The Clinical Significance of Changes in the Precorneal Tear Film in Keratoconus in the Interpretation of Tomographic Methods of Corneal Examination

Relevance . Modern methods of corneal keratotopography and tomography play a key role in the diagnosis, monitoring, and surgical treatment planning of keratoconus (KC). However, the accuracy of measurements in KC may be affected by instability of the precorneal tear film (PTF) induced by dry eye syndrome (DES). Purpose : to evaluate the clinical significance of PTF changes in KC on the interpretation of corneal tomographic data and to develop an optimized diagnostic protocol for minimizing their impact. Patients and methods. The study included 115 patients (230 eyes) with bilateral non-operated KC. A comprehensive assessment of PTF status was performed (biomicroscopy of the anterior segment using vital dyes, tear film break-up time — Norn’s test, total and basal tear secretion — Schirmer’s and Jones’ tests), followed by Scheimpflug tomography (evaluating key topographic indices, kerato- and pachymetry, as well as elevation, asphericity, and wavefront aberrations) before and after instillation of sodium hyaluronate-based artificial tears. Results . The results revealed significant PTF instability in KC patients, manifested by reduced tear film break-up time and high corneal staining intensity. After temporary PTF stabilization with artificial tears, a significant decrease was observed in anterior corneal surface indices (ISV, IVA, KI, CKI, IS, IHD), keratometry values (K1, K2, Kmean, Kmax), and aberrations (RMS total, LOA, HOA). Strong correlations were found between PTF status and topographic parameters: positive with staining ( r = 0.621–0.787) and negative with tear film break-up time ( r = –0.334 to -0.787). Conclusion . PTF impairment in KC significantly distorts tomography results, potentially leading to misdiagnosis of disease progression. Instillation of artificial tears prior to examination improves measurement accuracy by minimizing PTF instability-related artifacts. Implementing standardized PTF assessment and correction in the diagnostic algorithm for KC patients enhances data reproducibility and clinical decision-making reliability.