A comprehensive understanding of a quick yet thorough pupillary exam is essential, because recognition of abnormal pupillary findings may be the first sign of an underlying or impending serious neurologic condition. Reliable automated measurement of pupils, or pupillometry, is now commonly utilized in intensive care settings because abnormal changes in pupil reactivity may be an early indicator of elevations in intracranial pressure (ICP).¹

Some clinicians often reflexively write the acronym “PERRLA” as shorthand for the pupils being equally round and reactive to light and accommodation without too much thought about the localization of the accommodation. When you observe pupils that do not react to light, but do react to near response, that is termed “light-near dissociation.” Conditions with light-near dissociation that more commonly present in the emergent setting will be discussed in the “Differential Diagnoses” section.

Every pupil exam begins with inspection. An estimate of pupillary size in both eyes can be done quickly with direct visualization. Pupillary size is often difficult to gauge, so use of a pocket eye chart is helpful to document (in mm) the size of the pupil in bright and dimly lit settings. Specific care should be taken to identify the shape of the pupils and, potentially, any difference in size. Any potential pupillary shape that is not round should warrant further investigation with a slit-lamp evaluation.³

The examination of the pupil’s reactivity to light should be evaluated. In a dim setting, direct the patient to look off into the distance to avoid the miosis that occurs with near viewing. Using a bright flashlight, observe the direct response of the pupil to the light and repeat with the fellow eye. Observe the consensual response of each eye. The briskness of the pupils’ reactivity to light should be noted (3+ normal brisk reaction, 2+ slightly sluggish, 1+ sluggish). Reactivity to light testing is followed by the swinging flashlight test. The swinging flashlight test is performed by rapidly alternating the light source (1-second intervals) between each eye to assess for a relative afferent pupillary defect (RAPD). The RAPD is detected by an asymmetric pupil response to direct light. In a patient with a RAPD, when the light is swung to the abnormal eye, both pupils dilate owing to less afferent input reaching the midbrain.³ When the light is swung back to the normal eye, both eyes will constrict. This should direct the examiner to consider a unilateral optic nerve or retinal process in the eye that dilates with direct light (Figure 48.2). Less frequently, one can see an RAPD with chiasmal, optic tract, or midbrain lesions. Oftentimes, the RAPD is graded with a numerical system whereby 1+RAPD OD means there is initial constriction, but early redilation of the affected pupil;
2+ RAPD translates to no initial pupil movement, then dilation; 3+ indicates immediate redilation; and 4+ means the pupil is amaurotic (blind).³ A general approach to the patient with anisocoria is outlined in Figure 48.3. Of note, the testing strategies using pharmacologic ophthalmic drops noted in the approach are primarily for reference. The clinical assumption is that the ED or urgent care physician observing these pupillary abnormalities will involve an ophthalmologist or neuroophthalmologist in timely consultation for guidance in diagnosis, management, and treatment of the pupillary abnormalities. Therefore, the management strategies listed in what follows will focus primarily on settings when neuroimaging is considered critical and time sensitive such that delay in recognition may cause permanent neurologic deficits.