SUPERStudy: Ocular Toxoplasmosis

By usmlevideoss

Introduction

Ocular toxoplasmosis is the most common cause of infectious chorioretinitis worldwide. It is caused by Toxoplasma gondii, a parasitic protozoan, and can occur due to congenital infection or reactivation of a latent infection. It is a major cause of vision loss if left untreated.

Etiology

  • Caused by Toxoplasma gondii infection.
  • Congenital transmission: Occurs when a mother contracts primary Toxoplasma infection during pregnancy.
  • Acquired infection: Results from ingestion of undercooked meat, exposure to contaminated water, or contact with cat feces containing oocysts.
  • Reactivation is common in immunocompromised individuals (e.g., HIV/AIDS).

Epidemiology

  • Common in developing countries, particularly in areas with high exposure to contaminated food or water.
  • In the U.S., it is an important cause of chorioretinitis and vision impairment.
  • Congenital toxoplasmosis is a significant cause of childhood blindness.
  • Risk is higher in immunocompromised individuals due to reactivation.

Pathophysiology

  • Toxoplasma gondii infects retinal cells, leading to inflammation and necrosis of the retina and adjacent choroid (chorioretinitis).
  • The immune response leads to scarring of the retina, contributing to visual impairment.
  • Reactivation occurs due to the rupture of tissue cysts, especially in immunocompromised individuals.
  • In congenital cases, retinal damage begins in utero and progresses postnatally.

Clinical Manifestations

  1. Ocular symptoms:
    • Blurred vision
    • Floaters
    • Photophobia
    • Eye pain (less common)
  2. Signs on fundoscopic examination:
    • Yellow-white, fluffy retinal lesions surrounded by retinal edema
    • “Headlight in the fog” appearance due to the lesion surrounded by vitritis
    • Old chorioretinal scars from previous infections
  3. Systemic manifestations (in congenital cases):
    • Hydrocephalus
    • Intracranial calcifications
    • Seizures

Diagnosis

  1. Clinical diagnosis (fundoscopy):
    • Characteristic yellow-white retinal lesions with vitritis
  2. Serologic tests:
    • Positive Toxoplasma-specific IgG (suggests past or chronic infection)
    • IgM positivity suggests acute or recent infection
  3. PCR testing:
    • Detects Toxoplasma DNA in aqueous or vitreous humor
  4. Imaging (in congenital cases):
    • Cranial CT or MRI to detect intracranial calcifications or hydrocephalus

Treatment

  1. Indications for treatment:
    • Active chorioretinitis near the macula or optic disc
    • Severe vision-threatening lesions
    • Immunocompromised patients
  2. Drug therapy:
    • Pyrimethamine + sulfadiazine (first-line therapy)
    • Leucovorin (folinic acid): Given to prevent bone marrow suppression
    • Trimethoprim-sulfamethoxazole can be used as an alternative
    • Corticosteroids: Used in cases of severe inflammation but only after starting antiparasitic therapy
  3. For immunocompromised patients:
    • Long-term suppressive therapy with trimethoprim-sulfamethoxazole to prevent reactivation

Prognosis

  • Good prognosis if treated early, especially in immunocompetent individuals.
  • Risk of recurrent infections or chorioretinal scarring leading to permanent vision loss.
  • In immunocompromised patients, outcomes depend on early detection and long-term therapy.

Memory Aid or Mnemonic:

TOXEYE:

  • T – Toxoplasma gondii (the causative agent)
  • O – Ocular lesion (often near the macula)
  • X – X-ray like appearance (the classic lesion looks like a “headlight in the fog”)
  • E – Exposure (to cats or undercooked meat)
  • Y – Yield to antibiotics (TMP-SMX treatment)

 

TOXEYE helps recall the etiology, characteristic presentation, risk factors, and treatment for ocular toxoplasmosis. Remember the connection to cats and the importance of targeted antibiotic therapy.

SUPERPoint: Ocular toxoplasmosis is the leading cause of infectious chorioretinitis and presents with blurred vision, floaters, and retinal lesions. It requires antiparasitic therapy (pyrimethamine + sulfadiazine) and long-term monitoring to prevent recurrence and vision loss.

SUPERFormula: HIV/AIDS patient presents with a history of floaters and blurred vision + congenital infection or reactivation + fluffy yellow-white retinal lesion + “Headlight in the fog” appearance  +  vitritis + blurred vision + antiparasitic treatment = Ocular Toxoplasmosis