RAPD as a clinical alert for early evidence of dysthyroid optic neuropathy

Dysthyroid optic neuropathy (DON) is a serious manifestation of thyroid eye disease (TED) resulting in permanent visual loss. There is controversy regarding the diagnostic features of DON. Relative afferent pupil defect (RAPD) in TED is highly specific for DON. Our first patient, a 42-year-old male presented with proptosis and intermittent blurring of vision with best corrected visual acuity of 6/6 in both eyes and right RAPD as an early sign of DON. Our second patient, a 54-year-old female presented with proptosis and clinical activity score <3 at the time of presentation. She developed intermittent blurring of vision with left RAPD on her second presentation as clue of bilateral asymmetric DON in her eyes, though BCVA was 6/6 both eyes. Both cases of bilateral asymmetric DON had RAPD as early specific sign of DON, which prompted us to do detailed radio-imaging to confirm DON, hence highlighting the importance of RAPD.