CHAPTER 10

The Patient With Pupillary Abnormalities

Pupillary function is an important objective clinical sign in patients with vision loss and neurologic disease. In patients with vision loss, an afferent pupillary defect localizes the site of damage to the retina, optic nerve, optic chiasm, or optic tract. Efferent pupillary dysfunction may herald the presence of serious neurologic pathology such as aneurysm or tumor. Pupillary anatomy and innervation are discussed in Chapter 1, and the evaluation of relative afferent pupillary defect is described in Chapter 3. This chapter reviews the clinical approach to patients with pupillary disorders, including irregular pupils, anisocoria, and light–near dissociation.

History

Patients with pupillary disturbances, particularly anisocoria, might not be aware of any abnormality. This is especially true in persons with dark-colored irides. Frequently, a spouse, friend, or physician brings the anisocoria to the patient’s attention. The patient might describe photophobia, difficulty focusing when going from dark to light or light to dark, and blurring of vision.

The clinician should inquire about any new medications, ocular infections, face or neck trauma, headache or facial pain, or change in eyelid position.

Pupillary Examination

Documenting the onset of the pupillary abnormality may be facilitated by careful inspection of previous photographs of the patient, such as old identification cards, a driver’s license, or school and family photos.

A thorough clinical examination of the pupils requires only simple, inexpensive tools: a bright, even, handheld light source (such as a halogen transilluminator); a pupil-measuring gauge, preferably in half-millimeter increments; an examination room in which background illumination is easily controlled; and some topical eyedrops. For information on detecting and measuring afferent pupillary defects, see Chapter 3. 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 darkness and room light. To

avoid accommodative miosis, the patient should fixate on a distant target, and the clinician should be careful not to block the patient’s fixation.

To check the pupillary light reflex, briefly shine a bright focal light onto 1 pupil and note the speed and amplitude of its constriction. Most clinicians observe only the illuminated pupil (the direct response) because the consensual constriction of the contralateral pupil is difficult to assess simultaneously. 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 good eye, both the pupil of the good eye (direct response) and the pupil of the blind eye (consensual response) will constrict briskly. In other words, poor vision in 1 eye is never a cause of anisocoria.

In addition, the pupillary near response should be examined. This test should be carried out in moderate room light, such that the patient’s pupils are midsize and the near object is clearly visible. The patient is given an accommodative target with fine detail to look at. Although the near response is usually triggered by blurred or disparate imagery, it has a large volitional component, and the patient may need encouragement. If the patient has not made sufficient effort, “practice runs” may be needed. Often, a good near response is obtained on the third or fourth try. 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 (or the clinician) is not trying hard enough.

Slit-lamp examination of the anterior segment is also an 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, gonioscopy should be performed to rule out angle-closure glaucoma. 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 the oculomotor nerve 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.

When the pupil appears white (leukocoria), the problem is typically a light-reflecting abnormality in the posterior segment. Common causes include persistent hyperplastic primary vitreous, retinopathy of prematurity, or sometimes cataract. About 20% of children with leukocoria have a malignant tumor such as retinoblastoma.

Pharmacologic agents can be used to confirm a clinical suspicion of Horner syndrome, tonic pupil, or pharmacologic mydriasis. It is important to remember, however, that pharmacologic pupillary testing is not infallible and false-positive and false-negative test results can occur. Thus, test results must be interpreted on an individual basis.

Baseline Pupil Size

The resting pupil size is influenced by several factors including ambient light, state of retinal adaptation, level of arousal, and patient age. Pupils, in general, become smaller with age. Sleepiness results in loss of cortical inputs that inhibit the Edinger-Westphal nucleus and thus causes small pupils. Elevated intraocular pressure may result in enlargement of the pupil, possibly due to iris ischemia. Pupils are often dilated after generalized tonic-clonic seizures. Extremely small pupils