Fuchs heterochromic iridocyclitis is an ocular condition characterized by the presence of keratic precipitates, iris heterochromia and iris atrophy.
What is Fuchs Heterochromic Iridocyclitis?
Fuchs heterochromic iridocyclitis (FHI) is one of the most common types of anterior uveitis and is thought to account for approximately 8% of all cases of endogenous uveitis. The condition was first coined by Ernst Fuchs in the early twentieth century who investigated the pathological and clinical features consistently seen in individuals with cataract, heterochromia and chronic low-grade anterior chamber inflammation.
Etiology of Fuchs Heterochromic Iridocyclitis
Unfortunately, research has not identified the exact etiology of FHI; there are, however, several factors which have been linked to the onset of the condition.
Toxoplasmosis is a parasitic disease that humans can catch from the faeces of infected cats and contaminated meat. While the condition may be harmless for some, it can cause significant problems for others and is associated with the onset of FHI.
Research has suggested that sympathetic dysfunction may be linked to the development of FHI due to the fact that sympathetic lesions can often be accompanied by iris hypochromia. From this, researchers have since introduced the notion that some ‘tropic’ defect within the sympathetic nervous system has inhibited the normal process of uveal pigmentation.
Herpes Simplex Virus
One case study showed an association between exposure to the herpes simplex virus (HSV) and Fuchs heterochromic iridocyclitis.
Diagnosis of Fuchs Heterochromic Iridocyclitis
Although some individuals may be aware of their iris heterochromia (having two different colored irides), they can be asymptomatic for several years prior to presentation. Unlike other cases of uveitides, they will often not experience pain, photophobia or redness. Typical complaints are floaters or secondary to cataract. There is no set diagnostic test for FHI. Therefore diagnosis is based on the constellation of clinical findings. Some of the following may be identified during physical examination by a medical professional.
Iris atrophy can precede heterochromia and is characterized by the iris having a moth-eaten appearance.
Iris heterochromia is seen in approximately 75-90% of those with FHI. The lighter of the two eyes is usually the affected eye. However, in some patients with lightly colored irides may have inverse heterochromia characterized by the loss of pale anterior stroma. This, in turn, leads to the exposure of darker iris pigment. Therefore, the affected eye’s iris will appear darker in color.
Iridocyclitis is a low-grade inflammatory reaction that is not responsive to the use of steroids. The flare and cells observed in FHI are thought to occur due to the breakdown of the blood-aqueous barrier which leads to the leakage of cells. Even though there is persistent inflammation, posterior synechiae is absent.
Keratic precipitates are stellate and fine in feature, and interconnected by fibrin bridges. In cases of FHI, they tend to involve the whole endothelial surface.
Iris Crystals and Nodules
Russell bodies are small, refractile iris crystals that can be observed on the surface of the iris in cases of FHI. Iris nodules can also be present in those with FHI, and their presence may initially lead to a misdiagnosis of granulomatous uveitis.
In most cases, the disease is not associated with systemic diseases and affects both women and men equally. Those who developed FHI tend to be aged between 29 and 44 years old and are often given a positive prognosis.
In cases of inflammation, therapy may not be required. As the majority of the cell and flare observed are caused by the breakdown of the aqueous blood barrier and not inflammation, corticosteroids are often ineffective in addressing the low-grade anterior chamber reaction seen in FHI.
Some patients may benefit from improved equivocal visual results following cataract extraction. Whereas those with vitreous floaters caused by inflammatory debris may be able to improve their vision by using para plana vitrectomy.