Normal Pupillary Response

The pupil is a small hole located in the center of the eye's iris that allows light to enter and pass through the lens of the eye. The size of the pupil is normally three to six millimeters in diameter, but this size increases and decreases in different situations. Normal pupillary responses involve reactivity to light, accommodation, stress, exertion and perceptions.

Light

• According to NursingCenter.com, the normal pupillary response to light is quick constriction. This response is tested by shining a low-beam light into the eye. Beginning at the outward corner of the eye, the light should slowly be passed across the eye, toward the inside corner. Each eye should be tested separately and the pupils should constrict rapidly when the light passes over them. Pupils that do not respond or that constrict slowly may be an indication of brain damage or increased intracranial pressure.

Accommodation

• Pupils will also constrict when they focus on an object that is close to the eyes in a reaction called accommodation. To test the papillary response to accommodation, begin by holding an object, such as a pen or your finger, approximately four inches from the person's nose. Ask them to look at the object, then look into the distance and then back to the object. The pupils should constrict when focusing on the close object and dilate when looking into the distance.

Stress

• Pupils also respond quickly to stressful situations. According to the University of Washington, the pupils dilate with stimulation of the sympathetic nervous system and constrict with stimulation of the parasympathetic nervous system. The sympathetic nervous system is stimulated when you are confronted with a stressful or threatening situation. This is commonly referred to as the "fight or flight" response. On the other hand, the parasympathetic nervous system is stimulated during a period of relaxation, which is commonly referred to as the "rest and digest" response.

Exertion

• According to the University of Pittsburgh School of Medicine, the pupils also respond to the level of exertion placed on the body. According to the website, "pupil diameter enlarges with increasing effort during performance." Interestingly, this response is the same for physical and mental exertion. Whether a person is lifting weights or remembering a set of numbers, the pupils will dilate. However, when the maximum effort is reached, the pupils will not dilate any further. In fact, they may even decrease in size.

Perceptions

• The University of Pittsburgh School of Medicine also explains that pupils will respond to positive and negative perceptions. In most cases, pupils will dilate significantly when viewing an interesting or pleasant picture. The pupils will only dilate a small amount when viewing an unpleasant picture. Neutral pictures yield an even smaller amount of pupil dilation.