Your pupils control the amount of light that enters your eyes. Testing the pupils is an important part of a comprehensive eye exam. Because you do not have voluntary control of your pupils, pupil testing may uncover possible problems with your autonomic nervous system. Eye doctors use three procedures to test pupil reflexes.
1. Light Response Pupil Test
The light response pupil test assesses the reflex that controls the size of the pupil in response to light. Your doctor will first dim the lights, then ask you to look at an object in the distance. A light will be shone into your eyes from each side. Your doctor will watch your pupils closely to determine whether or not your pupils constrict in response to the light, making note of the size and shape of your pupils.
2. Swinging Flashlight Pupil Test
The swinging flashlight pupil test is used to compare your pupils' response to light. The lights in the room will be dimmed, and you will again be asked to look at a distant object. Your doctor will "swing" the light rhythmically from one eye to the other, noting the response of each pupil. Your pupils should constrict or stay the same size when the light is shone on them. Dilating pupils may alert your doctor to a possible optic nerve problem.
3. Near Response Pupil Test
The near response pupil test measures the pupil's response to a near target. This test will be performed in a room with normal lighting. Your doctor will ask you to look at a distant object, then move a small object or card in front of your eyes. As you fixate your eyes on the near object, your doctor will watch your pupils closely to make sure they constrict quickly as your fixation changes from far to near.
Levin, Leonard A. and Anthony C. Arnold. Neuro-ophthalmology: The Practical Guide. Medical Publishers, Inc, 2005.