**Core Concept**
Congenital Glaucoma is a rare condition affecting infants and young children, characterized by increased intraocular pressure (IOP) due to developmental anomalies in the trabecular meshwork or angle structures of the eye. This results in corneal edema, photophobia, and vision loss.

**Why the Correct Answer is Right**
The earliest symptom of Congenital Glaucoma is photophobia, which is caused by the corneal edema and increased IOP. When light enters the eye, it stimulates the corneal nerves, leading to pain and discomfort. This symptom is often accompanied by tearing, blepharospasm, and squinting. The corneal edema can be detected by examining the cornea for signs of thinning, hazing, or vascularization.

**Why Each Wrong Option is Incorrect**
* **Option A:** Buphthalmos (enlarged eyeball) is a characteristic sign of Congenital Glaucoma, but it is not the earliest symptom.
* **Option B:** Vision loss is a consequence of prolonged increased IOP, but it is not the initial presenting symptom.
* **Option D:** Eye pain is a symptom of Congenital Glaucoma, but it is not the earliest symptom, as it is often associated with photophobia and corneal edema.

**Clinical Pearl / High-Yield Fact**
In Congenital Glaucoma, the corneal thickness can be measured to assess the severity of the condition. A decrease in corneal thickness can be an early indicator of glaucoma in infants.

**Correct Answer:** C.