Saliva Conductivity as A Novel Screening Test for Dry Eye Disease and Sjögren's Syndrome

Dry eye disease is prevalent among patients presenting with ocular surface diseases, with rates ranging from 5-50% in recent years. In the United States, approximately sixteen million people are affected by this condition. Dry eye patients often experience ocular surface damage, such as punctate epithelial keratitis, superior limbic keratoconjunctivitis, and filamentary keratitis, due to impaired tear lubrication of the cornea. The etiology of dry eye disease is multifactorial, making diagnosis challenging and requiring comprehensive medical history inquiry and various ocular surface staining techniques. In Taiwan, fluorescein strips are commonly used to assess corneal damage severity and tear break-up time to evaluate tear film abnormalities. Recent research utilizing in vivo confocal microscopy has revealed lower sub-basal nerve fiber numbers and higher dendritic cell densities in the cornea of dry eye patients with immune causes.

Dry eye disease was redefined as a multifactorial condition at the International Dry Eye Workshop II (DEWS II) in 2017, categorized into aqueous deficient dry eye (ADDE) and evaporative dry eye (EDE). In Taiwan, Sjögren's Syndrome (SS) is a primary cause of aqueous deficient dry eye, occurring in approximately 4.8% of dry eye disease patients. SS is a chronic autoimmune disease characterized by lymphocyte infiltration of exocrine glands like the salivary and lacrimal glands. If SS occurs without other autoimmune diseases, it is referred to as primary Sjögren's Syndrome (pSS). Globally, the prevalence of pSS is approximately 60.82 per 100,000 people, with an incidence rate of 6.92 per 100,000 people. Conventional diagnostic methods for salivary dysfunction, such as salivary scintigraphy and parotid sialography, are costly and time-consuming. Following SS diagnosis, comprehensive blood tests, including CBC, DC, ESR, CRP, BUN, Cre, Na, K, HCO3, and serum immunomarkers (ANA, anti-SSA/Ro, anti-SSB/La, RF), are typically advised. The study aims to investigate saliva conductivity as a diagnostic and disease activity monitoring tool for primary Sjögren's syndrome in dry eye syndrome patients and its association with ocular surface damage and tear secretion volume.