A 9-year-old boy presented with a one-year history of several episodes of erythema and increased sweating on the right side of his face that appeared immediately after intense physical exercise. The skin findings were not present at the time of consultation. A photograph of one of the episodes was provided by the parent showing right hemifacial erythema (Figure 1). Physical examination, however, revealed contralateral anisocoria, miosis, mild hypochromia of the iris, ptosis measuring approximately 2 mm, as well as slight enophthalmos of the left eye ( Figure 2). These ocular features were permanent and had been present since birth. What is the diagnosis?