PURPOSE: This study was designed to assess the new clinical information given by optical coherence tomography in patients with idiopathic macular hole. METHODS: Sixty-one consecutive eyes of 47 patients with idiopathic macular hole at different stages of development were studied clinically. Patients with myopia, epiretinal macular membrane, and any other ocular disc ease were excluded. Best-refracted visual acuity and biomicroscopic fundus examination with macular contact lens were performed. Optical coherence tomography was performed through a dilated pupil. The optical coherence tomography findings were correlated with the Gass biomicroscopic classification of idiopathic macular hole. RESULTS: Optical coherence tomography provided different or additional information in 22 of 24 eyes (91.7%) biomicroscopically classified in stages 1-A and stage 1-B according to the Gass macular hole classification, and in seven of 37 eyes (18.9%) biomicroscopically classified in stages 2, 3, and 4. The main difference from Gass biomicroscopic classification was a macular pseudocyst instead of a foveolar detachment in the first stages. The main additional optical coherence tomography observation, not detected biomicroscopically, was the presence of retinal tissue on the bottom of the macular hole. Optical coherence tomography may be particularly useful in evaluation of early stages in development of idiopathic macular hole. CONCLUSIONS: Compared with classic biomicroscopical observation, optical coherence tomography frequently gives different or additional information on idiopathic macular hole, especially in its early stages. Correct diagnosis and surgical indication of idiopathic macular hole may benefit from optical coherence tomography imaging. (Am J Ophthalmol 2001;132:348-355. (C) 2001 by Elsevier Science Inc. All rights reserved.).