“B27” iritis

50% of people who suffer from iritis are positive for a blood test which looks for a factor called “HLA-B27”.  Your doctor may diagnose you as having B27 associated iritis by your symptoms and course. This diagnosis may be confirmed by the B27 blood test.

If you have B27 it means you have a statistically higher chance of developing the symptoms of other B27-associated diseases. Some people feel that they would like to know if they are thus predisposed.  Some people think that there is no point in knowing, because the other conditions cannot be prevented from happening. It is estimated that 80% of people with B27 have no illnesses linked to B27.

B27 associated diseases include

Iritis (anterior uveitis)

Ankylosing spondylitis


Crohn’s disease

Ulcerative colitis

Reiter’s syndrome

Features of B27 associated iritis

Unilateral (affects one eye at a time)


Each attack lasts 2-6 weeks on average

In some cases one eye may develop iritis followed by the other a week later

Some cases become chronic and require a small dose of steroid (eg twice weekly) to prevent frequent flare-ups

Treatment of B27 associated iritis

Dilation of pupil to prevent iris from sticking to lens (eg. Cyclopentolate [Mydrilate] or Atropine)

Frequent topical steroids (eg. Prednisolone [PredForte] or Dexamethasone [Maxidex]) – often initially hourly then tapered off week by week. Beclomethasone [Betnesol] ointment may be prescribed for use at night

What is HLA-B27?  If I've got it, what can I do about it?

It is something you inherit, like green eyes or blonde hair: there is nothing you can do about it.  In the United States, 6-8% of the Caucasian population is B27 positive. It is more common in certain ethnic groups, such as Finns and Native Americans, and uncommon in others, such as Black Americans, Africans and Japanese.

What does the "HLA" mean?

It stands for "Human Leukocyte Antigen". A leukocyte is a kind of white blood cell. An antigen is a kind of protein found on the surface of the cell. HLA's are what the body's immune system uses to keep track of "self" and "non-self". It is thought that the cause of iritis (and other "auto-immune") diseases is that the body gets "self" and "non-self" confused.

Further information of a technical nature can be found here (this information was intended for ophthalmologists).

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