How Healthcare Providers Test Pupil Reflexes

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Your pupils control the amount of light that enters your eyes. Testing the pupils is an important part of a comprehensive eye exam.

The pupils of the eye are controlled by the autonomic nervous system, which also is responsible for other things your body does without you thinking, such as breathing and making your heart beat. If your pupils are not working properly, it could be a sign of problems with your nervous system that could impact the rest of your body.

This article provides information about the role your pupils play in helping you see. It also discusses the tests healthcare providers use to make sure they're working properly.

What Is a Pupil?

The pupil is the area in the center of the iris, the colored part of your eye, that looks like a black circle. The pupil is actually a hole through which light passes to the retina, the light-sensitive layer in the back part of the eye.

Pupil of the eye

Peter A. Kemmer / Getty Images

How the Pupil Works

Similar to the aperture of a camera lens, which allows you to adjust how much light is let into the camera, the pupils in the eye expand to be become larger (dilate) or contract to become smaller (constrict). This happens automatically when muscles in the iris respond to outside stimuli.

In bright light, the pupil constricts to reduce the amount of light entering the eye. In dark or dim light, the pupil dilates to allow more light into the eye to improve vision.

The pupil is controlled by a very long nerve pathway in the body. It starts in the brain, then travels down the spinal cord, up over the top of the lung, and eventually makes its way to to the pupil. Any interruption along this pathway could possibly affect this nerve and cause changes in how your pupils react.

Examining Your Pupils

When your healthcare provider examines your pupils, they will first look for anisocoria. This is a condition in which your pupils are different sizes.

Anisocoria affects 20% of the general population and usually does not signal anything abnormal. In some cases, however, unequal pupil sizes can be a sign of serious disease.

Your healthcare provider will also look at the size and shape of the pupil in both bright light and dim light. The speed and quality of your pupil's response to stimuli may also be noted.

They may also test your pupil's reaction to close-up stimuli like small print.

Eye doctors use three tests to assess pupil reflexes: the light response test, the swinging flashlight test, and the near response test.

Light Response Pupil Test

The light response pupil test assesses the reflex that controls the size of the pupil in response to light.

Your healthcare provider dims the lights and asks you to look at an object in the distance. A light is shone into your eyes from each side.

The practitioner watches your pupils closely to determine whether or not your pupils shrink in response to the light. They will also note the size and shape of your pupils.

Swinging Flashlight Pupil Test

The swinging flashlight pupil test is used to compare your pupils' response to light.

Similar to the light response test, the lights in the room are dimmed and you are asked to look at a distant object. This time, your healthcare provider swings a light from one eye to the other to see how each pupil responds.

Each of your pupils should constrict or stay the same size when the light shines on them. The response in each eye should be about the same.

Abnormal responses to this test could be a sign of an afferent pupillary defect (APD), such as Marcus Gunn pupil. This can indicate a problem with the optic nerve or a neurological problem.

Near Response Pupil Test

The near response pupil test is performed less often than the other two tests, but it can be especially important when it is used. This test measures the pupil's response to something close up vs. farther away and can help rule out certain diseases or conditions.

This test is performed in a room with normal lighting. Your healthcare provider asks you to look at a distant object, then moves a small object or card in front of your eyes.

Your provider watches your pupils closely to make sure they constrict quickly as your fixation changes from far to near.

Summary

Regular eye exams are important to maintain healthy sight. As part of your examination, your healthcare provider will look at all parts of your eye, including the pupil.

Simple tests, such as the swinging flashlight test can provide key information about your eye's function and your overall health.

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5 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. American Academy of Ophthalmology. Pupillary Examinatiion.

  2. Szabadi E. Functional organization of the sympathetic pathways controlling the pupil: light-inhibited and light-stimulated pathwaysFront Neurol. 2018;9:1069. doi:10.3389/fneur.2018.01069

  3. Gross JR, McClelland CM, Lee MS. An approach to anisocoriaCurrent Opinion in Ophthalmology. 2016;27(6):486-492. doi:10.1097/icu.0000000000000316

  4. Tomy R. Pupil: Assessment and diagnosisKerala Journal of Ophthalmology. 2019;31(2):167. doi:10.4103/kjo.kjo_48_19

  5. Broadway DC. How to test for a relative afferent pupillary defect (RAPD)Community Eye Health. 2012;25(79-80):58-59. PMID:23520419

Additional Reading
  • Levin, Leonard A. and Anthony C. Arnold. Neuro-ophthalmology: The Practical Guide. Medical Publishers, Inc.