OBJECTIVE To examine the anatomical changes of the anterior chamber angle in the eyes of white patients using anterior-segment optical coherence tomography. METHOD An observational study of 122 white patients was performed to examine the changes of the iris and the anterior angle chamber using anterior-segment optical coherence tomography. Images were compared between healthy eyes of different age groups and patients with eyes having newly diagnosed ocular hypertension or glaucoma in different lighting conditions, using the interscleral spur line as a reproducible baseline. RESULTS In light illumination, the iris plane was posterior to the interscleral spur line and the iris was usually flat in 91.7% of healthy eyes in young persons. In 85.0% of healthy eyes in older persons and 92.5% of eyes in the group with ocular hypertension and glaucoma, the iris plane was anterior to the interscleral spur line and the iris was usually curved forward. In the dark lighting conditions, the pupil was dilated and the iris plane was more anterior, with narrowing or loss of the angle recess. Iridotrabecular contact was present in 67.5% of healthy eyes in older persons and 77.6% of patients with ocular hypertension or glaucoma. CONCLUSION The risk of iridotrabecular contact depends on the height of the iris plane relative to the trabecular meshwork and the degree of physiological dilation of the pupil. Open or narrow angles may become closed in dark lighting conditions, which can lead to the diagnosis of angle-closure glaucoma being missed.