**Core Concept**
The question is testing the knowledge of investigations for chronic uveitis in a pediatric patient. Chronic uveitis can be caused by various underlying conditions, including autoimmune disorders, infections, and genetic mutations. In a 10-year-old boy, it is essential to consider systemic conditions that may be associated with uveitis.

**Why the Correct Answer is Right**
The correct investigation for chronic uveitis in a pediatric patient is HLA-B27 testing. This is because certain autoimmune conditions, such as ankylosing spondylitis, are associated with HLA-B27 positivity and can cause chronic uveitis. The HLA-B27 antigen is a genetic marker that is linked to these conditions. In children, the presence of HLA-B27 positivity can be a clue to underlying autoimmune disorders that may be causing the uveitis.

**Why Each Wrong Option is Incorrect**
**Option A:** Imaging studies such as MRI or CT scans may be useful in evaluating the extent of inflammation or detecting any complications, but they are not the primary investigation for chronic uveitis.
**Option B:** Blood cultures may be useful in cases of infectious uveitis, but they are not typically the first-line investigation for chronic uveitis.
**Option C:** Fluorescein angiography is a diagnostic tool used to evaluate the retinal vasculature, but it is not the primary investigation for chronic uveitis in a pediatric patient.

**Clinical Pearl / High-Yield Fact**
It is essential to remember that children with chronic uveitis should be evaluated for underlying systemic conditions, including autoimmune disorders and genetic mutations. A thorough history and physical examination, along with appropriate investigations, are crucial in making an accurate diagnosis and initiating appropriate treatment.

**Correct Answer:** C.