Characterizing ethambutol‐induced optic neuropathy with a 3D computer‐automated threshold Amsler grid test

metastases into consideration, palliative surgery to preserve vision in the only eye was performed. The lateral mid-facial approach included osteotomy of the lateral orbital wall and the zygoma. Upon opening the periorbit, the brown tumour infiltrating the muscle was visible. The optic nerve and its nutritive vessels were completely preserved. The lateral rectus tendon was then severed through a limbal incision. After subtotal removal of the metastasis and the rectus superior muscle, a straight position of the eye was restored using a 1-mm silicone tube. Through two burr holes, this tube was fixed to the lateral orbital wall. The tube was then threaded through the empty pulley, that is, the hole in Tenon’s capsule, which remained after the lateral rectus muscle was removed. The tube was sutured to the former insertion site of the lateral rectus muscle (Fig. 3). In this way the globe was positioned in an abduction of approximately 5°. After surgery, chemosis rapidly disappeared and visual acuity recovered up to 0.63 within 2 weeks. The visual field was not impaired. Upgaze was reduced to 15°, abduction to 5°; and adduction was possible up to 10°. The histopathological findings verified the diagnosis of a malignant melanoma, which correlates to the primary tumour. Systemic metastases of choroidal melanoma predominantly appear in the liver. Lung, bone, skin and lymph nodes are often involved, mostly in patients with liver metastases. Our patient also had liver, lung and lymph node metastases before the orbital metastasis. Metastatic melanoma of the orbit, in contrast to recurrence of a melanoma in the ipsilateral orbit due to extrascleral seeding of the tumour, develops in the terminal stages of the disease. The life expectancy of the patient is short, and therefore treatment should be palliative. Radiotherapy is an accepted treatment for intraocular tumours. In literature, radiotherapy is described as a treatment for similar cases with bilateral choroidal melanoma. In our patient, we decided to decompress the optic nerve by removing the tumour. A xenotransplant was used to reposition the eye. We applied a method similar to the one described by Kolling for treatment of 6th nerve palsy, and comparable to the recently described periosteal anchor of the medial rectus for treatment of 3rd nerve palsy. Hummelsheim transposition was discussed as an alternative. This would, however, have included a significant risk of ischaemia in our case, owing to the interruption of anterior ciliary vessels of three neighbouring rectus muscles.