Iritis

Overview

Inflammation of the iris/anterior uveal tract - the most common form of uveitis (~75-90% of cases). Most commonly affects adults aged 30-40. ~50% are HLA-B27 positive.

Aetiology

•Idiopathic - most common single category

•HLA-B27-associated - ankylosing spondylitis (most common systemic association), reactive arthritis, psoriatic arthritis, IBD-related arthritis

•Sarcoidosis - granulomatous uveitis with large 'mutton-fat' keratic precipitates

•Behçet's disease - recurrent hypopyon uveitis

•JIA - children; often asymptomatic, detected on screening

•Infectious - HSV, VZV (most common viral); syphilis must be excluded in all cases; TB

💡

In a first episode of iritis, always ask about back pain, joint disease, skin rashes, and bowel symptoms - you may be making the first diagnosis of ankylosing spondylitis or IBD.

Presentation

•Deep, aching ocular pain - from ciliary spasm; worsened by bright light

•Photophobia - often severe; ciliary muscle spasm triggered by pupillary movement

•Blurred vision - cells and protein in anterior chamber

•Perilimbal (ciliary) flush - ring of deep redness around cornea; distinguishes from conjunctivitis

•Small, irregular, poorly reactive pupil - iris sphincter spasm; posterior synechiae cause irregular outline

•Watery lacrimation - not purulent

•Hypopyon - visible layer of white cells in inferior anterior chamber; severe cases; associated with Behçet's and HLA-B27 disease

Investigations

🏆 Gold standard

•slit-lamp biomicroscopy - anterior chamber cells, flare (Tyndall effect/'headlight in fog'), keratic precipitates, posterior synechiae

🥇 First-line

•intraocular pressure measurement; dilated fundus examination; HLA-B27 typing; FBC, ESR, CRP; syphilis serology (TPHA/VDRL) - must be excluded in all new cases

🥈 Second-line

•CXR (sarcoidosis/TB); ACE and serum calcium (sarcoidosis); ANA, rheumatoid factor (JIA); HSV/VZV PCR from aqueous tap (herpetic aetiology)

Management

•All patients require same-day urgent ophthalmology referral - do not manage in primary care alone

🥇 First-line

•topical corticosteroid - prednisolone acetate 1% or dexamethasone 0.1% eye drops (hourly initially, then tapered)

•cycloplegic - cyclopentolate 1% eye drops - paralyses ciliary muscle (relieves spasm pain), dilates pupil (prevents/breaks posterior synechiae)

🥈 Second-line

•oral prednisolone - severe disease not controlled by topical therapy, or bilateral disease

•periocular corticosteroid injection - subtenon triamcinolone for severe/refractory cases

🥉 Third-line

•systemic immunosuppression - methotrexate, azathioprine, or mycophenolate mofetil for chronic/recurrent/steroid-dependent disease

•If infectious: aciclovir (oral/topical) for herpetic disease; do not use topical steroids alone if HSV keratouveitis suspected without antiviral cover

💡

Cycloplegics relieve pain by mechanism: paralysing the ciliary muscle with cyclopentolate removes the spasm that is the primary pain source - not just symptom masking. Expected blurred vision from dilation is temporary.

Complications

•Posterior synechiae - iris adheres to lens; circumferential adhesion causes iris bombé → acute secondary angle closure glaucoma

•Secondary glaucoma - trabecular blockage by debris, trabeculitis, or pupillary block; risk of irreversible optic nerve damage

•Cataract - chronic inflammation and prolonged corticosteroid use → posterior subcapsular cataract

•Cystoid macular oedema (CMO) - most common cause of visual loss in uveitis

•Band keratopathy - calcium deposits in Bowman's layer; associated with chronic/recurrent anterior uveitis, particularly JIA

•Hypotony - chronic ciliary body inflammation → reduced aqueous production → phthisis bulbi in severe end-stage disease

Prognosis

•Single acute idiopathic/HLA-B27 episode: good prognosis with prompt treatment - resolves within 6-8 weeks

•Recurrence is common in HLA-B27-positive individuals; each episode risks cumulative structural damage

•Granulomatous forms (e.g. sarcoidosis) carry higher risk of permanent visual impairment than acute non-granulomatous disease

Differential Diagnosis - Red Eye

Distinguishing causes of the red eye

Feature	Iritis	Conjunctivitis	Acute angle closure glaucoma
Pain	Deep, aching	Mild/none	Severe
Photophobia	Yes - severe	No	Yes
Pupil	Small, irregular	Normal	Mid-dilated, fixed
IOP	Low or raised	Normal	Markedly raised
Discharge	Watery	Purulent/mucopurulent	None
Redness	Perilimbal (ciliary flush)	Diffuse/follicular	Diffuse

🚨

Never send a patient with a painful red eye home without measuring intraocular pressure. Acute angle closure glaucoma - mid-dilated fixed pupil, rock-hard eye, markedly raised IOP - is a sight-threatening emergency requiring immediate ophthalmology review.