A 25 year – old female gives a history of redness, pain and mild diminution of vision in one eye for past 3 days . There is also a history of low backache for the past one year. On examination there is circumcorneal congestion, cornea is clear apa from a few fine keratic precipitates on the corneal endothelium, there are 2+ cells in the anterior chamber, anterior chamber depth being normal and the intraocular pressure is within normal limits. The patient is most likely suffering from :

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