Background/Aims To investigate the time-dependent change of corneal endothelial cell (CEC) morphology and density (CECD) in patients with glaucoma post instillation of rho-associated protein kinase inhibitor ripasudil (Rip) 0.4% eye drops.

Methods This observational study involved 163 eyes of 163 patients with glaucoma in whom CEC morphological change was evaluated by CECD calculated via non-contact specular microscopy (NCSM) before and at 1 or 3 months post-Rip instillation. The change of CECD was plotted along with elapsed time from last instillation of Rip. The patients were divided into the following three groups based on the elapsed time post-Rip instillation: Early Group (<2 hours), Middle Group (≥2 hours, yet <6 hours) and Late Group (≥6 hours). The rate of CECD change was then analysed and compared among the three groups. An additional eight eyes of four patients with glaucoma were enrolled for a time-dependent study, with NCSM images evaluated before and at 1, 2, 3, 4 and 6 hours post-Rip instillation.

Results Morphological changes in the CECs appeared within 1 hour and recovered to normal within 6 hours post instillation. In the Early, Middle and Late Group, the median rate of CECD change as calculated by the NCSM automated software was −5.68%, −4.95% and −0.07%, respectively. The CEC images showed the same morphological changes with observational study in all four cases.

Conclusion Due to transient morphological changes, the NCSM software produced misleading data for determining CECD within 1 hour post-Rip instillation, yet revealed that CEC morphology gradually recovered to normal within 6 hours.