**Core Concept**
Retinoblastoma is a malignant tumor of the retina, and glaucoma in this context refers to secondary glaucoma, which is a complication of the tumor. The underlying cause is related to the obstruction of the aqueous humor outflow due to the tumor's growth.

**Why the Correct Answer is Right**
The correct answer is related to the pathophysiology of secondary glaucoma in retinoblastoma. The tumor can grow to obstruct the trabecular meshwork, the site where aqueous humor is drained from the eye. This obstruction leads to an increase in intraocular pressure (IOP) due to the accumulation of aqueous humor. As a result, the iris becomes bowed forward, and the angle between the iris and the cornea is closed, further reducing aqueous outflow. This mechanism is responsible for the development of glaucoma in retinoblastoma patients.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not relate to the pathophysiology of secondary glaucoma in retinoblastoma. While cataracts can cause glaucoma, they are not directly associated with retinoblastoma.
* **Option B:** This option is incorrect because it refers to a different type of glaucoma altogether. Neovascular glaucoma is associated with conditions such as diabetic retinopathy, not retinoblastoma.
* **Option C:** This option is incorrect because it is not directly related to the development of glaucoma in retinoblastoma. While retinal detachment can cause vision loss, it is not the primary cause of glaucoma in this context.

**Clinical Pearl / High-Yield Fact**
In retinoblastoma, the presence of glaucoma is a poor prognostic sign, indicating advanced disease. Early recognition and management of secondary glaucoma are crucial to preserve vision and prevent further complications.

**Correct Answer: C. Obstruction of the trabecular meshwork by the tumor.**