Pupil: Examination Methods

Examination Methods

Complete examination of the pupilincludes testing direct and indirect light reflexes, the swinging flashlight test, testing the near reflex, and morphologic evaluation of the iris. A synopsis of all findings is required to determine whether a disorder is due to ocular or cerebral causes .

Testing the Light Reflex (Table 9.1)

Light reflex is tested in subdued daylight where the pupil is slightly dilated.

The patient gazes into the distance to neutralize near-field miosis.

Direct light reflex: 

The examiner first covers both of the patient’s eyes, thenuncovers one eye. Normally the pupil will constrict after a latency period of about 0.2 seconds. The other eye is tested in the same manner.

Indirect or consensual light reflex: 

The examiner separates the patient’seyes by placing his or her hand on the bridge of the patient’s nose. This pre-vents incident light from directly striking the eye being examined, which would elicit a direct light reflex. The examiner then illuminates the other eye while observing the reaction of the covered, non-illuminated eye. Normallyboth pupils will constrict, even in the non-illuminated eye.

Swinging flashlight test: 

This test is used to diagnose adiscrete unilateral orunilaterally more pronounced sensory deficit in the eye (optic nerve and/or ret-ina). Often damage to the optic nerve or retina is only partial, such as in partial atrophy of the optic nerve, maculopathy, or peripheral retinal detachment. In these cases, the remaining healthy portions of the afferent pathway are suffi-cient to trigger constriction of the pupil during testing of the direct light reflex. This constriction will be less than in the healthy eye but may be diffi-cult to diagnose from discrete pupillary reflex findings alone. Therefore, the reflexive behavior of both eyes should be evaluated in a direct comparison todetect differences in the rapidity of constriction and subsequent dilation. This is done by moving a light source alternately from one eye to the other in what is known as a swinging flashlight test.

Reproducible results can only obtained if the examiner strictly adheres to this test protocol:

❖The patient focuses on a remote object in a room with subdued light. This neutralizes convergence miosis, and the pupils are slightly dilated, making the pupillary reflex more easily discernible.

❖The examiner alternately illuminates both eyes with a relatively bright light, taking care to maintain a constant distance, duration of illumination,and light intensity so that both eyes must adapt to the same conditions.

❖The examiner evaluates the initial constriction upon illumination and the subsequent dilation of the pupil. 

Where the pupil constricts more slowly and dilates more rapidly than in the fellow eye, one refers to a relative afferent pupillary defect. The defect is “rela-tive” because the difference in pupillary reflex only occurs when there is a difference in the sensory defect to the left and right eyes.

Evaluating the Near Reflex

The near reflex triad consists of:

1. Convergence of the visual axes.

2. Accommodation.

3. Constriction of the pupils (miosis).

The near reflex is tested by having the patient focus on a distant object and then on an object in the near field. Usually this is the patient’s finger, which is brought to within 10 cm of the eyes. The near reflex is intact if both eyes con-tinuously converge with accommodation and miosis appropriate for the patient’s age as the object is moved to within 10 cm of the eyes. The examiner should take care to avoid illuminating the pupil, which will produce a light reflex with miosis.