Vitreal seeding from uveal melanoma detected by high-resolution spectral-domain optical coherence tomography.

Comment. Episcleral neurofibromas and schwannomas likely arise from the long posterior ciliary nerves within the sclera. The ciliary nerves pierce the sclera near the optic nerve and pass anteriorly within the sclera and suprachoroidal space while branching to form a loose connection between the long and short posterior ciliary nerves, leading to 20 to 30 branches at the level of the ciliary body. The nerve loop of Axenfeld is an anastomotic interconnection of the long ciliary nerve that occasionally turns to enter the sclera before turning back again to continue anteriorly to the ciliary body. The loops occur in the area 2 to 4 mm posterior to the limbus, and no loops occur in the zones directly anterior to the medial and lateral rectus tendons. Anterior episcleral nerve sheath tumors have a topographicdistributionsimilar to theAxenfeldnerve loop,permittingspeculationof their relationship.Thedistances from the center of the tumor to the limbus narrowly ranged from 3 to 4 mm. None of these tumors occurred directly anterior to the horizontal rectus muscle tendons (Table). The anterior tumors were evenly distributed among the remaining quadrants as described for Axenfeld nerve loops. Two of4episcleral schwannomasoccurredintheposteriorsclera. If the distribution were random in the ciliary nerves, then some tumors would be expected to be found in the horizontalplaneandatmorevariabledistances fromthe limbus. The apex of the loop can extend through the full thickness of the sclera and project above the scleral surface. Pain and tenderness have been noted when the nerve loops are located anteriorly. The sharp bend in the nerve and the ensuing stress perhaps facilitate the abnormal proliferation of nerve sheath cells and the formation of these tumors. The differential diagnosis for all of the reported episcleral nerve sheath tumors includes solitary circumscribed neuroma, but as in our case the published cases lack sufficient encapsulation to warrant this diagnosis.