Eyes, Ears, Nose and Throat practice

A 78-year-old woman presents with sudden painless loss of vision in her right eye on waking this morning. For the past three weeks she has had a right-sided headache, soreness of the scalp when brushing her hair, and an ache in her jaw muscles that comes on while chewing tough meat and settles when she rests. Visual acuity in the right eye is hand movements only, with a right relative afferent pupillary defect, and the right optic disc is swollen and pale. Her ESR is 98 mm/h (<20) and C-reactive protein is 84 mg/L (<5). Which one of the following is the most appropriate immediate management?