What is the most common cause of acute unilateral (or alternating) anterior non-granulomatous uveitis?

The most common cause of acute unilateral or alternating anterior non-granulomatous uveitis is ankylosing spondylitis. This condition is part of a group of inflammatory diseases known as spondyloarthritis, which is characterized by axial skeleton involvement and often presents with associated ocular manifestations, particularly uveitis. In cases of ankylosing spondylitis, uveitis can manifest as an acute episode of eye redness and pain, with the potential for recurrence.

The relationship between ankylosing spondylitis and anterior uveitis is particularly strong due to the associations between HLA-B27 positivity and the presence of uveitis in these patients. Although other systemic conditions can cause uveitis, the unique characteristics of ankylosing spondylitis make it the most prevalent cause in acute unilateral cases.

Rheumatoid arthritis and psoriatic arthritis can cause uveitis, but they are less commonly linked to acute anterior uveitis compared to ankylosing spondylitis. Sarcoidosis is known for causing granulomatous uveitis and is less likely to present with the specific acute non-granulomatous form. Thus, the predominance of ankylosing spondyl