Three normal pupillary reflexes deserve discussion.
PHYSIOLOGIC PUPILLARY UNREST. This normal pupillary movement goes on constantly, even when the stimulation of the pupil does not vary. The movement varies from very active to barely perceptible. Both extremes may be (and usually are) normal. Abnormally active pupillary movement is said to represent a pathologic state. I have not found the separation of pupillary motion into physiologic movement and hippus valuable or valid.
CILIOSPINAL SKIN REFLEX. This phenomenon is frequently tested, but its mechanism is often misunderstood. Pinching the skin at the neck should dilate the pupils. In the unconscious patient the test is useful for determining the depth of coma and intactness of brainstem pathways. The reflex is mediated by the pain fibers of the descending branch of the fifth cranial nerve and is not (as was once thought) initiated by squeezing the sympathetic chain in the neck.
PUPILLARY LIGHT REFLEX. The degree of pupillary contraction does not always indicate the state of vision. It is not unusual, for instance, for a patient to have finger-counting vision caused by central chorio-retinitis and still maintain not only a good pupillary light reflex but also one that is equal to the reflex pupillary contraction to light of the uninvolved eye. If, however, one pupil is sluggish to light (compared with its fellow eye) but better to accommodation, a defect in the afferent arc of the light reflex is indicated. If the loss of vision is severe enough, an afferent defect or pupillary escape phenomenon may be present.
We are all familiar with the pupil constricting to light and dilating when that stimulus is removed. This phenomenon also occurs physiologically when you go from a lighted environment to a darker one. There are rare cases in which the pupil constricts to darkness. The mechanism is not well understood. This response was first proposed as a sign of retinal disease such as congenital stationary night blindness and congenital achromatopsia. However, it has also been reported in albinism, Best's disease, optic nerve hypoplasia, retinitis pigmentosa, and Leber's congenital amaurosis.
TOURNAY PHENOMENON. The Tournay phenomenon refers to the dilation of the pupil in the abducting eye on sustained lateral gaze. This reaction does not occur immediately, but after a few seconds of sustained gaze. Sharpe and Glaser studied 30 patients, using infrared photography, and found no Instances of the Tournay phenomenon. Loewenfeld, Friedlander, and McKennon, in studying 150 patients, found the phenome-non occasionally and suggested that it may occur in up to 10% of people.