Fig. 9.37 Chest X-ray showing calcified lesions due to histoplasmosis infection. (Reprinted with permission from Arévalo JF, Fernández CF, Mendoza AJ. Chapter 41: Fungal Infections. In: Retinal Imaging. Huang D, Kaiser PK, Lowder CY, Traboulsi EI, eds. Philadelphia: Mosby Elsevier: 2006; 366–774)

intravitreal injection of antifungal drugs may be indicated in cases with dense vitreous exudates or fulminant retinitis [51].

Blastomyces Dermatitidis

Chorioretinitis

Blastomyces dermatitidis is a thermally dimorphic fungus that grows in mycelial form. The geographic distribution of reported blastomycosis cases is fairly widespread in the United States. The disease has also been reported in Canada, Africa, the Middle East, India, and Poland. Although the incidence of ocular involvement is low, blastomycosis has been reported to involve essentially all the intraocular and periocular tissues [52].

Risk Factors

•Persons in areas with endemic disease with exposures to wooded sites (e.g., farmers, forestry workers, hunters, and campers)

•Immunocompromised individuals, such as those on chronic steroid therapy, organ transplant recipients, and patients with human immunodeficiency virus (HIV)

Pathogenesis

Except for rare cases of cutaneous inoculation caused by laboratory accidents or infected animal bites [53], the most common route of infection of blastomycosis is by inhalation of airborne spores that arise from the soil. Inside the body or when incubated at 37°C, the organism converts to the yeast form, which reproduces by budding. The pulmonary lesion may resolve, leaving no signs of previous infection. Hematogenous dissemination can produce cutaneous blastomycosis, blastomycosis of the bone marrow, blastomycosis of the male genitourinary system, or ophthalmic blastomycosis. Blastomyces dermatitidis causes a combination of acute suppurative and granulomatous inflammation.

Clinical Features

Ocular symptoms of blastomycosis include pain, redness, photophobia, and blurred vision. The ophthalmic manifestations include eyelid infection, conjunctivitis, keratitis, iritis, choroiditis, endophthalmitis, panophthalmitis, and orbital cellulitis.

Choroidal involvement in blastomycosis is unusual and can be seen clinically as one or more yellowish-white choroidal lesions (Fig. 9.38) and perivascular infiltrates [13].

Diagnosis

Hematoxylin–eosin, Gomori methenamine silver, periodic acid Schiff, and auramine are the stains used for B. dermatitidis identification. The organism grows well on Sabouraud agar, producing white to tan colonies. Blastomyces dermatitidis is dimorphic (septate mycelia and conidia). The organism grows almost exclusively in the yeast form, with hyphae only rarely found (Fig. 9.39).

Because of variations in both the systemic and the ocular manifestations of blastomycosis, diagnosis is based on a high index of suspicion. B. dermatitidis