Pupil testing is an essential part of a complete eye examination, especially when diagnosing autonomic nervous system disorders that can affect the pupillary response. To document the findings of a pupillary examination, many students and doctors use PERRLA, which stands for: Pupils Equal, Round, Reactive to Light and Accommodation. While this acronym is a great way to remember the parts of the pupil evaluation, because it sounds exactly like a pearl in Spanish making you think of the pupils as the pearls of the eyes, it may be missing a couple of letters that would make the examination results more descriptive and reliable.
A complete pupil evaluation assesses different aspects of the pupil’s function:
Measuring pupil diameter in light and dark conditions
Before testing pupil responses, the pupils should be measured in dim illumination (where the pupils should be larger) and in bright light (where the pupils should be smaller). This is also where the shape of the pupil is assessed and pupil sizes are compared. When measuring in bright light, a transilluminator should be shinning as bright as you can get it and aimed directly at the pupil being measured.
Direct and Consensual responses
This part of the evaluation focuses on the responses of the pupils to light. In the direct response, the transilluminator light is shined on the pupil to observe how that pupil reacts. In the consensual response, a light is shined on one of the pupils, but instead of analyzing the response on the pupil that has the light, you evaluate the contralateral pupil response.
Expected results: the direct response should cause the pupil (on which the light is aimed) to constrict, and the consensual response observed in contralateral pupil (on which the light is not being directly aimed) to also constrict.1
Swinging flashlight test
The Swinging Flashlight test is specifically used to diagnose an Afferent Pupillary Defect (APD). It should be performed in dim illumination. In this test, the examiner shines a light between the eyes for 3-5 seconds and repeats the process for a couple of cycles to see how the pupil reacts when the light is first shinned on it. A bright light shined in one eye should lead to the same amount of constriction in both pupils. The transition from one eye to the other should be quick and accurate so as to maintain the best view of whether or not a pupil size is due to the brief absence of light or to an afferent defect.2
To test the responsiveness of the pupil to a near stimulus, the examiner can hold a near target 10-40 cm from the patient’s eyes and ask the patient to switch between a distance target and the near fixation. When the accommodative response is intact, the pupil should constrict as the patient fixates the near target.1
When only reporting “PERRLA” as our pupillary findings, we miss out on information, like the actual size of each pupil, the speed of pupillary constriction or dilation, and the reaction of the pupil to dark settings.3 While adding these missing factors would certainly distort the convenient PERRLA acronym, there are many instances that recording pupillary findings as PERRLDA-S/B (pupils equally round and reactive to light and dark accommodation, sluggish or brisk reaction) might serve as important for patient care. The additional information could be what helps diagnose a pupillary defect, such as in Horner’s syndrome, where one of the hallmarks is differences in pupil size during dim illumination.
So, during a pupil evaluation, it is good to use PERRLA as our backbone to remember the basic parts. But, it may be a good idea, especially if your demographic tends to skew older in age, to get in the habit of documenting the details that make a difference at the time of diagnosis. You never know when the additional information might save you time and worry.
- Pupillary Examination. American Academy of Ophthalmology; 2020 [cited 2020Jun20]. Available from: https://www.aao.org/bcscsnippetdetail.aspx?id=ce5e4e47-1d5f-4a06-b1c9-22c23879114a
- Broadway DC. How to test for a relative afferent pupillary defect (RAPD). Community Eye Health. 2012;25(79-80):58-9. PMID: 23520419; PMCID: PMC3588138.
- Spector RH. The Pupils. In: Walker HK, Hall WD, Hurst JW, editors. Clinical Methods: The History, Physical, and Laboratory Examinations. 3rd edition. Boston: Butterworths; 1990. Chapter 58. Available from: https://www.ncbi.nlm.nih.gov/books/NBK381/