The present study compares contrast sensitivity functions of patients with uncomplicated Graves' ophthalmopathy, patients with ophthalmopathy and elevated intraocular pressure or suspect glaucoma, and patients with dysthyroid optic neuropathy (DON). Aim of the study was to investigate the clinical potential for the contrast sensitivity functions (CSF) in distinguish between the groups. Contrast sensitivity measurements were obtained from twenty-seven subjects with endocrine ophthalmopathy. Group I included patients with uncomplicated ophthalmopathy (n=20 eyes); group II included patients with ophthalmopathy, intraocular pressure > or = 24 mmHg with and without early visual field defects, and no evidence of apical crowding on coronal computed tomography scan (n=14 eyes); group III included patients with DON (n=12 eyes). Contrast thresholds were determined for stationary and 6.87 Hz phase-alternating gratings at eight spatial frequencies from 0.18 to 15.7 c/deg. Data from each group was compared with data from age-matched normal subjects. Observers with uncomplicated ophthalmopathy had normal CSFs. Eyes affected with DON showed contrast sensitivity disruption at overall intermediate-high spatial frequencies. Eyes with elevated intraocular pressure or suspect glaucoma had pronounced sensitivity loss in the low frequency range (0.18-0.70 c/deg) as compared to eyes with DON. This study shows that CSF detects visual function abnormalities noninvasively in patients with complicated Graves' ophthalmopathy. Results also indicate that the clinical potential for CSF in distinguish between patients suffering from ophthalmopathy complicated by ocular hypertension or suspect glaucoma and patients with DON improves when a temporal modulation of 6.87 Hz and gratings of low spatial frequency (< 1 c/deg) are used.