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Diseases of the Iris

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1. Congenital Anomalies

Aniridia

• AD form (~2/3 of cases): no systemic implications; complete penetrance, variable expressivity
• Sporadic/WAGR syndrome (~1/3): previously "Miller syndrome" - Wilms tumour, Aniridia, Genito-urinary abnormalities, mental Retardation. ~30% chance of Wilms tumour
• Gillespie syndrome (~1%): AR (not PAX6), cerebellar ataxia + learning disabilities
• Presentation: nystagmus, photophobia at birth; apparent "large pupils" (absent iris)
• Ocular features: limbal stem cell deficiency, corneal vascularization, cataract, lens subluxation, foveal/optic nerve hypoplasia
• Glaucoma (75%): late childhood/adolescence, due to synechial angle closure from rudimentary iris contraction
• Monitoring: abdominal ultrasound every 3 months until age 5 (then 6-monthly to age 10, annually to 16) for Wilms tumour unless WT1 mutation excluded

Iris Coloboma

• Results from failed closure of the embryonic fissure (inferior)
• Appears as a keyhole-shaped inferior pupil defect
• May be associated with choroidal/retinal coloboma
• Can occur in isolation or as part of CHARGE syndrome

Congenital Ectropion Uveae

• Uncommon; displacement of posterior pigmented epithelium onto the anterior iris surface
• May be associated with glaucoma

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2. Inflammatory Diseases

Anterior Uveitis (Iritis / Iridocyclitis)

• Acute: pain, redness, photophobia, consensual photophobia, tearing, decreased vision
• Chronic: reduced vision (cataract, CME, ERM), floaters; minimal pain (e.g., JIA-associated)

• Cells and flare in the anterior chamber (graded 0-4+)
• Ciliary flush (perilimbal injection)
• Keratic precipitates (KP):

• Posterior synechiae (iris-to-lens adhesions), iris nodules, hypopyon (HLA-B27, Behçet)
• IOP: usually low (ciliary hyposecretion); raised in herpetic, Fuchs, Posner-Schlossman

• Topical corticosteroids (prednisolone acetate 1%)
• Cycloplegic agents (atropine, cyclopentolate) to prevent synechiae and relieve spasm
• Periocular/systemic steroids for severe or refractory cases
• Treat underlying cause

Fuchs Uveitis Syndrome (Fuchs Heterochromic Iridocyclitis - FHC/FUS)

• Chronic, low-grade, non-granulomatous uveitis; mean age 40 years
• Typically unilateral, more common in middle-aged women
• Characterized by: diffuse fine KP (stellate), loss of iris pigment epithelium causing heterochromia (affected eye is lighter), fine bridging vessels in the angle (bleed on paracentesis - Amsler sign)
• Complications: cataract (very common), secondary glaucoma
• Associated with CMV or rubella virus in many cases
• No synechiae (distinguishing feature)

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3. Iris Tumours

Iris Naevus

• Circumscribed solitary flat or variably elevated pigmented lesion in the superficial stroma
• Disrupts normal iris architecture
• Diffuse naevus: occurs in congenital ocular melanocytosis and Cogan-Reese (ICE) syndrome
• Malignant transformation rate: up to 8% over 15 years
• Risk factors for malignancy: age <40, inferior location, bleeding, diffuse involvement, feathery margins, ectropion uveae
• Management: lifelong observation with slit lamp photography

Iris Freckle (Ephelis)

• Superficial, flat; no elevation or distortion of iris architecture
• Increased melanocyte pigmentation but normal cell number
• No malignant potential

Brushfield Spots

• Small whitish peripheral iris speckles in a concentric ring
• Classically associated with Down syndrome (trisomy 21), also normal in blue eyes
• Consist of focal hyperplasia surrounded by a ring of hypoplasia
• No malignant potential

Lisch Nodules

• Small well-defined bilateral iris nodules
• Pathognomonic of neurofibromatosis type 1 (NF1); present in >95% by second-third decade
• Hamartomas; no malignant potential

Iris Melanoma

• ~8% of all uveal melanomas; better prognosis than choroidal melanoma (~5% metastasis at 10 years)
• Risk factors: fair skin, light iris colour, atypical naevi, ocular melanocytosis, chronic UV/arc welding exposure
• Presentation: middle age (a decade earlier than choroidal melanoma); enlargement of pre-existing naevus
• Histology: diffusely infiltrating spindle cells (low-grade); epithelioid component = more aggressive
• Signs:
  • Pigmented nodule ≥3 mm diameter, ≥1 mm thick, typically inferior half of iris
  • Prominent surface blood vessels
  • Pupillary distortion, ectropion uveae, localized cataract
  • Rarely amelanotic
  • Angle infiltration possible; extrascleral extension rare
• Complications: hyphaema, cataract, glaucoma
• Investigations: UBM (to rule out ciliary body involvement), fine-needle aspiration biopsy, systemic staging
• Treatment:
  • Sector iridectomy (small tumours)
  • Iridocyclectomy (angle involvement)
  • Brachytherapy or proton beam radiotherapy
  • Enucleation for diffuse tumours

Metastatic Tumours to the Iris

• Rare; fast-growing white/pink/yellow masses
• Associated with anterior uveitis and occasionally hyphaema
• Primary sites: breast, lung, cutaneous melanoma (most common)

Juvenile Xanthogranuloma (JXG)

• Rare idiopathic granulomatous disease of early childhood
• Iris involvement can cause spontaneous hyphaema - key clinical clue
• Yellow-orange lesions on iris
• Treated with topical/systemic steroids

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4. Iris Cysts

Primary Epithelial Cysts

• Arise from iris/iridociliary pigment epithelium
• 75% peripheral iris - smooth dome-shaped bulging visible on gonioscopy
• May rarely dislodge to float freely in AC or vitreous
• Most are asymptomatic; large cysts causing vision obstruction treated with focal photocoagulation

Primary Stromal Cysts

• Solitary, unilateral, smooth translucent anterior wall on or within iris
• Congenital type (more aggressive): requires aspiration, surgical excision, or ethanol sclerosis
• May remain stable for years, then enlarge or spontaneously rupture

Secondary Cysts

• Traumatic: conjunctival/corneal epithelial implantation after penetrating injury or surgery; frequently enlarge, causing corneal oedema, uveitis, and glaucoma
• Miotic-induced: long-acting miotic drugs (e.g., echothiophate) cause bilateral, multiple small pupillary border cysts; prevented by concurrent phenylephrine 2.5%
• Parasitic: extremely rare

Anterior segment OCT and ultrasound biomicroscopy (UBM) are key tools to differentiate iris cysts from solid ciliary body tumours.

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5. Iris Heterochromia

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6. Iris Lesion Classification (Wills Eye)

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7. Iris Neovascularization (Rubeosis Iridis)

• Diabetic retinopathy (most common)
• Ocular ischemic syndrome
• Central or branch retinal vein/artery occlusion
• Chronic uveitis, chronic retinal detachment
• Intraocular tumours (retinoblastoma, melanoma)

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