TOPIC:

When differentiating ocular toxoplasmosis (OT) from ocular toxocariasis (OTC), the clinical features can be organized as follows:

1. Lesion Location and Appearance:

Ocular Toxoplasmosis typically manifests as focal retinochoroiditis with well-defined borders, usually involving the posterior pole and occasionally extending to the optic nerve (forming traction bands, known as Franceschetti’s sign). These lesions display central necrosis surrounded by peripheral pigmentation and often affect the macula, leading to vision impairment. Recurrences are common, resulting in multiple retinal scars over time.

Ocular Toxocariasis usually presents with large peripheral granulomas, which can be subretinal, retinal, or vitreous in location. The granulomas, especially in the posterior pole, may cause marked vitreous inflammation and retinal traction. Fibrotic bands associated with these lesions often result in tractional retinal detachment, as the granulomas and surrounding inflammation cause significant retinal distortion.


2. Vitreous Involvement:

In ocular toxoplasmosis, vitreous inflammation is present but typically milder, with mild to moderate vitritis, especially near active lesions.

In ocular toxocariasis, severe vitritis is more prominent, often obscuring fundus details. The vitreous inflammation may be marked, with snowbank-like opacities in advanced cases.


3. Systemic Association and History:

Ocular toxoplasmosis may occur in patients with a history of systemic toxoplasmosis, especially in those who are immunocompromised. There are no systemic allergic responses.

Ocular toxocariasis is frequently associated with eosinophilia and elevated IgE levels due to infection by Toxocara larvae (from pets or contaminated soil). It commonly affects children but can present in adults, especially in late-stage disease.


4. Retinal Detachment:

In ocular toxoplasmosis, complicated cases may lead to tractional retinal detachment, though it is less common than in OTC.

Ocular toxocariasis often results in tractional retinal detachment due to the fibrotic bands pulling on the retina, especially in long-standing cases.


5. Inflammatory Response:

In ocular toxoplasmosis, inflammation is localized around the retinal scar and may lead to peripheral neovascularization and scarring from chronic inflammation.

Ocular toxocariasis has a more diffuse granulomatous inflammation, often extending to the surrounding vitreous, leading to more significant vitreoretinal traction.


6. Imaging Findings (OCT/B-Scan):

Ocular toxoplasmosis on OCT shows retinal thinning and necrosis with adjacent retinal elevation due to inflammation.

Ocular toxocariasis on OCT reveals retinal granulomas and overlying vitreous bands causing retinal traction. B-scan ultrasound can show denser vitreous opacities and retinal detachment.


Differentiating Retinal Traction Bands in OT and OTC:

In ocular toxoplasmosis (Franceschetti’s sign), traction bands are thin and delicate, typically extending from an old retinochoroiditis scar to the optic disc. These scars have well-defined borders with central atrophy and peripheral hyperpigmentation.

In ocular toxocariasis, the fibrous bands are thicker and more irregular, associated with granulomatous inflammation rather than a chorioretinal scar. These bands often cause significant vitreoretinal traction, leading to more frequent retinal detachment or folds.


Summary:

Ocular toxoplasmosis involves the posterior pole, less severe vitreous inflammation, and characteristic retinochoroiditis scars, while ocular toxocariasis features peripheral granulomas, severe vitritis, and more pronounced retinal traction from fibrous bands. Imaging (OCT and B-scan) plays a crucial role in differentiating the two conditions.


This structured approach highlights the essential differences in clinical and imaging features between OT and OTC.