Flashing lights in thyroid eye disease: a new symptom described and (possibly) explained

Some patients with restrictive thyroid ophthalmopathy, referred for consideration of extraocular muscle surgery, complained of flashing lights in the superior visual field on upgaze. The frequency was assessed and the pathogenesis of this previously unreported symptom explored.

30 patients were recruited, all of whom had tight inferior recti and were in the burnt out phase of thyroid eye disease. They were directly questioned regarding any symptoms of photopsia and their records were examined with respect to disease status and treatment, ocular motility, intraocular pressure, retinal status, and surgical intervention. Magnetic resonance imaging (MRI) and cine MRI scans were reviewed for evidence of globe compression. The frequency of symptoms was compared with an age and sex matched control group.

Three patients spontaneously complained of flashing lights. A further nine patients had this symptom when directly questioned. 18 patients had no symptoms. None of the 33 control patients had symptoms on direct questioning. Sagittal MRI and cine MRI failed to demonstrate globe compression by the inferior rectus muscle even in cases that showed an intraocular pressure rise in upgaze.

A new symptom of flashing lights in upgaze has been identified in thyroid eye disease patients with tight inferior recti. It is suggested that the lights are likely to be phosphenes as a result of either compression of the globe by a tight inferior rectus or traction on the insertion of the inferior rectus. The small amount of globe compression required to produce phosphenes seems to be beyond the resolution limit of MRI.