A 30-year-old anxious woman presented to the outpatient department as she noticed grittiness and redness in her eyes. She says that her husband noticed her to be having a staring look, and she too feels that her left eye appears to be more protruding than the right eye. Since the last few days, she has also noticed diplopia on seeing upwards, and her vision has dropped significantly in her left eye. Examination showed visual acuity in her left was counting fingers 3 meters, there was lid retraction, severe conjunctival congestion, restriction of extraocular movements, and a 3mm proptosis. Pupillary examination revealed the presence of RAPD (relative afferent pupillary defect). The most important concern of the ophthalmologists in this patient that requires emergency intravenous steroids to save her vision is:

a) Optic neuritis
b) Thyroid eye disease
c) Ocular myasthenia
d) Orbital cellulitis