**Core Concept**
The management of an 18-month-old child with bilateral medial deviation of the eyes involves a thorough assessment to determine the underlying cause, which could be a congenital or acquired condition. The first step is to identify the type of strabismus, which can be either congenital or acquired, and to evaluate for any systemic or neurological conditions that may be contributing to the deviation.

**Why the Correct Answer is Right**
The first step in managing a child with bilateral medial deviation of the eyes is to perform a thorough ophthalmological examination, including a detailed assessment of the ocular alignment and motility, to determine the type of strabismus. This involves evaluating the position of the eyes in different directions, including looking straight ahead, to the left, and to the right. The examiner should also check for any signs of amblyopia, which is a condition where the vision in one eye is reduced due to abnormal visual development.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not relevant to the management of strabismus in a child. The first step in managing strabismus is not to refer the child to a pediatrician or a general practitioner.

**Option B:** While a comprehensive medical history is important, it is not the first step in managing a child with bilateral medial deviation of the eyes. A thorough ophthalmological examination is necessary to determine the underlying cause of the strabismus.

**Option C:** A complete blood count (CBC) is not a relevant diagnostic test for strabismus in a child. The first step in managing strabismus is to perform a thorough ophthalmological examination.

**Option D:** A CT scan of the head is not a necessary diagnostic test for strabismus in a child. While a CT scan may be necessary in certain cases, such as when there is a suspicion of a neurological condition, it is not the first step in managing a child with bilateral medial deviation of the eyes.

**Clinical Pearl / High-Yield Fact**
In children with strabismus, it is essential to evaluate for amblyopia, which can lead to permanent vision loss if left untreated. The American Academy of Pediatrics recommends that children with strabismus be evaluated by an ophthalmologist within the first few months of life.

**Correct Answer:** A. Perform a thorough ophthalmological examination.