Chapter 2 Testing of the pupils is an integral part of the complete ophthalmologic and neurologic examinations. Proper understanding of the pathophysiology of the pupillary light and near reflexes requires knowledge of the anatomy, physiology, and pharmacology of the sympathetic and parasympathetic innervation of the eye. A detailed discussion of these systems is presented in the evaluation of patients with anisocoria in Chapter 15. This chapter presents practical information about eliciting the bedside clinical information that facilitates the precise diagnosis of pupillary disorders. Because the control of the pupil size and movement is under the control of the autonomic nervous system, pupil testing gives data about visual function that is outside the voluntary control of the patient. This makes tests of pupil function very useful in assessing the presence of factitious or embellished disorders. The minimal patient assistance needed to perform the pupil examination makes this test especially useful in infants, young children, the elderly, and very ill patients who find it difficult to cooperate for other portions of the examination. The presence of a relative afferent pupillary defect (APD) may be the only sign of a unilateral or asymmetric optic nerve or retinal disorder in such patients. The pupillary light and near responses are dependent on the integrity of complex and widespread components of both the central and peripheral nervous systems. Pupil disorders can be produced by disease from the chest and thoracic spinal cord (e.g., Horner’s syndrome) to the cerebral cortex (e.g., pupillary dilation during partial seizures). By combining pupil findings with other bedside exam findings, the ability to reach a precise anatomic diagnosis is enhanced. Because of the influence of ambient light, fixation distance, emotional state, and other factors such as medications on pupil size and function, it is important to control the testing environment carefully, and to use specific tools in the testing. In bright ambient lighting conditions, the parasympathetic constricting influence of the light reflex usually dominates the normal size of the pupils. In dim ambient light, the parasympathetic outflow to the pupils is reduced, and the sympathetic pupil dilating influence predominates. By noting the absolute and relative sizes of the pupils in these two lighting conditions, it is often possible to decide which pupil is dysfunctional in patients with anisocoria. If pupillary asymmetry increases in bright ambient light, the larger pupil usually demonstrates a defect of constriction (usually a parasympathetic problem), whereas an increase of anisocoria in dim ambient light usually indicates a deficiency of dilation of the smaller pupil (such as from sympathetic dysfunction). The light reflex should be tested while the patient fixates a distant target, to remove the possibility of miosis produced by the near response. When testing the near response of the pupils, a fixation target with visual detail (such as a small picture or text fragment) and appropriate refractive correction help maximize the near effort. The light reflex should be tested with a bright light source that can be manipulated easily. A halogen bulb in an ophthalmoscope or transilluminator is adequate. The light source should have a focused beam so that just one pupil at a time is illuminated at the testing distance. It is important to stimulate each eye along its visual axis if there is any misalignment of the eyes. The size of the pupils should always be estimated using a pupil gauge, such as that often provided on near vision acuity cards. It is important to remember that the area of the pupil changes proportionate to the square of the diameter, so the apparent size of a pupil is nonlinear with respect to the diameter. For this reason, it is important to measure the pupils accurately and not rely on estimation. Placing a graded neutral density optical filter in front of one eye reduces the intensity of the light falling on the retina by a known amount. This reduces input to the pupillomotor centers from that eye, similar to the effect of a retinal or optic nerve lesion of that eye. Placing the appropriate-strength neutral density filter before the unaffected eye balances the afferent pupillary defect of the affected eye, and thereby can be used to measure the severity of an afferent pupillary defect. Filters are readily available in 0.15 and 0.3 log unit strengths from photographic supply stores, or in a testing bar with several filters in a row. Although routinely available only to the ophthalmologist, neuro-ophthalmologist, or optometrist, the slit-lamp biomicroscope is a valuable tool in the evaluation of pupil disorders, by allowing observation of phenomena such as traumatic iris tears, synechiae, and the segmental contraction of the pupil border seen in Adie’s tonic pupil syndrome. The use of selected agents can help elucidate the cause of abnormal pupil responses. Ophthalmic drops that are useful for diagnosis are cocaine 10%, hydroxyamphetamine 1%, and pilocarpine 0.1% and 1%. In most people, the pupils are roughly circular, located slightly inferiorly and nasally within the corneal window. Slightly elliptical pupils can be normal. When there is a definite abnormality of pupil shape, it should be measured in its longest and shortest dimension and recorded. A drawing or photograph may be helpful for longitudinal assessment. A common cause of irregular pupil shape is prior trauma, uveitis, or surgery, especially cataract surgery. These pupils may also have altered motility due to disruption of the iris musculature. Congenital iris coloboma usually produces a lifelong inferior or inferonasal pointed appearance to the pupil. Iris coloboma may be isolated or part of a more generalized ocular dysgenesis syndrome. Transient change of the pupils to an elliptical or “peaked” shape may occur as the “tadpole pupil” associated with sympathetic hyperactivity and migraine (see Chapter 15). In acutely ill patients with midbrain dysfunction, elliptical pupils may occur unilaterally or bilaterally, sometimes called corectopia. The pupils associated with Adie’s tonic pupils are often somewhat irregular in shape, due to asymmetric, segmental contraction of the pupil constrictor smooth muscle. Record the size and shape of the pupils in dim and bright ambient light. The size of each pupil should be estimated in both lighting conditions with a pupil gauge.
PUPIL TESTING
THE IMPORTANCE OF PUPIL TESTING
OBJECTIVE TEST
MINIMAL PATIENT COOPERATION REQUIRED
HELPFUL IN NEUROLOGIC LOCALIZATION
TESTING PARAMETERS AND TOOLS
CONTROL OF AMBIENT LIGHT
CONTROL OF FIXATION DISTANCE
BRIGHT LIGHT SOURCE
PUPIL SIZE GAUGE
NEUTRAL DENSITY FILTERS
SLIT-LAMP BIOMICROSCOPY
PHARMACOLOGIC TESTING
PUPIL SHAPE
RESPONSES TO MANIPULATION OF AMBIENT LIGHT
PROCEDURE
INTERPRETATION
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