**Core Concept**
Ophthalmia neonatorum, also known as neonatal conjunctivitis, is an infection of the conjunctiva and cornea in newborns. It can be caused by various pathogens, including bacteria, viruses, and chlamydia.

**Why the Correct Answer is Right**
The most common causes of ophthalmia neonatorum are bacterial, including Neisseria gonorrhoeae and Chlamydia trachomatis. Chlamydia trachomatis is the most common cause of ophthalmia neonatorum, accounting for approximately 20-50% of cases. The infection is usually acquired during passage through an infected birth canal.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because gonococcal ophthalmia neonatorum is a well-documented cause of the condition. Neisseria gonorrhoeae is a Gram-negative diplococcus that can cause severe conjunctivitis in newborns.
**Option B:** This option is incorrect because herpes simplex virus (HSV) can cause ophthalmia neonatorum, leading to severe conjunctivitis and potentially life-threatening keratitis. HSV is a common cause of neonatal conjunctivitis.
**Option C:** This option is incorrect because pneumocystis jirovecii (formerly known as Pneumocystis carinii) is not a common cause of ophthalmia neonatorum. While pneumocystis pneumonia (PCP) is a significant concern in immunocompromised patients, it is not typically associated with conjunctivitis in newborns.

**Clinical Pearl / High-Yield Fact**
A key aspect of diagnosing ophthalmia neonatorum is performing a thorough maternal history, including questions about sexually transmitted infections. This can help identify high-risk patients who may benefit from prophylactic antibiotic treatment.

**Correct Answer: D. Pneumocystis jirovecii**