**Core Concept**
Persistent hyperplastic primary vitreous (PHPV) is a congenital anomaly characterized by the failure of the primary vitreous to regress, leading to a persistent, fibrotic, and vascularized structure within the eye. This condition often results in a range of ocular abnormalities, including microphthalmos, cataract, and retinal detachment.

**Why the Correct Answer is Right**
The correct answer is related to the differentiation of PHPV from retinoblastoma. Retinoblastoma is a malignant tumor of the retina, often presenting with leukocoria (white reflex) or strabismus. PHPV, on the other hand, typically presents unilaterally with leukocoria, strabismus, or nystagmus. The presence of exophthalmos or cataract is not a reliable feature to differentiate PHPV from retinoblastoma, as both conditions can present with these symptoms.

**Why Each Wrong Option is Incorrect**
* **Option A:** PHPV is generally unilateral, which is a true statement. This condition often affects one eye, and the affected eye may have a poor visual prognosis.
* **Option C:** PHPV may calcify, which is a true statement. Calcification within the fibrotic tissue of PHPV is a common finding.
* **Option D:** The statement that PHPV can be differentiated from retinoblastoma by the presence of exophthalmos or cataract is not entirely accurate. While these symptoms may be present in both conditions, they are not reliable distinguishing features.

**Clinical Pearl / High-Yield Fact**
PHPV is often associated with other congenital anomalies, such as microphthalmos, cataract, and retinal detachment. A high index of suspicion for PHPV should be maintained in cases of unilateral leukocoria or strabismus in children.

**Correct Answer:** D.