GO was diagnosed in the Department of Endocrinology and/or the Department of Ophthalmology based on the clinical and laboratory findings. According to the European Group on Graves' Orbitopathy (EUGOGO), the enrolled patients were classified as having mild, moderate, or severe orbital disease. Mild disease was defined as minimal soft tissue swelling, minor lid retraction (<2 mm), exophthalmos <3 mm above normal for race and gender, no or intermittent diplopia, and corneal exposure responsive to lubricants. Moderate-to-severe GO was defined as marked soft tissue swelling, and/or exophthalmos of 3 mm or more above normal for race and gender, and/or lid retraction of 2 mm or more, and/or intermittent or constant diplopia but no optic nerve involvement. Sight-threatening eye disease was defined as optic nerve involvement (dysthyroid optic neuropathy) and/or corneal breakdown. If no alternative causes of visual impairment were identified, patients with the following conditions were considered to have dysthyroid optic neuropathy
15 characterized by abnormal visual acuity (VA) associated with changes in the visual field examination compatible with optic neuropathy, a relative afferent pupillary defect, and/or impaired color vision. The presence of apical crowding on coronal computed tomography (CT) scans supported this diagnosis. Disease activity was evaluated using the clinical activity score.
1 Patients with a clinical activity score of 3 or higher initially can expect beneficial effects from nonsurgical therapy and were not included in this study. Patients who had had an ocular surgery, had been treated with iodine 131, or had received steroid treatment during the last 6 months were also excluded. Orbits included were further subdivided into two groups: one with predominantly lipogenic disease and one with predominantly myogenic disease, corresponding respectively to type I and type II orbitopathy in Nunery′s classification.
16 Basic clinical data including age, gender, smoking habit, disease duration, and history of steroid treatment and/or radiotherapy were recorded. A full ophthalmic examination including pupillary responses, best-corrected VA (BCVA), biomicroscopic evaluation of the anterior and posterior poles, Goldmann applanation tonometry, standard automated perimetry with the Swedish Interactive Threshold Algorithm 24 to 4 strategy, and optical coherence tomography (OCT) scanning of the optic nerve head were performed preoperatively and one month postoperatively. Axial proptosis was measured using Hertel exophthalmometry, and the presence of diplopia was recorded and measured with the alternate prism-and-cover test preoperatively and postoperatively. CT examinations of all patients were performed preoperatively with a high-resolution scanner (multidetector CT; Philips and Samsung, Madrid, Spain), and muscle enlargement was measured and interpreted based on the published normative CT data for orbital structures.
17 Muscle index determined by adding the diameters of medial rectus muscle, lateral rectus muscle, inferior rectus muscle and superior rectus-levator palpebra superior group was calculated.