We sought to investigate the shared use of core Ophthalmology terms in the domains of Ophthalmology, Family Practice and Radiology. A random sample of 450 terms was selected from the terms submitted as Ophthalmology terms in the NLM/AHCPR Large Scale Vocabulary Test. Two expert Ophthalmologists rated each term as Ophthalmic or non-Ophthalmic. When both raters agreed that a term was Ophthalmic, it was treated as a core Ophthalmology term for purposes of the study. We searched for the core terms in a text corpus of 38,695 MEDLINE abstracts covering 1970-1999 from journals representing the three domains of Ophthalmology, Radiology, and Family Practice. We compared proportions of abstracts from each domain for each term. We examined overlap of confidence intervals for proportions of abstracts for each core term and domain. Core Ophthalmology terms were used significantly more by Ophthalmology than by Radiology, or by Family Practice.