Clinical Anterior Segment and Ocular Surface Findings Across Renal Replacement Modalities: Associations with CKD-Related Factors, Mineral Metabolism and Activin A

Background: Chronic kidney disease (CKD) is characterized by persistent inflammation, metabolic dysregulation, and mineral and bone disorder (CKD-MBD), all of which may affect ocular tissues. While retinal manifestations of CKD have been increasingly investigated, data regarding clinical anterior segment modifications and their relationship with systemic biochemical parameters remain limited. Methods: We performed a cross-sectional study including 130 participants: 53 non-CKD subjects, 29 patients undergoing maintenance hemodialysis (HD), and 48 kidney transplant recipients (KTRs). All participants underwent comprehensive ophthalmic examination, including best-corrected visual acuity (BCVA), intraocular pressure (IOP) measurement using Goldmann applanation tonometry, Schirmer I test, tear break-up time (TBUT) and assessment of cataract and blepharitis prevalence. Serum creatinine estimated glomerular filtration rate (eGFR), calcium, phosphate, parathyroid hormone (PTH), magnesium, 25-hydroxyvitamin D, and Activin A were recorded. Associations between ocular and systemic parameters were evaluated using correlation and regression analyses. Results: TBUT, Schirmer I and IOP did not differ significantly among groups (all p > 0.05). After adjustment for age, sex, BMI and diabetes mellitus (DM), HD patients showed worse visual acuity than the non-CKD reference group, reflected by higher logMAR BCVA values (adjusted B = +0.128, p = 0.024). In KTRs, higher corrected calcium was independently associated with reduced tear film parameters, correlating with both shorter TBUT (B = −0.903, p = 0.037) and lower Schirmer I values (B = −5.947, p = 0.008). Circulating Activin A increased progressively from controls to KTR to HD patients (median 189.5 vs. 273.0 vs. 314.0 pg/mL, p < 0.001) but showed no independent association with any anterior segment parameter; it was instead associated with cumulative glucocorticoid exposure (B = +1.602, p = 0.024). Conclusions: In CKD, clinical anterior segment and ocular surface differences were largely explained by age, sex, and comorbidity rather than renal replacement modality, with visual acuity deficit persisting in HD after adjusting for these covariates. At the individual level, corrected calcium was the parameter most consistently associated with tear film parameters in KTRs, whereas elevated Activin A was not independently associated with ocular involvement and likely reflects systemic disease activity.