The purpose of this study was to demonstrate microstructural differences be
tween clinically similar, but aetiologically different, cases of corneal oe
dema in four subjects. In vivo confocal microscopy highlighted oedema of th
e basal epithelium, prominent nerve-keratocyte interactions, and typical 'e
pithelialization' of the endothelium in a case of iridocorneal endothelial
syndrome; however, a similar microstructural appearance was observed in a c
ase of presumed herpetic disciform keratitis. The latter diagnosis was subs
equently revised on this basis. Confocal examination of Fuchs' endothelial
dystrophy demonstrated oedema of the basal epithelium, prominent wing cells
, anterior stromal alterations, fibrosis of Descemet's membrane and a typic
al 'strawberry' appearance of the endothelium. In contrast, in vivo microst
ructural examination of bilateral keratoconus with hydrops confirmed oedema
mainly involving the epithelium and anterior stroma. In vivo confocal micr
oscopy allows the clinician to observe the living cornea at a microstructur
al level and to better diagnose and differentiate borderline or unusual cas
es of corneal oedema.