Again, we think of the eye receiving signals and sending them to the brain, but we don’t always think of the brain sending messages back.įor all this to take place normally, one needs an intact afferent and efferent pathway to exist. A brain signal must be sent back to the tiny constricting muscles in the eye and cause them to contract. Humans are not consciously aware of this reflex but it happens rapidly. “this is to much light, I want to close the shade and reduce incoming light ASAP.” The brain must first receive this bright burst of light and send a signal back to eye (actually both eyes, they work as a unit in this case) and say The pupil immediately constricts to reduce the amount of incoming light. The basic manner in which an observer knows this is true is when he/she shines a bright penlight into a persons eye. But the brain also sends signals back to the eye in much smaller numbers ( efferent pathway). We generally look at the eye as a one-way street, light goes in and is processed by the eye and brain to create a picture of the world ( afferent pathway). Pupillary function is interesting but quite complicated. This blog is not meant to address acute neurosurgical emergencies. The “ blown pupil“, a fixed dilated pupil next to a normal-size reacting pupil is an ominous neurological sign and strongly suggests elevated intracranial pressure and a need for immediate intervention and scanning of the brain. The initial evaluation of the pupils is critical in the emergency room in evaluating any patients with head trauma. This self-adjusting structure is critical in understanding the optics of the eye, but I will focus on how the pupil is important in Traumatic Brain Injury (TBI). The surrounding tissue, the iris, is the colored portion of the eye (blue, green, and brown) which closes down when light is bright and opens up in the dark. What is the pupil? People know it as a black circle in the middle of the eye which responds to light. The eye is often described as the window to the soul.
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