OcuLearning › Systemic
Ocular Histoplasmosis
ROUTINE — Systemic
Symptoms
- often asymptomatic (discovered on routine exam)
- metamorphopsia or central scotoma (if cnv develops)
- decreased or distorted central vision
- history: geographic exposure to ohio-mississippi river valley
Clinical Findings
Hallmark triad
- histo spots: multiple small (<1 mm), yellow-white, punched-out chorioretinal scars
- peripapillary atrophy (ppa): ring of chorioretinal scarring around the optic disc
- absence of vitreous cells: quiet anterior chamber and vitreous (obligatory for diagnosis)
Mechanisms of vision loss
- choroidal neovascularization (cnv): gray-green subretinal patch with srf, lipid, or hemorrhage
- peripapillary region: most common site of cnv origin
- disciform scar: end-stage result of untreated macular cnv
Imaging
- oct: subretinal hyperreflective material with overlying srf
- ivfa: lacy early hyperfluorescence with late leakage confirming cnv
- oct-a: non-invasive detection of fibrovascular membranes
Etiology
Pathophysiology
- prior systemic infection with histoplasma capsulatum (fungal inhalation)
- hematogenous seeding of the choroid leaves residual "punched-out" scars
Disease nature
- pohs is a late sequela of healed infection, not an active ocular infection
- vision loss is driven by neovascularization, not primary inflammation
Red Flags
- macular cnv: urgent need for anti-vegf to prevent permanent disciform scarring
- vitritis/cells: presence of inflammation should prompt reconsideration of diagnosis (e.g., multifocal choroiditis)
- fellow-eye risk: ~20% lifetime risk of cnv in the second eye
Investigations
Clinical exam
- slit-lamp: essential to confirm absence of ac/vitreous cells
- dilated fundus exam: screen for active cnv (blood, fluid, or gray membranes)
Imaging & monitoring
- oct: primary tool for diagnosing and tracking cnv response
- ivfa: confirms leakage if oct is equivocal
- amsler grid: daily home self-monitoring for high-risk eyes
Treatment
Active CNV
- intravitreal anti-vegf: first-line therapy; excellent visual outcomes if prompt
- photodynamic therapy (pdt) or focal laser: rarely used/historical options
Inactive disease
- no treatment indicated for histo spots or ppa in the absence of cnv
Note on antifungals
- systemic or topical antifungals are NOT indicated; pohs is not an active infection
Clinical Pearl
histo spots, peripapillary atrophy, and a macular cnv make pohs — there is no active inflammation, so steroids are wrong and anti-vegf is right.
Differential Diagnosis
- • multifocal choroiditis with panuveitis (mcp): distinguished by presence of vitritis
- • old toxoplasmosis: typically larger, more pigmented/atrophic scars
- • angioid streaks: jagged lines radiating from the disc (different etiology)
- • birdshot chorioretinopathy: different spot morphology and location