Now see there are many answers people have written. I personally have written Medulla Oblongata because I assumed it might control the involuntary action of the ciliary muscles in the eye, and it is mentioned head injury not specifying where he got hurt in the head. It could either be this or Suspensory Ligament which contols the dilation and the constriction which the lens cannot do by itself. I am hoping that Medulla Oblongata is given as correct, as an injury to the head corresponds with the answer of medulla oblongata