Impact of artificial tear viscosity and timing on keratometric measurements in cataract patients with and without dry eye disease: a randomized cross-over study

Abstract Background: Accurate keratometric assessment is essential for precise intraocular lens (IOL) power calculation in cataract surgery. Artificial tears are commonly used to optimize the ocular surface, yet their short-term effects on keratometric and biometric measurements remain uncertain. This study evaluated the impact of artificial tears with different viscosities on keratometry and optical biometry parameters in cataract patients with and without dry eye disease (DED). Methods: This prospective, randomized cross-over study included ۴۰ cataract patients (۲۰ with DED and ۲۰ with normal ocular surfaces). Each participant received high- and low-viscosity artificial tears on separate visits. Keratometric parameters (K۱, K۲), axial length (AL), anterior chamber depth (ACD), and calculated IOL power were measured using optical biometry at baseline and at ۳۰ s, ۲ min, and ۵ min after drop instillation. Results: Participants with DED were significantly older than those with normal ocular surfaces (P < ۰.۰۵), while sex distribution and intraocular pressure were comparable between groups (both P > ۰.۰۵). Both formulations induced significant transient changes in keratometric measurements, most evident at ۳۰ s and ۲ min post-instillation, with stabilization by ۵ min (within-group P < ۰.۰۵). These fluctuations were more pronounced in eyes with DED, particularly with high-viscosity drops, which showed large within-subject effect sizes. No significant differences in K۱ or K۲ were observed between groups at post-instillation timepoints (all P > ۰.۰۵). AL and ACD remained stable across all groups and timepoints (all P > ۰.۰۵). A modest but statistically significant reduction in calculated IOL power was observed only in DED eyes receiving high-viscosity artificial tears (P < ۰.۰۵). Conclusions: Artificial tears induce transient alterations in keratometric measurements, particularly within the first ۲ min after instillation and in eyes with tear film instability. High-viscosity formulations exert more pronounced effects and may influence IOL power calculations. To ensure accurate optical biometry, keratometry should be deferred for at least ۵ min following artificial tear instillation, especially in patients with DED. Keywords: cross-over trials artificial tears viscosities biometric analysis topography corneal anterior chambers eye axial length intraocular lens implantation phakic intraocular lens