**Question:** A mature uniocular cataract in a 3-year-old child:

A. Cataract due to trauma
B. Congenital cataract
C. Inherited cataract
D. Secondary cataract

**Core Concept:** Cataract is a condition characterized by the clouding of the lens within the eye, impairing vision. In a 3-year-old child, the most common type is congenital cataract, which can be further classified into primary and secondary cataracts. Primary congenital cataracts are due to genetic factors, while secondary cataracts can be caused by factors like trauma, infections, or medications.

**Why the Correct Answer is Right:**

B. Congenital cataract is the correct answer for a mature uniocular cataract in a 3-year-old child. Congenital cataracts develop before birth or shortly after birth and affect the child's vision. In this case, we are considering a primary congenital cataract, meaning it develops due to genetic factors.

**Why Each Wrong Option is Incorrect:**

A. Trauma-induced cataracts are usually acute and transient, leading to a different clinical presentation than the mature uniocular cataract described in the question.
C. Inherited cataracts are usually bilateral and can present at birth or develop later in childhood, not specifically a 3-year-old child with a mature uniocular cataract.
D. Secondary cataracts can be caused by factors like trauma, infections, or medications. However, in this case, the cataract is mature, suggesting it developed before birth or very early in life, making a secondary cause less likely.

**Clinical Pearl:**

In children, a mature uniocular cataract in a 3-year-old child should raise suspicion for congenital cataract due to genetic factors. Prompt diagnosis and management can prevent vision loss and ensure appropriate referral for further genetic counseling and management options.