A Systematic Review on Dry Eye Syndrome in Patients with Diabetes Mellitus: Prevalence, Etiology, and Clinical Characteristics

Background: Dry eye syndrome (DES), or keratoconjunctivitis sicca, is a common ocular surface disorder characterized by tear film instability, inflammation, and ocular discomfort. Diabetes mellitus (DM) is increasingly recognized as a major risk factor for DES due to metabolic, neuropathic, and vascular complications. However, the prevalence and clinical spectrum of DES in diabetic populations remain heterogeneous across studies. Objective: This systematic review aims to evaluate the prevalence, etiological mechanisms, and clinical characteristics of dry eye syndrome among patients with diabetes mellitus. Methods: A systematic literature search was conducted in PubMed, Scopus, Web of Science, Cochrane Library, and Google Scholar for studies published between January 2000 and July 2025. Observational studies, clinical trials, and meta-analyses reporting on prevalence, pathophysiology, and clinical features of DES in diabetic populations were included. Data on prevalence, diagnostic tools (Schirmer test, tear break-up time [TBUT], ocular surface disease index [OSDI]), and odds ratios (OR) were extracted. The quality of studies was assessed using the Newcastle-Ottawa Scale. Results: A total of 45 studies comprising over 10,000 diabetic patients were included. The prevalence of DES varied from 17.5% in community-based studies (China) to 54.3% in hospital-based settings (India), with a pooled prevalence of approximately 38–40%. Diabetic patients had a significantly higher risk of DES compared to non-diabetics (OR: 1.82; 95% CI: 1.23–2.67). Etiological factors included lacrimal gland dysfunction, Meibomian gland disease, corneal nerve damage, and hyperglycemia-induced inflammation. Clinical signs such as reduced Schirmer values (<5 mm/5 min) and decreased TBUT (<10 s) were common, often exceeding patient-reported symptoms due to diabetic neuropathy. Conclusion: Dry eye syndrome is a frequent and underrecognized complication of diabetes mellitus, strongly associated with poor glycemic control and disease duration. Routine screening and early management of DES should be integrated into diabetic eye care. Future research should focus on standardized diagnostic protocols, longitudinal studies, and tailored interventions to improve ocular and systemic outcomes.