**Core Concept**
Maturity-onset diabetes of the young (MODY) is a form of diabetes mellitus characterized by an autosomal dominant inheritance pattern and early onset, typically before the age of 25. Ophthalmoscopy is a crucial diagnostic tool in patients with MODY to detect and manage complications such as diabetic retinopathy.

**Why the Correct Answer is Right**
In MODY, the risk of developing diabetic retinopathy is significantly lower compared to type 1 and type 2 diabetes. However, given the younger age of onset and potential for longer disease duration, ophthalmoscopy should be performed at a younger age to detect and manage diabetic retinopathy early. The American Diabetes Association recommends that patients with MODY undergo annual dilated eye exams starting at the age of 10, regardless of the presence of symptoms.

**Why Each Wrong Option is Incorrect**
**Option A:** Performing ophthalmoscopy at an older age, such as 40 or 50, would miss the opportunity to detect diabetic retinopathy early in the disease course.
**Option B:** Delaying ophthalmoscopy until symptoms of diabetic retinopathy appear would result in delayed diagnosis and treatment, potentially leading to vision loss.
**Option C:** Not performing regular ophthalmoscopy in patients with MODY would leave them at risk for undetected and untreated diabetic retinopathy.

**Clinical Pearl / High-Yield Fact**
Patients with MODY should undergo annual dilated eye exams starting at the age of 10 to detect and manage diabetic retinopathy early, regardless of the presence of symptoms.

**Correct Answer: A. 10 years old**