Purpose <p>To evaluate the effects of 0.5% tropicamide on corneal topography and biomechanics in participants with keratoconus (KC), using the Pentacam static Scheimpflug imaging system and Corvis ST dynamic Scheimpflug imaging technology.</p> Methods <p>This study included 83 right eyes from 83 participants with KC. Mydriasis was induced by instilling 0.5% tropicamide eye drops three times at 10-min intervals. Thirty minutes after the final instillation, examinations were repeated using the Pentacam and Corvis ST. Measurement parameters included corneal topographic data (curvature-based parameters, elevation-based data, pachymetric values, integrated keratoconus indices and the Belin/Ambrósio total deviation value [BAD-D]) and biomechanical data (dynamic corneal response parameters, Vinciguerra screening parameters, Corvis biomechanical index and tomographic-biomechanical index). Violin plots were used to visualise the distribution patterns of the measured parameters. Differences between pre- and post-mydriatic measurements were analysed using paired <i>t</i>-tests.</p> Results <p>Following mydriasis, the Pentacam analysis revealed statistically significant decreases in front mean keratometry, front maximum keratometry, back mean keratometry, index of surface variance, central keratoconus index and BAD-D (<i>p</i> &lt; 0.05). In contrast, central corneal thickness, apex corneal thickness, thinnest corneal thickness and minimum sagittal curvature showed significant increases. Corvis ST biomechanical analysis demonstrated significant reductions in the time from the start to the second applanation, deformation amplitude of the corneal apex at the highest concavity and Corvis biomechanical index (<i>p</i> &lt; 0.05).</p> Conclusions <p>Mydriasis produced significant alterations in corneal topographic and biomechanical parameters in participants with KC. Although these changes do not affect the diagnosis of the condition, clinicians should be aware of them and adjust their treatment planning accordingly.</p>