The relationship between clinical measurementand measurement from computed tomography for ocular and head dimensions

This study compares measurements taken by routine clinical means with those taken from computed tomography (CT) images. Ocular and head dimensions were measured. Correlation between techniques was reasonable for all parameters except exophthalmos. The correlation coefficient improved for measurement of exophthalmos when thin (5 mm) axial sections were used, however there were occasional large discrepancies in measured values. In general, measurement from CT scans gave smaller values than direct measurement, though interpupillary values were larger when measured from CT images. The results show the importance of choosing a mid-orbital axial scan plane and avoiding tilt of the scan plane for accurate measurement from CT images. Consistency in measurement techniques is also important for comparative measurements over time.