The first step in the pupillary examination is to determine if anisocoria is present, which may not be as easy as it sounds. If you do not detect anisocoria in bright illumination, test for it in semidarkness, observing the other conditions for correct pupil testing. A carefully taken history may explain this pupil abnormality. Eye drops, trauma, or neck operation that has injured the sympathetic chain may produce anisocoria.
The mechanics of testing are not difficult, but they must be scrupulously employed. Do not stand in front of the patient and do not shine the light directly at the patient. Stand with the light off to one side, and have the patient look off at a distance to eliminate factors that might stimulate accommodation and invalidate the testing. Be sure that the beam of light is small enough that only one eye at a time is stimulated. Check the light reflex several times to be sure that the pupillary contraction is the result of the light and not of physiologic pupillary unrest.
The second step in the examination is comparing the reaction of the pupil to light and accommodation so that you can decide whether it is the larger or the smaller pupil—or whether both pupils are abnormal. Signs of fatigue may be a more subtle indication of a pupillary defect. Fatigue may not be apparent with one testing of the light reflex, and multiple retesting may be of value.
Traumatic mydriasis and iridoplegia can be complete, incomplete, or segmental. The causes of these findings after blunt eye trauma can be multiple. The sphincter can be torn or mechanically stunned. If the trauma is severe enough to cause recession of the angle, branches of the short ciliary nerve may be injured at the iris root. Lastly, retrobulbar hemorrhages may damage the ciliary ganglion or the short ciliary nerves.
The final step, particularly if function is intact and only anisocoria is present, is checking for associated signs, such as ptosis, muscle imbalance, heterochromia, or pupil cycling time.
The pupil cycling time can be determined by focusing a small beam of light, such as a slit lamp beam, at the pupil margin and measuring the average period of pupil oscillations with an infrared video pupillometer or a stopwatch. The clinical usefulness of pupil cycling time versus afferent pupillary defect may not be worth the effort to measure it. Some authors, however, believe that pupil cycling abnormalities indicate specific diseases. For instance, in demyelinating optic nerve disease, pupil cycling may be absent or at least abnormal (i.e., irregular in amplitude or just intermittent), even if there is a normal light response. They feel this abnormality is not seen in normal persons or in other diseases of the optic nerve.
Figures 3.1 and 3.2 outline the causes of miosis and mydriasis and provide information in a compact form that will help in the differential diagnosis (Figs. 3.3, 3.4, 3.5).
Figure 3.1 Types and causes of miosis.
Figure 3.2 Types and causes of mydriasis.
Figure 3.3 Approach to pupil evaluation, part 1.
Figure 3.4 Approach to pupil evaluation, part 2.
Figure 3.5 Approach to pupil evaluation, part 3.