**Core Concept**
The white pupillary reflex, also known as the leukocoria, is a condition where the pupil appears white or has a white reflection. This phenomenon occurs due to the light being reflected from the retina or the vitreous humor in the eye, rather than being absorbed.

**Why the Correct Answer is Right**
Leukocoria is often associated with conditions that affect the retina or the optic nerve, such as retinoblastoma, cataracts, or retinal detachment. In retinoblastoma, a malignant tumor forms in the retina, causing the white reflex. The tumor scatters the light, giving it a white appearance. This condition is a medical emergency and requires prompt attention.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because leukocoria is not typically associated with conditions that affect the iris or the cornea, such as uveitis or keratitis.

**Option B:** This option is incorrect because leukocoria is not a common feature of glaucoma, which is a group of eye conditions that damage the optic nerve.

**Option C:** This option is incorrect because leukocoria is not typically associated with conditions that affect the eyelids or the orbit, such as blepharitis or orbital cellulitis.

**Clinical Pearl / High-Yield Fact**
In children, leukocoria is a classic sign of retinoblastoma, and any white pupillary reflex should be investigated immediately with an ophthalmologic examination.

**Correct Answer: D. Retinoblastoma.**