Purpose. The technique of orthokeratology (ortho-k) produces corneal changes as a result of the exerted pressure by the rigid contact lenses. This study aims at gaining a better understanding of the corneal changes produced in ortho-k treatment after the first night of contact lens wear. Methods. Fifteen subjects (fifteen eyes) worn CRT Paragon lenses for one night. The following day corneal curvature and corneal thickness was measured in different moments at the same predefined coordinates (after lens removal, and 3, 6 and 9 hours afterwards) with the Pentacam topographer. Results. A sample of 10 women and 5 men with a mean age of 26.10±3.15 and 22.40±1.43 years, respectively, participated in the study. In corneal curvature, anterior and posterior, no statistical differences were found. In contrast, in pachymetry a trend was observed showing the greatest difference between the baseline measure and the first measure after ortho-k lenses use. Conclusions. Corneal thickness changed with one night of ortho-k treatment. Corneal curvature does not show statistical differences. A larger sample is needed to obtain sounder conclusions given the high inter-subject variability of the results.