What Does PERRL Stand For?
PERRL stands for "Pupils Equal, Round, Reactive to Light." This is a standard clinical acronym used during neurological and ophthalmological examinations to document normal pupillary findings 1, 2.
Components of the PERRL Examination
The acronym breaks down into four key assessment elements that should be systematically evaluated:
Pupils Equal
- Both pupils should be the same size when measured in dim lighting conditions 2, 3.
- Anisocoria (difference in pupil size) greater than 1 mm is clinically significant and warrants further investigation 2, 3.
- In older adults, pupils may measure 2-3 mm even in dim lighting due to age-related miosis, which is a normal finding 2.
Round
- Pupils should have a circular shape 1, 2.
- Irregular pupil shape may indicate structural abnormalities of the iris or other ocular pathology 1, 3.
Reactive to Light
- Both pupils should constrict equally when exposed to light 1, 2.
- The pupillary light reflex results from parasympathetic innervation via cranial nerve III to the iris sphincter muscle 4, 5.
- Pupils reactive to light 12-24 hours after return of spontaneous circulation (ROSC) are associated with improved survival outcomes in pediatric cardiac arrest patients 1.
Additional "L" Component
- Some clinicians extend the acronym to PERRLA, where the "A" stands for "Accommodative" (pupils constrict during near focusing) 2.
- Near reflex during accommodation causes physiologic pupillary constriction, which should not be confused with pathologic findings 2.
Clinical Examination Technique
Perform the assessment in a darkened room with the patient fixing on a distant target to eliminate the near reflex 6:
- Shine a bright penlight directly into each eye for less than 5 seconds 6.
- Observe for immediate pupillary constriction (direct response) 2, 6.
- Observe the opposite pupil for constriction (consensual response) 4.
- Assess both pupil size and symmetry of response 1, 2.
Critical Clinical Distinctions
Do Not Confuse Anisocoria with RAPD
- Anisocoria refers to difference in pupil size 2, 3, 6.
- Relative afferent pupillary defect (RAPD) refers to difference in pupillary response to light, detected by the swinging-light test 2, 3, 6.
- These represent entirely different pathophysiologic processes and require separate evaluation 3, 6.
Confounding Factors
- Sedation, potent analgesics (especially opioids), and neuromuscular blockade significantly confound pupillary assessment 1, 2, 6.
- Pupillary evaluation in infants and children may be challenging due to frequent fixation shifts and physiologic pupillary oscillations (hipus) 2, 6.
Clinical Significance
Prognostic Value
- Pupillary light responses are strong predictors of neurological outcome and should be integrated with consciousness scales like the Glasgow Coma Scale 2.
- Serial assessment of pupillary light response is integral in critically ill patients, as preserved responses may be associated with improved neurological outcomes 2.
Red Flags Requiring Urgent Evaluation
- Unilateral dilated pupil with poor reactivity suggests third nerve palsy or uncal herniation 1, 3.
- Bilateral fixed, dilated pupils indicate severe brainstem dysfunction 1.
- RAPD of 0.3 or more log units is not typical in amblyopia and should prompt investigation for optic nerve or retinal pathology 2, 6.