Abstract Introduction The study of the post-mortem interval is an important element in the investigation of criminal acts. It is also one of the most difficult variables to quantify and establish. Various cadaveric phenomena are used to assess it, some of which are ocular, such as intraocular pressure. There are currently no reliable indicators of its behaviour over time. Material and methods Prospective, longitudinal, descriptive, and analytical study. Ante-mortem and post-mortem intraocular pressure was measured in seriously ill patients with progression to death, performing descriptive analysis of variables and application of the student’s t test, χ2 and ANOVA. Results Ninety-five eyes were studied, obtaining a mean ante-mortem intraocular pressure of 13.4 mmHg, which progressively decreased during the four hours post-mortem, 10.4 mmHg per hour, 8.48 mmHg at 2 h, 6.17 mmHg at 3 h, and 3.81 mmHg at 4 h. In the repeated measures ANOVA test, a clinically significant value of P Conclusions In this study, an inverse relationship was observed between post-mortem intraocular pressure and post-mortem interval, with a linear decrease over time of 2 mmHg per hour. Therefore, the measurement of intraocular pressure is a fast and reproducible method, which can be used as an additional element to estimate the post- mortem interval.