**Core Concept**
The question pertains to the opportunistic infections associated with advanced HIV infection, specifically the pathogen responsible for causing blindness. In the context of HIV/AIDS, opportunistic infections often arise due to compromised immune function, allowing normally harmless pathogens to cause severe disease.

**Why the Correct Answer is Right**
Cytomegalovirus (CMV) is a common cause of blindness in advanced HIV infections. CMV retinitis is characterized by retinal necrosis and hemorrhage, leading to vision loss. The pathogenesis of CMV retinitis involves the reactivation of latent CMV in the retina, which is facilitated by the immunosuppressed state of the patient. The virus replicates within retinal cells, causing cellular damage and inflammation.

**Why Each Wrong Option is Incorrect**
* **Option A:** Toxoplasmosis is a common opportunistic infection in HIV/AIDS, causing encephalitis and focal neurological deficits, but it is not typically associated with blindness.
* **Option B:** Cryptococcal meningitis is another opportunistic infection in HIV/AIDS, characterized by cryptococcal capsular polysaccharide-induced inflammation in the central nervous system, but it is not associated with blindness.
* **Option D:** Pneumocystis jirovecii pneumonia (PCP) is a common opportunistic infection in HIV/AIDS, causing respiratory failure, but it is not associated with blindness.

**Clinical Pearl / High-Yield Fact**
CMV retinitis is often the first sign of advanced HIV infection, and its diagnosis is critical for initiating antiretroviral therapy and preventing further vision loss. A high index of suspicion for CMV retinitis is essential in patients with advanced HIV infection presenting with visual symptoms.

**Correct Answer:** C. Cytomegalovirus (CMV)