Name

Vers une approche holistique du film lacrymal

Tear film layer is a complex fluid subjected to multifactorial variations: circadian, physiological (age, sex, pregnancy), psychological, environmental and, sometimes, its alteration can be associated with ocular surface diseases. Therefore, we aimed at investigating the principal components of this fluid (proteins, lipids, carbohydrates, and aqueous layer) in order to follow the algorithm: composition – structure – function relationships.

Tear and serum samples from patients with ocular allergy (100 eyes, 62 patients) were evaluated versus an healthy control group (n=10). Fern-like crystalloids from tear fluid desiccation on a glass surface were examined using infrared spectroscopy (Spotlight 400 FTIR Imaging System) in order to characterize the molecular conformational/structure of tear lipids, glycolipids, proteins and glycoproteins. Tear microdesiccates were analyzed in the mid infrared spectral range (700-3000 cm-1) to obtain infrared maps. Tear protein fingerprints were evaluated using the Agilent 2100 Bioanalyzer in combination with the Protein 230 Plus LabChip Kit, investigating tear proteins in the range of 14-200 kDa. Total and specific IgE from sera and tears were analyzed with Unicap 100 – Phadia SAS. Among the overall tear electrophoregram, particular attention was paid to three protein peaks at 26 KDa, 59-61 KDa and 75 KDa, respectively corresponding to immunoglobulins light chain (26 KDa), albumin and IgG heavy chain (59-61 KDa) and secretory IgA (sIgA) heavy chain (75 KDa). IgG and albumin (Alb) are known to cross the blood-tear barrier as a result of increased vascular permeability and inflammation. We compared these bands to the ratio (R) IgE analyzed/IgE transudated, R>4 corresponding to an IgE local production and R<4 to an IgE transudate from serum.

The infrared analysis of fern-tests showed a morphological and spectral homology between lipids (and/or glycolipids), proteins (and/or glycoproteins) and some crystalloid forms obtained. Between four distinctive morphological zones (zone I, II, III and transition band), no morphostructural homology was found. Moreover, in R>4 tear samples, our results showed an important decrease of the inflammatory biomarkers linked to IgG and Alb peaks.

Fern-test, tear protein electrophoregram, tear specific and total IgE assessment, tear lipids, glycolipids and glycoproteins evaluation represent the different laboratory approaches that can be routinely performed, allowing a global tear film evaluation in terms of composition, structure, and functions. 

Given the variability of the tear film layer, its overall analysis is required to direct or to confirm the clinical diagnosis.