The pupillary light reflex is one of the most important signs in neurology and neurosurgery to assess brain disorders, and in clinical practice the pupillary light reflex can be divided into direct and indirect light reflexes. Loss of direct pupillary light reflex is usually seen in localized eye lesions such as corneal, iris and retinal lesions. If a patient has no visual impairment and simply has a loss of direct pupillary light reflex, it suggests a lesion between the anterior parietal area and the pupillary sphincter. Indirect dysreflexia is usually indicative of a lesion between the nucleus accumbens and the sphincter, with bilateral visual impairment and sensitive pupillary light reflexes being cortical and central blindness. The loss of pupillary light reflex is often used clinically as an important indicator of brain herniation. If a patient is in a coma or has a deepening coma with loss of pupillary light reflex, especially loss of pupillary light reflex on one side, it often indicates brain herniation.