Subclinical visual field alterations are commonly present in patients with Graves' Orbitopathy and are mainly related to the clinical activity of the disease.

The present study was aimed to investigate optic nerve involvement by computerized perimetry in 40 (29 women, 11 men) consecutive GO patients not showing definite dysthyroid optic neuropathy (DON). All patients presenting visual acuity defects, pallor or swelling of the optic nerve, concomitant eye disease, evidence of apical crowding or optic nerve stretching at either MRI or CT imaging were excluded. Normal perimetry occurred in 7 patients (17.5%), 5 patients (12.5%) had "indeterminate" results and 28 patients (70%) presented abnormal perimetry. Particularly, 7 isolated paracentral, 5 pericentral and 16 combined peri and paracentral scotomas were found. On the contrary, 15/20 patients in the group without GO had normal perimetry, isolated scotomas were found in 5 cases (1 pericentral and 4 paracentral) and no case of combined scotoma occurred. The difference between the 2 groups was statistically significant (x2 = 9.17; p = 0.025). Overall, the sensitivity resulted 70%, the specificity 75% and the positive predictive value 84.8%. In patients with GO, the proportion of visual field alterations was significantly increased for Clinical Activity Score > or = 3 (p = 0.0005), while no relationship occurred with proptosis degree (p = 0.115). In conclusion, a great proportion of GO patients without clinically evident DON presents visual field defects, mainly related to GO activity.