Lactoferrin as a biomarker of ocular diseases and contact lens discomfort.

Lactoferrin (Lf) is frequently described as a diagnostic marker for different ocular diseases, such as dry eye (DE), Sjögren syndrome, and diabetic retinopathy. We therefore performed a meta-analysis on the average Lf concentration in healthy subjects and those affected by ocular diseases. The results suggest that Lf level is a good candidate as DE syndrome diagnostic biomarker, even though there is still a need for further development of standardized protocols of tear collection, processing and storage. To investigate Lf as a biomarker for contact lens (CL) discomfort, we developed a diagnostic method based on terbium fluorescence to detect Lf directly into human tears. Lf concentration was found to be unchanged after a period of CL wear and after a period of CL suspension. Instead, the results reveal a significant change in Lf affinity for terbium upon CL wear. An alteration of the protein conformational state or of its substrate-binding site leads to protein inactivation and triggers an inflammatory response. Indeed, high levels of protein denaturation have been found to be correlated with adverse effects, such as papillary conjunctivitis and CL discomfort.