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The pupillary light reflex (PLR) or photopupillary reflex is a reflex that controls the diameter of the pupil, in response to the intensity of light that falls on the retinal ganglion cells of the retina in the back of the eye, thereby assisting in adaptation of vision to various levels of lightness/darkness.
The pupillary reflex results in the pupil constricting (left) and dilating (right) These include the pupillary light reflex and accommodation reflex . Although the pupillary response , in which the pupil dilates or constricts due to light is not usually called a "reflex", it is still usually considered a part of this topic.
The Marcus Gunn pupil is a relative afferent pupillary defect indicating a decreased pupillary response to light in the affected eye. [3] In the swinging flashlight test, a light is alternately shone into the left and right eyes. A normal response would be equal constriction of both pupils, regardless of which eye the light is directed at.
When the optic nerve is damaged, the sensory (afferent) stimulus sent to the midbrain is reduced. The pupil, responding less vigorously, dilates from its prior constricted state when the light is moved away from the unaffected eye and towards the affected eye. This response is a relative afferent pupillary defect (or Marcus Gunn pupil). [1]
In a person with normal ocular alignment the light reflex lies slightly nasal from the center of the cornea (approximately 11 prism diopters—or 0.5mm from the pupillary axis), as a result of the cornea acting as a temporally-turned convex mirror to the observer.
Similarly to the pupillary light reflex, the pupillary dark reflex is an autonomic reflex that controls pupil diameter to accommodate for decreases in illumination as perceived by the retina. Lower light intensity causes pupil dilation, and the decrease of light stimulation of one eye will cause pupillary dilation of both eyes.
ALEX: I’d lock eyes with a picture of Bryan for five minutes before I could walk away. There’s one picture in the upstairs hallway. It’s his senior picture from high school. He’s looking directly into the camera. When you walk by it, it looks like he’s following you with his eyes. I would go to walk by him, and I couldn’t walk away.
A consensual response is any reflex observed on one side of the body when the other side has been stimulated.. For example, if an individual's right eye is shielded from light, while light shines into the left eye, constriction of the right pupil will still occur (the consensual response), along with the left (the direct response).