Currently there are no accepted diagnostic criteria or laboratory studies for FHI. Diagnosis is made through clinical history and physical examination. The classic triad of iridocyclitis, heterochromia, and cataract does not take into account the myriad of other findings that can be observed. Also, the differential diagnosis of iris heterochromia includes a variety of diseases from malignant melanoma to congenital Horner’s syndrome (see Table 22.1). As mentioned previously, heterochromia can often be subtle, particularly in dark irides. Therefore, it is more useful to look for subtle changes on the iris surface. The absence of heterochromia and the presence of vitreous opacities can often lead to misdiagnosis. Studies have found that in more than 70 % of cases of misdiagnosed FHI, posterior uveitis was the initial diagnosis [23]. Vitreous involvement often leads the clinician away from a diagnosis of FHI. Cataract development typically occurs later in FHI, which limits its use diagnostically.

Low-grade iridocyclitis, diffuse small KP and vitreous opacities with a lack of posterior synechie or cystoid macular edema may be more useful diagnostic criteria than the classic triad. As FHI typically has a fairly benign course, making the correct diagnosis early can save a patient from unnecessary treatments.

Cataract formation is the primary cause of vision loss in patients with FHI. Incidence of cataracts range from 15 to 80 % in FHI and are often correlated to chronicity of disease. Cataracts are typically posterior subcapsular, as seen with other types of uveitis due to chronic inflammation and topical steroid use. Surgery itself is no more technically difficult than other routine cataract surgery, and postoperative complications are less frequent than with other types of uveitis. Surgical complications include hyphema, vitreous hemorrhage, vitreous opacification, and cystoid macular edema. Rates of postoperative CSME are less than with other types of uveitis but more than with age-related cataracts [24]. Rarely, posterior synechiae can form after surgery. Pars plana vitrectomy can be considered to treat visual significant vitreous opacification following cataract extraction.

The incidence of secondary glaucoma is also significantly higher in FHI patients; reported prevalence ranges from 10 to 59 % [25]. The etiology of glaucoma is unknown but is thought to be multifactorial in origin. Degenerative changes of the trabecular meshwork are the most common cause of secondary glaucoma. IOP elevation is often isolated and intermittent early in the disease course developing over time into true glaucoma. Initially, the IOP elevation can be managed medically, but filtering surgery is often needed. Due to a high incidence of bleb failure in trabeculectomy, glaucoma drainage implant devices are usually the preferred surgical option [26].

FHI typically follows a benign course that does not warrant treatment. Common complications associated with uveitis, such as CME and posterior synechiae typically do not occur. Corticosteroids and other immunosuppressive medications have not been found to cure FHI or to improve visual outcomes. Short durations of topical corticosteroids can be helpful with IOP spikes or in the rare case of a patient who is experiencing symptoms due to increase in anterior chamber reaction. Long-term topical corticosteroid therapy can hasten cataract development and induce glaucoma in certain subsets of patients. Glaucoma is the most significant source of vision loss in these patients, and must be carefully managed. Most patients will fail medical treatment and require a glaucoma drainage implant. Cataracts can be safely removed in these patients with very good visual outcomes [27].