Could tears help detect cognitive decline in dogs and cats?: full analysis
Version 2
A new review in Animals is making the case for tears as an underused diagnostic window into brain aging in dogs and cats. In “Proteomic Analysis of Tear Film in Dogs and Cats: Emerging Biomarkers of Cognitive Dysfunction and Neurodegenerative Disorders,” Dagmara Winiarczyk and Mateusz Winiarczyk argue that tear film could help fill one of the biggest gaps in veterinary cognitive medicine: the lack of objective, minimally invasive biomarkers for early detection and disease monitoring. (mdpi.com)
That idea arrives as cognitive dysfunction is getting more formal attention across companion animal medicine. The first working-group guidelines for diagnosis and monitoring of canine cognitive dysfunction syndrome were published in JAVMA in early 2026, describing CCDS as a chronic, progressive, age-associated neurodegenerative syndrome and identifying biomarker development as a future priority. An AAHA summary of those guidelines noted that there still aren’t commercially available biomarker tests for CCDS, even though multiple groups are working on them. (pubmed.ncbi.nlm.nih.gov)
The Winiarczyks’ review builds on a small but growing body of veterinary tear proteomics research. Earlier work from the same group reported that tear film from diabetic dogs showed proteomic differences, supporting the idea that tears can reflect systemic disease, not just ocular surface changes. Other veterinary studies have mapped the normal dog tear proteome, examined feline tear protein expression, and explored tear-based markers in conditions including glaucoma, conjunctivitis, and keratoconjunctivitis sicca. Taken together, that literature suggests the sample type is feasible, but disease-specific neurologic applications remain early-stage. (mdpi.com)
The biologic rationale is not coming out of nowhere. In human medicine, tear-based biomarker research is already being explored for Alzheimer’s disease, including studies showing differential proteins and microRNAs in tear fluid from patients with mild cognitive impairment and Alzheimer’s disease. The new veterinary review appears to draw on that translational logic: if tears can capture neuroinflammatory, metabolic, or degenerative signals in people, they may also help identify comparable processes in aging dogs and cats, especially given the overlap between canine cognitive dysfunction and human dementia biology. (pubmed.ncbi.nlm.nih.gov)
There’s also a broader biomarker race underway in veterinary neurology. A 2025 study in aged dogs found that plasma neurofilament light chain correlated strongly with age and cognitive decline, with the authors suggesting that pairing NfL with other markers such as GFAP and amyloid-related measures could improve diagnostic accuracy. That matters because it sets a benchmark: any tear-based biomarker platform will likely need to complement, not just conceptually resemble, emerging blood and CSF markers. (pubmed.ncbi.nlm.nih.gov)
Why it matters: For practicing veterinarians, the appeal of tears is obvious. Sampling is quick, repeatable, and far less invasive than CSF collection, while potentially easier to integrate into senior visits than advanced imaging or specialty referral workflows. If validated, tear proteomics could eventually support earlier workups, help distinguish cognitive decline from lookalike conditions, and give clinicians a more objective way to track progression or treatment response. But the review is better read as a roadmap than a ready-to-use diagnostic advance: current evidence supports plausibility, not clinical deployment. (pubmed.ncbi.nlm.nih.gov)
That caution is important because the field is still sorting out basic implementation questions, including which tear proteins are most informative, how collection methods affect results, and whether signals remain robust across breeds, ages, comorbidities, and ocular disease. For cats, the challenge may be even greater because feline cognitive dysfunction remains less characterized than CCDS, even though aging cats show neuropathologic similarities to human Alzheimer’s disease and may be especially well suited to longitudinal biomarker work. (pubmed.ncbi.nlm.nih.gov)
What to watch: Expect the next meaningful developments to come from prospective validation studies that compare tear proteomic signatures with cognitive screening results, neurologic exams, imaging, and established blood or CSF biomarkers, along with efforts to standardize tear collection and assay methods before any test can move toward routine practice. (pubmed.ncbi.nlm.nih.gov)