Head tilt can impact the orientation of posterior pole images. Knowing this, a team of Canadian researchers conducted a study of 56 healthy patients to determine the effect of head tilt on image orientation measured by the fovea-Bruch’s membrane opening (FoBMO) angle with optical coherence tomography (OCT) imaging.

The researchers measured head tilt by affixing a smartphone with a built-in gyroscope to each patient's head. They then performed OCT imaging in both eyes at 0°, 5° and 10° of head tilt in the direction of the imaged eye (ipsilateral head tilt) and in the opposite direction (contralateral head tilt). For each image, the device software was tasked with determining the BMO center and the foveal pit from which the FoBMO angle was derived.

The team found that 38 (68%) of the patients were right-eye dominant and 18 (32%) were left-eye dominant. Each 1° head tilt resulted in a mean change of 0.76° in the FoBMO angle, they note, with no significant difference in effect between the two eyes. They add that the magnitude of the effect increased from 5° to 10°, however, and was similar for both ipsilateral and contralateral head tilt. They also discovered that ocular dominance did not modulate the effect of head tilt.

The study concludes that head tilt significantly affects OCT image orientation as measured by the FoBMO angle, presumably because cyclotorsion is not fully compensatory. The magnitude and direction of this effect does not depend on the dominant eye, the researchers add.

Mohammad S, Jarrar FS, Torres LA, et al. Impact of head tilt on optical coherence tomography image orientation. J Glaucoma. October 8, 2018. [Epub ahead of print].