**Question:** A HIV patient complains of visual disturbances. Fundal examination shows bilateral retinal exudates and perivascular haemorrhages. Which of the following viruses are most likely to be responsible for this retinitis -

A. Herpes Simplex Virus (HSV)
B. Cytomegalovirus (CMV)
C. Varicella-Zoster Virus (VZV)
D. Toxoplasma gondii

**Correct Answer: .**

**Core Concept:** Retinitis is an inflammation of the retina, which can be caused by various infectious agents. In the context of HIV-positive patients, the most likely culprits among the provided options are Herpes Simplex Virus (HSV), Cytomegalovirus (CMV), and Toxoplasma gondii.

**Why the Correct Answer is Right:** The correct answer is a combination of clinical presentation, epidemiologic considerations, and pathophysiology.

1. **Herpes Simplex Virus (HSV):** Although HSV can cause retinal infections, they are more commonly associated with keratitis (inflammation of the cornea) and herpetic uveitis (inflammation of the uvea). In addition, HSV typically presents with acute onset, while the described retinitis has a chronic course.
2. **Cytomegalovirus (CMV):** CMV can cause retinitis, particularly in immunocompromised patients, like HIV-positive individuals. However, both HSV and CMV typically present as acute episodes, whereas the described retinitis is chronic.
3. **Toxoplasma gondii:** This protozoan parasite can cause ocular toxoplasmosis, which is also a cause of chronic retinitis. However, Toxoplasma gondii is more commonly associated with uveitis and retinochoroiditis (inflammation of the retina and choroid), not retinal exudates and perivascular haemorrhages.

**Why Each Wrong Option is Incorrect:**

1. **Herpes Simplex Virus (HSV):** While HSV can cause retinal infections, it typically presents as acute episodes, making it less likely in this chronic case.
2. **Cytomegalovirus (CMV):** Similar to HSV, CMV also presents as acute episodes, making it less likely in this chronic case.
3. **Toxoplasma gondii:** This protozoan parasite is more commonly associated with uveitis and retinochoroiditis, not retinal exudates and perivascular haemorrhages.

**Clinical Pearl:** In HIV-positive patients, other differential diagnoses for retinal involvement include toxoplasmosis, syphilis, and histoplasmosis. These conditions should be considered in the differential diagnosis to confirm the correct diagnosis.

**Core Concept:** HIV weakens the immune system, making the patient more susceptible to opportunistic infections caused by pathogens like Toxoplasma gondii, which can lead to chronic retinitis.

**Why Each Wrong Option is Incorrect:**

1. Herpes Simplex