MSRA-1646

A 30-year-old male with a history of ankylosing spondylitis presents to his GP with complaints of eye pain and sensitivity to light. He wears glasses for nearsightedness and this is his first occurrence, affecting only his right eye. Upon examination, his right eye has a visual acuity of 6/6 while his left eye is corrected to 6/18. The left pupil is misshapen and the eye is red, but the cornea appears clear. What is the most likely diagnosis for this patient?