Reproducibility in measuring tear samples using a freezing point depression osmometer

Area of Science:

• Ophthalmology
• Biomedical Engineering

Background:

• Tear hyperosmolarity is a key indicator in all forms of dry eye disease.
• Accurate tear osmolality measurement is crucial for diagnosis and management.
• Freezing point depression osmometry is a precise method for assessing tear fluid osmolality.

Purpose of the Study:

• To evaluate the inter-session reproducibility of the Fiske 110 freezing point depression osmometer.
• To compare the reproducibility of two different tear sample volumes (4 μl and 2 μl).
• To determine the clinical applicability of this osmometer in tear film research.

Main Methods:

• Tear osmolality was measured using the Fiske 110 osmometer with 4 μl and 2 μl tear samples.
• Samples were diluted to 20 μl (1:4 and 1:9 dilutions, respectively).
• Inter-session reproducibility was assessed in 40 healthy subjects over two sessions, one week apart.

Main Results:

• Both 4 μl and 2 μl sample volumes demonstrated acceptable inter-session reproducibility.
• The 4 μl sample volume exhibited a narrower bias range (-37.64/+35.94 mOsm/L) compared to the 2 μl volume (-48.43/+66.97 mOsm/L).
• No significant differences were found between sessions for either volume (p = 0.772 for 4 μl, p = 0.054 for 2 μl).

Conclusions:

• Both tested tear sample volumes provide acceptable reproducibility for osmolality measurements.
• The 4 μl tear sample volume, when diluted, is recommended for routine clinical tear film analysis due to its superior bias range.
• The Fiske 110 osmometer shows potential for clinical practice and tear film research.