Diagnostic Value of Conjunctival Impression Cytology and Nelson Grading in Evaluating Dry Eye Disease in Ankylosing Spondylitis

<i>Background and Objectives</i>: Ankylosing spondylitis (AS) is a chronic inflammatory disorder frequently associated with acute anterior uveitis; however, it may also predispose individuals to dry eye disease. We aimed to evaluate dry eye in AS participants employing both conventional tests and conjunctival impression cytology (Nelson grading) to compare their sensitivity in detecting ocular surface changes. <i>Materials and Methods</i>: This prospective case-control study enrolled 24 patients with AS and 27 age- and sex-matched healthy controls. Dry eye was evaluated using the Schirmer I test (measuring tear production), fluorescein tear break-up time (BUT, assessing tear film stability), the Ocular Surface Disease Index (OSDI) questionnaire (evaluating symptoms), and conjunctival impression cytology (analyzing ocular surface changes). Intergroup differences were assessed using non-parametric statistical methods, and their correlations with clinical variables were examined. <i>Results</i>: Nelson conjunctival cytology scores were significantly higher in AS patients than control subjects (1.63 ± 0.92 vs. 0.74 ± 0.86; <i>p</i> = 0.001), indicating greater conjunctival goblet cell loss and squamous metaplasia. In contrast, Schirmer, BUT, and OSDI observations did not differ significantly between AS and control subjects (all <i>p</i> > 0.05). Within AS, the Nelson cytology grade did not correlate accompanied by tear test observations or disease activity indices, and symptom scores did not align accompanied by Schirmer or BUT values. <i>Conclusions</i>: AS patients demonstrated evidence of subclinical dry eye changes detectable by impression cytology even when standard tests were normal. Conjunctival cytology was more sensitive than Schirmer, BUT, or symptom assessment in identifying ocular surface involvement in AS. Integrating such ocular surface evaluation into AS management could allow earlier diagnosis of dry eye and prompt intervention to improve patient quality of life.