This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Medicine
A two-month-old infant presents with irritability and lethargy. The parents state he was well until he rolled off the couch onto the floor on the previous day. On examination, he is inconsolable and afebrile. The fontanels are full and tense. He has a generalized tonic-clonic seizure in your office. The most impoant additional diagnostic study is: 
Select and explain. 
A. Serum calcium, phosphorus, and alkaline phosphatase levels, B. Viral cultures of nasopharyngeal swab, C. Retinoscopic Exam, D. Serum ammonia level
C: Retinoscopic Exam
Answer: C: Retinoscopic Exam 
Explanation: Though infection must be considered as an etiology, acute trauma is more likely in this scenario. This case represents the classic picture of the shaken baby syndrome, which produces intracranial trauma without obvious external findings. This infant is critically ill and lacks preceding illness or constitutional symptoms. The tense fontanelle reflect increased intracranial pressure. A retinoscopic exam most often would reveal retinal hemorrhages that would confirm the diagnosis. A history of trauma, which does not correlate with the child's injury should ale health care providers to the possibility of child abuse. Ref: Ropper A.H., Samuels M.A. (2009). Chapter 35. Craniocerebral Trauma. In A.H. Ropper, M.A. Samuels (Eds), Adams and Victor's Principles of Neurology, 9e.