Proteomic Analysis of Tear Film in Dogs and Cats: Emerging Biomarkers of Cognitive Dysfunction and Neurodegenerative Disorders

Cognitive dysfunction and neurodegenerative disorders represent an increasing clinical challenge in aging dogs and cats, while objective and minimally invasive biomarkers for early detection and disease monitoring remain limited. Tear film is a biologically active fluid reflecting both local and systemic processes and offers a practical, non-invasive source of potential biomarkers in geriatric veterinary patients. Proteomic analyses of canine and feline tear film have revealed a complex protein composition, including molecules involved in inflammation, oxidative stress, immune regulation, and cellular homeostasis—processes implicated in neurodegeneration. However, growing evidence from human and veterinary research emphasizes the importance of CNS-specific and mechanistically informative biomarkers, such as markers of axonal injury, synaptic degeneration, and glial activation, which may provide a more precise framework for interpreting peripheral proteomic alterations. This review summarizes current knowledge on tear film proteomics in dogs and cats and discusses its potential relevance to cognitive dysfunction and neurodegenerative processes. Particular attention is given to the integration of tear-derived proteins with validated blood and cerebrospinal fluid biomarkers, as well as to methodological challenges and future research priorities. With appropriate standardization and clinical validation, tear film proteomics may contribute to the development of novel diagnostic and monitoring strategies for neurodegenerative disorders in companion animals.