What is the pupil of the eye

Written By The HealthMeth Team - Updated On Saturday, March 13, 2021 6:00 PM

pupil

The pupil, the human eye, the pupil, or the blackness of the eye is the black circle in the middle of the visible colored part of the eye known as the iris that is located in front of the lens of the eye, and through the pupil the light reaches the lens of the eye, [1] [2 ] and have the color black in the pupil normal lighting, due to light absorption by the entire retina and not reflected again, it is worth noting that the size of the pupil equal in both eyes in the normal position. [3]


Pupil function

To understand the function of the pupil, it should be noted that the process of vision takes place when the light from the image passes through the pupil and the lens of the eye to focus this image on the retina, which is the light-sensitive tissue in the back of the eye, and then the retina transforms this image into electrical signals that are transmitted through the nerve The visual to the brain, [4] and the importance of the pupil lies in controlling the amount of light that passes through it into the eye. In bright lighting, the diameter of the pupil decreases (i.e. shrinks) to reduce the amount of light entering the eye and thus help to see better, if this is not done. Too much light will enter the eye and negatively affect the photoreceptors on the retinaAnd, in contrast, at night the diameter of the pupil expands to allow more light to pass into the eye to improve vision as much as possible, in addition to that, the pupil improves vision when looking at something close to the distance, as it happens when reading a book, as the pupil contracts, which improves the sharpness Vision, reduces ambient blurring, and increases the depth of focus of vision. [5]


Pupil size

The size of the pupil ranges between 1.5-2 mm if the pupil shrinks, and 7.5-8 mm if it enlarges, and the size of the pupil varies from one person to another of the same age group, in addition to its size according to age, so its size is often larger in children and young adults compared to its size the elderly, [3] [6] the size of the pupil may change as a result of infection , too ? on the eye, and may also change as a result of certain diseases and disorders in the visual organs such as: occurrence of a malfunction in the paths that control the movement of the pupil, the blue waters known Balgluckoma Glaucoma, and its symptoms include enlarging the size of the pupil, and a cluster headache, which causes narrowing of the pupil, so the pupil of the eye must be carefully examined during an examination of the eyes and nerves to ensure that there are no problems in any of them. [7] [8]


The size of the pupil is controlled by two groups of smooth muscles in the iris, namely: the sphincter muscle and the dilated muscle, and the fact that the enlarged muscle appears radially in the iris, and when this muscle contracts, it causes the pupil to dilate and increase its size, and on the contrary, the sphincter appears in the form of a ring On the border of the pupil, and when this muscle contracts, the pupil shrinks and decreases in size. It should be noted that the two nervous systemSympathetic and parasympathetic control the size of the eye's pupil. In the normal position and during normal daily practices, the parasympathetic system is the system that controls the size of the pupil based on the amount of light in the surrounding, while the sympathetic system is the sympathetic system that controls the ball response. Fight or flight response is the control of the size of the pupil of the eye in the case of fear, as it increases the size of the pupil to allow more light to pass into the eye, so the body's reaction to the source of fear is faster. [5]


Examination of the pupils

During a routine eye examination, the doctor examines the pupil of the eye, monitors its functions, and makes sure that there are no problems in it. The examination is performed as follows: [3]

  • The examination is performed in a room with dim lighting.
  • A beam of light is directed for a short time at one eye several times while the person is looking far away, and the pupil response is observed in both eyes.
  • The light is alternately directed towards each eye and the pupil responds again to the light. This method is known as the Marcus Gunn pupil test, and it is also called the Swinging-flashlight test. It is worth noting that the pupil It interacts with light directly and indirectly, and the reaction of the pupil when confronted with direct lighting is called the direct response, and the reaction of the other pupil then is called the harmonic response.
  • The examiner raises the room lighting slightly and asks the patient to focus on a hand- moving object near the patient's nose . This test checks the appropriate response of the pupil.
  • The response of the pupils is monitored, so if the pupils are normal and respond to light normally, the doctor will record this abbreviation (PERRLA) in the patient's file, which is an abbreviation for the phrase “the pupils are equal, round, and interact with light appropriately.” The pupil is considered abnormal if it fails to contract upon exposure To light or fail to expand upon exposure to dim light.


Disorders of the pupil

There are many conditions that affect the size, shape, or function of the pupil, including the following:

  • Discrepancy in the size of the pupils: The size of the pupils in both eyes is the same in the normal position, as is the case for their response to light, and if there is a difference in the size of the pupils, this condition is called anisocoria, and this condition may be normal and may be an indication of the presence of Specific problem. [9] [1]
  • Dilated pupil: If the size of the pupil is much larger than normal without a change in the ambient light, then the person often has mydriasis, and most of the time the dilated pupil of the eye does not respond to light and is called the fixed dilated pupil, but in some cases Cases The dilated pupil continues to respond when lighting changes, such as shrinking when exposed to intense light, and it is worth noting that this condition may be due to taking some types of drugs, or eye exposure to injury or injury, or brain injury , or suffering from some brain diseases or other diseases Such as Adie's tonic pupil or Adie syndrome or Holmes-Adie syndrome, which is a rare neurological disorder that affects the pupil of the eye. [10] [11]
  • Pupil constriction: In some cases, the pupils of one or both eyes may remain shrinking even when exposed to dim lighting, and this condition is known as abnormal narrowing of the pupil, and this condition may be an indication that the eye is not working as required or that it has some defect, it is possible The presence of a swelling inside the eye that causes the pupil to contract and prevents it from expanding, and this swelling may occur as a result of injury and wounding of the eye, or because of Uveitis, which is the swelling of the iris and surrounding tissues. [12]
  • Marx Gunn's pupil: Injury to Marx Gunn's pupil causes the pupil to dilate when exposed to bright light, rather than contracting it, and this dilation results in a variation in the size of the patient's pupils. [13]
  • Argyll Robertson's pupil: The term Argyll Robertson pupil refers to a constricted, irregularly shaped pupil that does not respond to direct bright light, but narrows when adapted to ambient light. [14]
  • Coloboma: A person suffers a coloboma when a disorder occurs when a part of the eye parts forms in the embryonic stage, and if the iris is infected with a coloboma, the pupil appears longer than normal and may take a shape similar to a keyhole. [15]
  • The third cranial nerve palsy: causes paralysis of cranial nerve III expansion in a Albabaan, often occurs due to increased pressure on a nerve that controls eye movement, it is worth mentioning that the third cranial nerve palsy is one of the serious cases. [15]
  • Exposure to trauma: Trauma and strikes that affect the iris are among the common causes that may change the shape of the pupil, and the cause of the trauma may be some complications of eye surgeries such as: cataract surgery or lens implantation while keeping the lens Natural or refractive lens replacement, and it is worth noting that most injuries may change the shape of the pupil without affecting its response to light and its adaptation to ambient light. [3]


References

  1. ^ A b "Pupillary disorders Including Anisocori , Www.hopkinsmedicine.org , Retrieved 3-9-2020. Edited by .
  2. "Anatomy of the eye , www.moorfields.nhs.uk , Retrieved 3-9-2020. Edited.
  3. ^ A b t w , "Pupil: The Eye 's Of the Aperture , Www.allaboutvision.com , Retrieved 3-9-2020. Edited by .
  4. "Retina , www.medlineplus.gov , Retrieved 3-9-2020.
  5. ^ A b , "Why Reviews Our Eyes Have Pupils , Www.verywellhealth.com , Retrieved 3-9-2020. Edited by .
  6. , Pupil Size , www.link.springer.com/, Retrieved 3-9-2020. Edited.
  7. , "Pupil eye anatomy , www.britannica.com , Retrieved 3-9-2020.
  8. , "Pupil Size and Your Health , www.verywellhealth.com , Retrieved 3-9-2020."
  9. , "Pupils, Unequal , www.msdmanuals.com , Retrieved 3-9-2020.
  10. "Why Do the My Pupils of Big the Look? , The www.webmd.com , Retrieved 3-9-2020. Edited by .
  11. "Adie Syndrome , www.rarediseases.org , Retrieved 3-9-2020.
  12. , "What ' Is Eye 's Miosis? , The www.webmd.com , Retrieved 3-9-2020. Edited by .
  13. , "What ' Is of a Pupil , Marcus Gunn , ? , Www.medicalnewstoday.com The , Retrieved 3-9-2020. Edited by .
  14. , “Argyll Robertson pupil , www.radiopaedia.org , Retrieved 3-9-2020.
  15. ^ A b , "What ' Your Can Tell You Pupils About Your Health , the www.webmd.com , Retrieved 3-9-2020. Edited by .