Blind, but still with eyes to see.

The first time I read through this article it threw me for a loop: a patient at a hospital in Geneva, Switzerland referred to by the initials 'TN' suffered two strokes a couple of weeks apart. Each CVA damaged one half of his visual cortex, thus rendering him completely blind for all intents and purposes. While he was recovering, physicians discovered that TN still had the ability to read the facial expressions of people around him and correctly interpret their emotional states. Some tests showed that his amygdala was still operational, which lead neurologists to wonder what else he was capable of without being consciously aware of it. Just to see what would happen, a group of visiting researchers set up a simple obstacle course in a hallway and convinced TN to walk through it even though he required a cane to navigate under normal circumstances.

He was able to do it even though he is clinically blind.

As it turns out, TN's eyes are still fully operational even though his visual cortex is dead, for all intents and purposes. This means that information is still being transmitted to his brain by the optic nerves and the other parts of his brain involved in processing certain aspects of visual information are still functioning normally. Thus, while there is no conscious concept of what is around him the unconscious aspects of vision are still available to TN and are usable to a certain degree. Blindsight, defined as the ability to respond in the appropriate manner to visual input without the feeling of having perceived it is a rare condition but it is known and has been documented by the medical field.

Download the video recording from the article I linked to; give it a watch, it's wild.