmolarity of tears collected from the tear meniscus or the palpebral conjunctiva 4.
Diagnostic Thresholds
- A threshold of 308 mOsm/L is often used to distinguish between normal and dry eye patients, with values above this threshold indicating hyperosmolarity 2.
- However, the optimal threshold value may vary depending on the device used and the population being tested 4.
- Intereye differences in osmolarity can also be used to diagnose and classify dry eye disease, with larger differences indicating more severe disease 2.
Limitations and Controversies
- Some studies have questioned the usefulness of tear osmolarity as a diagnostic tool, citing poor correlation with clinical signs of dry eye and high variability between devices 3, 5.
- Technical issues with the devices, reflex tearing, and difficulties in establishing a dry eye diagnosis may also affect the accuracy of the test 5.
- Further research is needed to fully understand the role of tear osmolarity in diagnosing and managing dry eye disease, and to establish standardized thresholds and protocols for its use 6, 4.