Critical role of mass spectrometry proteomics in tear biomarker discovery for multifactorial ocular diseases (Review).

The tear film is a layer of body fluid that maintains the homeostasis of the ocular surface. The superior accessibility of tears and the presence of a high concentration of functional proteins make tears a potential medium for the discovery of non‑invasive biomarkers in ocular diseases. Recent advances in mass spectrometry (MS) have enabled determination of an in‑depth proteome profile, improved sensitivity, faster acquisition speed, proven variety of acquisition methods, and identification of disease biomarkers previously lacking in the field of ophthalmology. The use of MS allows efficient discovery of tear proteins, generation of reproducible results, and, more importantly, determines changes of protein quantity and post‑translation modifications in microliter samples. The present review compared techniques for tear collection, sample preparation, and acquisition applied for the discovery of tear protein markers in normal subjects and multifactorial conditions, including dry eye syndrome, diabetic retinopathy, thyroid eye disease and primary open‑angle glaucoma, which require an early diagnosis for treatment. It also summarized the contribution of MS to early discovery by means of disease‑related protein markers in tear fluid and the potential for transformation of the tear MS‑based proteome to antibody‑based assay for future clinical application.