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What Is Pupil?

It is the center opening of the eye which helps in the entry of light into the eye. The pupil regulates the amount of light entering the eye.

The opening in the centre of the iris is called a pupil. An iris is a structure inside the eye that provides colour to the eye. It helps in allowing the light to enter the eye so that it can fall on the retina so that we can see the object.

The pupil inside the eye is perfectly round in shape and exactly equal in size. The light which passes through the pupil and falls on the retina gets completely absorbed by the retina so the pupil is black in colour.

The cataract condition can also be detected if the pupil is either cloudy or pale in colour. This is because the lens is present behind the pupil inside the eye which gets clogged or opaque during a cataract. The normal colour of the eye can be restored if the cataract has been treated completely through the help of an Intraocular lens which replaces the cloudy or opaque lens.

The pupil can also change its colour i.e, it can appear red in colour in some photos due to light produced by flashlight while taking a photo. The appearance of red eyes depends on the side of the gaze while taking a photo.

Functions Of Pupil

The iris and pupil work in coordination to check the amount of light entering the eye. It acts as the aperture from where the light enters the eye and the iris as the diaphragm which controls the light by changing the size of the aperture.

Its size is maintained by a set of muscles that is present in the iris. To check the size of the aperture, one muscle reduces the size and another one increases the size. This is also called construction and dilation of the pupil.

The entry of how much light inside the eye through the aperture is controlled by this process of iris muscles.

The constriction of the pupil is required during bright conditions when too light is present. This light can affect the eye by increasing glare inside the eye and can also cause damage to the retina as well as the lens.

The dilation is required when is not much light in the surroundings so that objects can be seen in such conditions also to improve the night vision of the retina.

Size Of The Pupil

The size is different in different people ranging in various age groups. In children, the pupil size is large and also in young people. In elderly people, the pupil is small in size. The people can also have large as well as small pupils.

The pupil size of a normal person is also different in different light conditions such as in bright environments, the size can be about 2 to 4 mm and in dark conditions, the pupil size can be 6 to 8 mm.

The accommodative pupillary response is a condition that is seen while focusing on a near object, the size of the pupil decreases and constricts its size.

Conditions That Affect Pupil

  • Adle’s syndrome:

The pupil In this case has no responsibility towards the light and shows no reaction towards the light. This affects a single eye, not both eyes. The affected pupil has an increased size than the normal pupil. The cause of this syndrome is still unknown but it is believed to be caused by trauma or ischemic condition (lack of blood). This condition has a slow response to accommodation.

  • Argyll Robertson Pupil

This condition also shows no response towards the light. This condition usually affects both the eyes and decreases the size of the pupils into really small so that they do not react with the light and show any response.

The cause of this condition is unknown and is seen rarely among people and is believed to have an association with diabetic nephropathy and also with syphilis.

  • Relative afferent pupillary defect (RAPD)

This is also known as Marcus Gunn pupil. This is caused when there is damage in the posterior region of the optic nerve and any kind of severe retinal disease. This can be diagnosed by performing a swinging flashlight test in which the person suffering from this kind of condition shows less constriction of the pupil than the normal one when the light is swung from unaffected to affected eye while testing the eye. It affects a single eye in a person. The affected eye appears to dilate in the test.

  • Trauma

The abnormalities in shape and sizes in the pupil due to traumatic conditions is seen. The penetrating eye trauma to the iris inside the eye is a common cause for pupil size changes.

This condition can also occur as a result of complications in cataract surgery or intraocular surgery. However, in trauma, the light responses and the accommodation to light are normal or nearly normal.

  • Sexual Arousal

In this case, pupil dilation is seen which is confirmed by recent researches. This can help in the evaluation of sexual orientation in sexuality research.


The pupil is tested by the eye doctor with the help of a routine eye examination.

In testing, the person is made to sit in a dim-lit room. By placing your gaze on a distant object, the examiner or doctor flashes a small flashlight inside the eye for few times. During this process, the response is observed and noted down.

In Swinging Flashlight test i.e, also called Marcus Gunn test. The flashlight is swung from one eye to another eye to see the responses of the pupils in both eyes.

The response is normal when the light is directly flashed or indirectly flashed into the eye with the help of a flashlight. The response shown by an eye that has the direct effect of light is called a direct response and the effect of another pupil is called a consensual response.

To test the accommodative response of it, the examiner can turn on some of the lights in the room and allows to focus on a particular object and moves it close to the eye.

If it can not dilate in dim light and does not constrict in bright environments it is considered as abnormal i.e, a problem is present in the pupil. If this condition is not abnormal and shows complete normal functioning and appearance also then it is certified by an acronym which is used for such pupils which is called as PERRLA which means pupils are equal, round and are reactive to light and accommodation.

The pupil is an important structure inside the eye and has a vital role in the eye functioning because it allows the light to enter into the eye.

The best way to treat your eyes is to visit your eye care professional and get your eyes checked regularly. He will be able to assess the best method of treatment for your eye ailment. Visit our website Eyemantra. To book an appointment call at +91-8851044355. Or mail us at eyemantra1@gmail.com. Our other services include Retina SurgerySpecs RemovalCataract Surgery, and many more.

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