Fuchs Uveitis Syndrome (FUS)

Also called Fuchs heterochromic iridocyclitis (FHC) or Fuchs heterochromic cyclitis. A classic and well-characterised chronic anterior uveitis entity.

Overview

Type: Chronic, non-granulomatous anterior uveitis
Age at diagnosis: Average ~40 years
Sex/race: No predilection
Laterality: Unilateral in 90-95% of cases
Etiology: Uncertain. Strongest evidence implicates rubella virus. Toxoplasma gondii has also been suspected. Much of the apparent "anterior chamber (AC) activity" may be due to blood-aqueous barrier breakdown rather than true inflammation.

Clinical Features

Symptoms

Often detected incidentally
Gradual visual blurring (due to cataract development)
Persistent floaters
Patient or clinician may notice heterochromia

Signs (the "FUS constellation")

1. Heterochromia iridis

Most effectively seen in daylight
Typically the affected eye is hypochromic (lighter) - Fig. A below
Due to diffuse iris stromal atrophy + posterior pigment epithelial atrophy
Exception: in blue eyes, stromal atrophy allows the pigmented posterior layer to dominate, making the eye paradoxically hyperchromic

Fig. 12.13A - Right eye involvement showing hypochromia (lighter right iris vs. darker left)

2. Keratic precipitates (KPs)

Characteristically stellate, grey-white
Located diffusely over the entire corneal endothelium (not just inferior as in typical uveitis)
This diffuse stellate distribution is pathognomonic

Fig. 12.13B - Diffuse stellate keratic precipitates distributed across entire endothelium

3. Iris nodules

Koeppe nodules (on pupillary border) - present in ~30% - arrow shown in Fig. C
Russell bodies (tiny crystals) may be present on iris surface

Fig. 12.13C - Koeppe nodules (arrow) at pupillary border with iris atrophy and loss of stromal architecture

4. Iris atrophy

Diffuse with loss of crypts
Iris appears smooth with a prominent sphincter pupillae
Pigment epithelial atrophy demonstrated by retroillumination (band-like pattern)
Fine irregular iris surface vessels commonly present

5. Anterior chamber

Faint flare, usually only mild cellular activity
The eye is virtually always white even during exacerbations - no ciliary injection
No posterior synechiae (PS) - absence of PS is a distinguishing feature (may appear post-surgery)

6. Vitritis

Anterior vitreous opacities may be dense

7. Posterior subcapsular cataract

Extremely common - a frequent mode of presentation

8. Glaucoma

A later manifestation, but occasionally present at diagnosis
Develops in up to 60% of involved eyes
Multiple mechanisms suspected

9. Gonioscopy

Fine radial angle vessels or small irregular peripheral anterior synechiae (PAS)
These angle vessels are the source of the Amsler sign - a small hyphema that appears on paracentesis / AC incision due to bleeding from fragile neovascular angle vessels

10. Fundus

Peripheral choroiditis foci/scarring reported
Possible increased incidence of retinal dialysis
Macular edema does not occur except following surgery (a key differentiator)

Heterochromia Iridis - Differential Diagnosis

Type	Causes
Hypochromic (lighter)	Idiopathic congenital, Horner syndrome (especially congenital), Waardenburg syndrome
Hyperchromic (darker)	Topical prostaglandin analogue use, oculodermal melanocytosis (naevus of Ota), ocular siderosis, diffuse iris naevus/melanoma, Sturge-Weber syndrome
Either	Fuchs uveitis syndrome, other chronic anterior uveitides

Investigation

Diagnosis is clinical. Investigation is needed only to exclude alternative conditions (e.g., herpetic uveitis, sarcoidosis, toxoplasmosis).

Treatment

Problem	Management
Chronic low-grade inflammation	Topical steroids generally NOT helpful long-term; may be used short-term for moderate/severe exacerbations
Monitoring	Long-term monitoring for glaucoma and cataract is mandatory
Cataract surgery	Carries increased risk: poor mydriasis, postoperative hyphema, increased inflammation, worsened glaucoma, zonular dehiscence. Preoperative topical/systemic steroids used by some
Glaucoma	Often difficult to control medically; surgical options include glaucoma drainage device or trabeculectomy + mitomycin-C
Vitreous opacification	Pars plana vitrectomy may be considered for visually significant cases

Key Points for Exam / Clinic

FUS is almost always unilateral, presents in middle age, no sex preference
The eye is white and quiet-looking despite active inflammation
No posterior synechiae (absence is hallmark - unlike most other anterior uveitides)
KPs are diffuse and stellate (not inferior/mutton-fat)
Amsler sign - bleeding from angle vessels during paracentesis
Macular edema absent (except post-op)
Rubella virus is the leading suspected etiology
Glaucoma develops in up to 60% - the most significant long-term complication
Steroids do NOT prevent progression and are not used chronically

Source: Kanski's Clinical Ophthalmology: A Systematic Approach, 10th edition, p. 459-460

This is a shared conversation. Sign in to Orris to start your own chat.