Examination of previous photographs (eg, a driver’s license) may reveal whether the pupillary abnormality was present previously. Clinical examination of the pupils requires a bright, even, handheld light source (such as a muscle light); a pupil-measuring gauge, preferably in half-millimeter increments; and an examination room in which background illumination is easily controlled. Eye drops such as cocaine, hydroxyamphetamine, apraclonidine, or pilocarpine may also be used to help assess the pupils. To evaluate pupil size, the clinician shines a handheld light obliquely from below the nose for indirect illumination and a clear view of the pupils, in both darkness and room light. To avoid accommodative miosis, the clinician asks the patient to fixate on a distant target and takes care not to block the patient’s fixation.
To check the pupillary light reflex, the examiner briefly shines a bright focal light onto 1 pupil and notes the speed and amplitude of the pupil’s constriction. Most clinicians observe only the illuminated pupil (the direct response) because it is difficult to simultaneously assess the consensual constriction of the contralateral pupil. In general, the direct and consensual pupillary responses are symmetric. Thus, shining a light onto a blind eye results in a poor pupillary response in both eyes, but if the light is moved onto the contralateral unaffected eye, both the pupil of the unaffected eye and the pupil of the blind eye (consensual response) constrict briskly. In other words, poor vision in 1 eye is never a cause of anisocoria.
If the light response is abnormal, the pupillary near response should be examined. This test should be carried out in moderate room light so that the patient’s pupils are mid-sized. The clinician directs the patient to look at an accommodative target with fine detail. Although the near response is usually triggered by blurred or disparate imagery, it has a large volitional component, and the patient may need encouragement. Sometimes a better response is obtained if auditory input is added to the visual stimulus, such as a ticking watch, or if a proprioceptive target, such as the patient’s own thumbnail, is used. A lack of near response usually indicates that the patient is not trying hard enough. Light–near dissociation should be diagnosed only when the near response exceeds the best constriction that bright light can produce.
Slit-lamp examination of the anterior segment is another essential part of the pupillary examination. Many ocular lesions can result in miosis, mydriasis, or poor pupillary response. Acute corneal injury or anterior chamber inflammation may explain a small pupil in the presence of ciliary spasm. In a patient with blurred vision, pain, red eye, and a dilated pupil, angle-closure glaucoma should be considered. Transillumination defects of the iris are evidence of iris damage from previous trauma, infection, or inflammation. Sectoral paralysis of the iris sphincter due to tonic pupil or aberrant regeneration of cranial nerve (CN) III is best observed by placing a wide beam at an angle to the iris and turning the light off and on while observing one sector of the sphincter at a time under high magnification. If the irides are intact, an innervational problem should be suspected.
Pharmacologic agents can be used to confirm a clinical suspicion of Horner syndrome, tonic pupil, or pharmacologic mydriasis. However, pharmacologic pupillary testing is not infallible; false-positive and false-negative test results can occur. Therefore, test results must be interpreted on an individual basis.
Excerpted from BCSC 2020-2021 series: Section 5 - Neuro-Ophthalmology. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.