Pupil testing typically is a quick diagnostic procedure conducted by either an eye care provider or, more commonly, a technician. It usually involves swinging a pen light from eye to eye to assess both the direct and consensual pupillary response. For some clinicians, this can be both difficult and frustrating. However, if performed diligently, pupil testing can save a patient’s sight––or life.
Pupil Testing 101
Under normal circumstances, light entering either eye elicits the exact same pupillary response. But if, for example, there is a lesion in the patient’s right optic nerve or retina, light directed to that eye will not yield a normal response in either pupil.
Interestingly, however, when light is shined in the patient’s healthy contralateral eye, both the left and right pupils will react normally and consistently.1 Such an obvious difference in pupillary response points to a right eye abnormality, such as optic neuropathy.
Screening for Neuro-Ophthalmic Disorders
• Horner’s syndrome. During pupil testing, anisocoria (a difference in pupil size) is important to measure because it can reveal an underlying problem with the afferent pupillary pathway. Such a finding can help uncover the existence of a lesion located along the pathway of either the supply from the Edinger-Westphal nucleus to the sphincter muscle of the iris (Adie’s pupil), or the ocular sympathetic supply to the dilator pupil muscle of the iris (Horner’s syndrome).
Keep in mind that a physiological anisocoria is a harmless condition, whereas Horner’s syndrome can be indicative of several potentially fatal conditions, including stroke, a cancerous tumor of the lung apex (pancoast tumor), a tear in the carotid artery’s endothelium or a spinal cord injury.2-6
Because Horner’s syndrome affects the sympathetic nerves, patients typically present with a smaller pupil, a ptosis and a lack of sweating on the affected side of the face (also known as the classic triad of meiosis, ptosis and anhydrosis).7
• Third nerve palsy. This is another significant condition that may be detected via pupillary testing. In this instance, patients typically exhibit a dilated or “blown” pupil as well as ptosis. Take note, however, that a third nerve palsy can occur with little to no pupillary involvement.8 Nevertheless, such a presentation typically restricts extraocular motor functioning.
Third nerve palsy is a medical emergency that warrants immediate imaging to rule out associated conditions, such as a cerebral aneurysm, compressive mass or even multiple sclerosis. In fact, if a third nerve palsy is noted––either with or without a history of trauma––immediate referral to an emergency room is required.9,10
• Neurosyphilis. One additional condition to screen for via pupillary testing is neurosyphilis, which can cause severe vision and hearing loss, psychiatric complications and even death.11-13 One particular ophthalmic finding often can help you confirm the final diagnosis of neurosyphilis––an Argyll Robertson pupil.
The best way to remember this testing approach is to create an acronym using the first letters of each word in “Argyll-Robertson pupil:”
- ARP: Accommodative Response Present.
Then, simply invert the acronym:
- PRA: Pupillary Response Absent (to light stimulus).
A patient with a positive Argyll- Robertson finding will exhibit a small pupil that constricts poorly to direct light, but briskly when a near target is presented.14 The moment you confirm this diagnosis, refer the patient to an infectious disease specialist for appropriate laboratory testing and treatment before further morbidity occurs.
Pupil Testing for Glaucoma?
Because the condition typically presents as an asymmetric neuropathy, pupillary testing potentially could be used to detect glaucoma. In fact, one study showed that pupil testing could help reveal photosensitive ganglion cell damage associated with glaucoma.15
So, why is pupil testing not routinely included in a glaucoma work-up? One primary reason is that pupillary response frequently would be too subtle during the earliest stages of disease. Also, the swinging flashlight test is difficult to perform accurately on patients with dark irides.
However, advanced pupillary testing devices such as RAPDx (Konan Medical) could help eye care practitioners more accurately diagnose conditions that yield a relative afferent pupillary defect (RAPD), including glaucoma.15,16
RAPDx measures pupillary responses to direct and consensual light and accommodation while the patient looks at a series of color illuminations. The direct and consensual response is plotted on a graph, so you can easily determine the extent of RAPD present.
Pupil screening is one of the most infrequently applied diagnostic tests, because it is difficult to perform and challenging to interpret. Still, you simply cannot afford to discount its diagnostic and prognostic value when evaluating patients for sight- and life-threatening neuro-ophthalmic disorders.
Dr. Karpecki is a paid consultant to Konan Medical. Neither he nor Dr. Shechtman has direct financial interest in any of the products
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