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Why We Have Pupils
The pupil controls how much light is let into the eye.It is very similar to a camera aperture which allows more light in for more exposure. At night, our pupils dilate to allow in more light to maximize our vision. In the bright sunlight, our pupil shrinks to a very small diameter to allow us to function normally. Otherwise, we would be very light-sensitive, and this could affect photoreceptors in our retina.
Also, when we look at something at a very close distance such as when reading a book, our eyes converge and our pupils shrink. When our pupils shrink, it is similar to looking through a pinhole. Looking through a small hole reduces peripheral blur and increases the depth of focus. This improves overallvisual acuity.Normal pupil size is between 2 and 8mm.
What Controls the Pupil?
Our parasympathetic system controls everyday activities such as rest, slowing the heart rate, and things like digestion. It controls the pupil size during normal activities during the day and acts to change the pupil size depending on how much light is present. The sympathetic system is a protective system and gives us the typical “fight or flight” responses. If we are scared or feel fear, our pupils dilate very large. This is thought to allow light in so our responses are quicker.
Significance in Healthcare
Examination of the pupil is important because it can denote problems in the pathways controlling the pupil. A light is used to check the pupils, first to check the size and symmetry on each side, and then the light is swung from side to side; A “relative affarent pupillary defect” occurs when the intensity of light entering the eye is not transmitted along the light reflex pathway, and instead of the pupil becoming smaller with the bright shiny light, it becomes bigger. It is a paradoxical movement suggesting that there is a problem along the visual pathway of the affected eye.
Frequently Asked Questions
Thelensis a transparent eye structure that helps us focus on things at varying distances. It is located behind the pupil and iris. The natural lens that we are born with is called the crystalline lens.
8 SourcesVerywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.Mathôt S.Pupillometry: psychology, physiology, and function.J Cogn. 2018;1(1):16. doi:10.5334/joc.18Chen Y, Perusek L, Maeda A.Autophagy in light-induced retinal damage.Exp Eye Res. 2016;144:64-72. doi:10.1016/j.exer.2015.08.021Mathôt S, Ivanov Y.The effect of pupil size and peripheral brightness on detection and discrimination performance.PeerJ. 2019;7:e8220. Published 2019 Dec 19. doi:10.7717/peerj.8220Mathôt S, Fabius J, Van Heusden E, Van der Stigchel S.Safe and sensible preprocessing and baseline correction of pupil-size data.Behav Res Methods. 2018;50(1):94-106. doi:10.3758/s13428-017-1007-2Broadway DC.How to test for a relative afferent pupillary defect (RAPD).Community Eye Health J. 2016;29(96):68069.Wulf MJ, Tom VJ.Consequences of spinal cord injury on the sympathetic nervous system.Front Cell Neurosci. 2023;17:999253. doi:10.3389/fncel.2023.999253Cleveland Clinic.Dilated pupils (mydriasis).Steck RP, Kong M, McCray KL, Quan V, Davey PG.Physiologic anisocoria under various lighting conditions.Clin Ophthalmol. 2018;12:85-89. doi:10.2147/OPTH.S147019
8 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.Mathôt S.Pupillometry: psychology, physiology, and function.J Cogn. 2018;1(1):16. doi:10.5334/joc.18Chen Y, Perusek L, Maeda A.Autophagy in light-induced retinal damage.Exp Eye Res. 2016;144:64-72. doi:10.1016/j.exer.2015.08.021Mathôt S, Ivanov Y.The effect of pupil size and peripheral brightness on detection and discrimination performance.PeerJ. 2019;7:e8220. Published 2019 Dec 19. doi:10.7717/peerj.8220Mathôt S, Fabius J, Van Heusden E, Van der Stigchel S.Safe and sensible preprocessing and baseline correction of pupil-size data.Behav Res Methods. 2018;50(1):94-106. doi:10.3758/s13428-017-1007-2Broadway DC.How to test for a relative afferent pupillary defect (RAPD).Community Eye Health J. 2016;29(96):68069.Wulf MJ, Tom VJ.Consequences of spinal cord injury on the sympathetic nervous system.Front Cell Neurosci. 2023;17:999253. doi:10.3389/fncel.2023.999253Cleveland Clinic.Dilated pupils (mydriasis).Steck RP, Kong M, McCray KL, Quan V, Davey PG.Physiologic anisocoria under various lighting conditions.Clin Ophthalmol. 2018;12:85-89. doi:10.2147/OPTH.S147019
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
Mathôt S.Pupillometry: psychology, physiology, and function.J Cogn. 2018;1(1):16. doi:10.5334/joc.18Chen Y, Perusek L, Maeda A.Autophagy in light-induced retinal damage.Exp Eye Res. 2016;144:64-72. doi:10.1016/j.exer.2015.08.021Mathôt S, Ivanov Y.The effect of pupil size and peripheral brightness on detection and discrimination performance.PeerJ. 2019;7:e8220. Published 2019 Dec 19. doi:10.7717/peerj.8220Mathôt S, Fabius J, Van Heusden E, Van der Stigchel S.Safe and sensible preprocessing and baseline correction of pupil-size data.Behav Res Methods. 2018;50(1):94-106. doi:10.3758/s13428-017-1007-2Broadway DC.How to test for a relative afferent pupillary defect (RAPD).Community Eye Health J. 2016;29(96):68069.Wulf MJ, Tom VJ.Consequences of spinal cord injury on the sympathetic nervous system.Front Cell Neurosci. 2023;17:999253. doi:10.3389/fncel.2023.999253Cleveland Clinic.Dilated pupils (mydriasis).Steck RP, Kong M, McCray KL, Quan V, Davey PG.Physiologic anisocoria under various lighting conditions.Clin Ophthalmol. 2018;12:85-89. doi:10.2147/OPTH.S147019
Mathôt S.Pupillometry: psychology, physiology, and function.J Cogn. 2018;1(1):16. doi:10.5334/joc.18
Chen Y, Perusek L, Maeda A.Autophagy in light-induced retinal damage.Exp Eye Res. 2016;144:64-72. doi:10.1016/j.exer.2015.08.021
Mathôt S, Ivanov Y.The effect of pupil size and peripheral brightness on detection and discrimination performance.PeerJ. 2019;7:e8220. Published 2019 Dec 19. doi:10.7717/peerj.8220
Mathôt S, Fabius J, Van Heusden E, Van der Stigchel S.Safe and sensible preprocessing and baseline correction of pupil-size data.Behav Res Methods. 2018;50(1):94-106. doi:10.3758/s13428-017-1007-2
Broadway DC.How to test for a relative afferent pupillary defect (RAPD).Community Eye Health J. 2016;29(96):68069.
Wulf MJ, Tom VJ.Consequences of spinal cord injury on the sympathetic nervous system.Front Cell Neurosci. 2023;17:999253. doi:10.3389/fncel.2023.999253
Cleveland Clinic.Dilated pupils (mydriasis).
Steck RP, Kong M, McCray KL, Quan V, Davey PG.Physiologic anisocoria under various lighting conditions.Clin Ophthalmol. 2018;12:85-89. doi:10.2147/OPTH.S147019
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