The reliability of Hertel exophthalmometry. Observer variation between physician and lay readers.

In order to quantify and characterize the interobserver variation in exophthalmometry and to assess the impact of experience on that variation, four observers of varying levels of experience obtained an exophthalmometer reading from 100 subjects' right eyes and 97 subjects' left eyes. Observers were masked to the measurements of their colleagues. The subjects measured were referrals to the eye plastic and orbital service over a three week interval. Substantial interobserver variation was demonstrated. Fully one-fourth to one-third of all measurements by the three less-experienced observers differed enough from the senior observer to be of concern to him. The direction of disagreement varied with experience. The least-experienced observer consistently underread whereas the more experienced observer slightly overread exophthalmometry, relative to the senior observer. As the study progressed, the least-experienced observer's reliability increased. Interobserver agreement for this observer was influenced by the degree of proptosis presenting in the eye being measured.