OBJECTIVE To measure changes in choroidal thickness (CT), retinal thickness (RT), and axial length (AL) accompanying intraocular pressure (IOP) increase and to investigate the changes in axial eye dimensions induced by IOP increase. METHODS Thirty-four eyes of 34 patients undergoing a diagnostic provocative test for primary angle closure (PAC). Patients with other macular diseases were excluded. Patients underwent the darkroom prone provocative test (DR-PPT) for 1 h. We measured CT and RT at the fovea by optical coherence tomography with the enhanced depth imaging method and AL with noncontact, partial coherence laser interferometry before and after the DR-PPT. RESULTS There was a statistically significant increase in the mean (SD) IOP of 7.3 (9.2) mmHg and the mean (SD) AL of 0.06 (0.12) mm after the DR-PPT (P < 0.001 and P = 0.014, respectively). There was a statistically significant decrease in the mean (SD) subfoveal CT of 30.0 (36.8) μm (P < 0.001), while there was no significant change in the mean foveal RT. The change in subfoveal CT was negatively correlated with the changes in IOP (r = -0.71, P < 0.001) and AL (r = -0.54, P = 0.004). CONCLUSIONS In eyes suspected of having PAC, acutely increased IOP accompanies choroid thinning and corresponding elongation of the optical axis.