Amanda, The ability to track is both cognitive as well as a function of the oculomotor system. It is very common after a traumatic injury to the brain to see problems with tracking objects. It is a very diffuse system controlled at higher cortical levels as well as brainstem levels. The control of pupil size and response to light is independent system. You can have unreactive pupils and normal vision.
Some brain injuries cause small pupils and some cause dilated pupils.
If the patient is able to respond than this situation is not a problem. Joeboo, Yes, this is a common situation. It is common for some TBI patients to have damage to there speech and comprehension centers. In right handed people this is usually of the left side of the brain. Damage to this center can cause the patient to lose the ability to name common objects correctly.