Background: The activity of thyroid orbitopathy can be evaluated with CAS (Clinical Activity Score) based on 7 inflammatory signs. Selenium acts as an oxide-reducing agent in thioredoxin-reductase, and as an anti-inflammatory agent by reducing the hydroxy peroxide intermediates on the cyclo-oxygenase pathways. Increased oxidative stress has been observed in Graves' disease and therefore, by incorporating an antioxidant such as selenium in patients with mild thyroid ophthalmopathy, inflammatory activity could be reduced or inactivated.

General Objective: To determine the clinical differences between patients with mild thyroid orbitopathy who were administered oral supplementation with selenium and patients who were administered oral placebo.

This is a simple controlled clinical trial. In which 66 eyes of 33 patients were studied. Fifteen patients were assigned to the placebo group and 18 to the Selenium group. We randomized into two groups the patients with mild clinical activity according to CAS score. Group A took placebo pills twice a day which consisted in 100µg of starch, and Group B took a pill of Selenium 100 µg twice a day. All the subjects tool the pills during six months. Patients of both groups where examined and evaluated with CAS score before and after the first, third and sixth month of treatment.

Inclusion Criteria:

• Patients with active mild thyroid orbitopathy according to CAS scale.
• Older than 18 years of age.

Exclusion Criteria:

• Patients with mild thyroid orbitopathy undergoing treatment with corticosteroids.
• Active smokers
• Patients allergic to Selenium
• Follow-up shorter than 6 months