The pupil is the round hole in the center of the iris. The diameter of the normal pupil varies with the intensity of light, generally about 2 mm for newborns and the elderly, and 4 to 5 mm for adults. in natural light, when the pupil is <2 mm in diameter, the pupil is narrowed, and when it is >5 mm, the pupil is dilated. Pupillary abnormalities refer to abnormalities in pupil size, position, shape and reflex to light. There are two types of smooth muscles in the iris: the circular muscle surrounding the pupil is the pupillary sphincter, and the radially straight one is the pupillary dilator, which is innervated by the parasympathetic and sympathetic nerves, respectively. Pupillary light reflex: Light stimulates the retina, and nerve impulses travel through the optic nerve, optic cross, optic tract, lateral geniculate body, to the anterior parietal nucleus, then around the midbrain conduction duct to the bilateral E-W nucleus (part of the nucleus accumbens), and through the parasympathetic efferent pathway to the pupillary sphincter and ciliary muscle, causing pupillary constriction. The retinal excitation is transmitted through the optic nerve to the occipital cortex, then to the posterior oculomotor center of the frontal middle gyrus, and through the cortical medullary tract to the E-W nucleus, from which fibers are sent via the motor nerve to the bilateral medial rectus muscle, resulting in inversion of the eye; at the same time, parasympathetic fibers are sent to the pupillary sphincter, causing constriction of the pupil. Diagnosis and Differential Diagnosis] I. Iris Anomalies 1. Congenital Iris Anomalies (1) Congenital absence of iris. The iris is absent after birth, and the pupil is as large as the corneal limbus, often combined with glaucoma, cataract, and ocular tremor. (2) Iris defect. This is a defect of varying size in the lower part of the iris, with the tip of the iris shaped like a melon facing outward, often combined with a choroidal defect. (3) Small pupil. The pupil is about 1 mm in diameter and is often ineffective with dilating agents. (4) Multipupillary disease. In addition to the pupil, there are several cavities in the iris, and each pupil has its own sphincter. 2. Acquired iris abnormalities (1) Iris atrophy. The iris is locally grayish in color and the normal texture disappears. It is seen in herpes zoster, tuberculosis, etc. (2) Post-iris adhesions. Inflammation causes the iris to stick to the lens, resulting in irregular pupil shape and iris atrophy. If the lesion is between the pupillary reflex center (E-W nucleus) and the ciliary ganglion, the pupil is moderately dilated; if the lesion is in the path after the ciliary ganglion, the pupil is extremely dilated. Their main etiologies are traumatic brain injury, vascular disease, inflammation, tumors, and congenital disease. 1. Actinic nerve palsy. All or some of the following manifestations may be present: ptosis of the affected eyelid, impaired upward, downward, and inward movements of the eye, pupil dilatation of varying degrees, diminished or absent light response, and impaired regulatory reflexes. 2. Myotonic pupil. Also known as Adie pupil, when combined with loss of tendon reflex, it is called Adie pupil syndrome. It is characterized by dilatation of one side of the pupil (the left side is more frequent) and loss of direct and indirect light reflexes. The pupil may be reduced with epsilon or 2.5% acetylcholine drops, and may be combined with abnormal sweating, tachycardia, and other autonomic symptoms. It is more common in young women. 3. Periodic motoneural palsy. There are congenital (onset at age 2 or adolescent) and acquired. It is characterized by periodic episodes and transient motoneural palsy. Spasmodic pupillary dilation is caused by excessive sympathetic nerve hyperfunction or lesions in the conduction pathway from the cervical sympathetic ganglion to the pupillary dilation muscle. It is mainly seen in cervical medullary tumors, trauma, cremasteric cavernosa, cervical sympathetic neuritis, pneumonia, mediastinal tumors, and goiter. Clinical manifestations: pupil dilatation; pupil change after application of 1% cocaine and acetylcholine drops (normal pupil or paralytic pupil dilatation can be contracted after medication); pupil narrowing can occur after stellate ganglion block; primary lesion manifestation. Fourth, paralytic pupillary constriction is mostly caused by loss of pupillary opening function after cervical sympathetic nerve paralysis. It is mainly seen in brainstem tumors or inflammation, cervical medullary tumors, cremaster medullary cavitation, dorsolateral medullary syndrome, cervical ribs, cervical sympathetic ganglion after closure, cervical spondylosis, cervical sympathetic neuritis, trauma, pneumonia syndrome, and surgical injury to the thyroid gland. Clinical manifestations: Horner syndrome with small pupils (<2mm) on the affected side, mild ptosis of the upper lid, mild inward sunken eyeballs, and absence of sweating and vasodilation on the face and neck (except forehead). Depending on the location of the lesion, it may be associated with: 1. lower cervical medulla, neck pain, vasomotor dysfunction of the upper extremities, and muscle atrophy of the hands; 2. higher cervical medulla, quadriplegia, and whistling difficulties; 3. upper mediastinum, dry cough, chest pain, shoulder and neck pain, hoarseness, and tracheal displacement; 4. brainstem, cranial nerve and conus crossbundle paresis. V. Spasmodic pupillary constriction (a-lo pupil) Due to parasympathetic nerve and its central excitation, mainly seen in brainstem inflammation, vascular lesions, trauma, tumors and multiple sclerosis. Clinical manifestations: 1, mostly bilateral small pupils (2-3 mm) with untidy and unrounded pupil margins; 2, loss of direct and indirect light responses; 3, presence of the modulation reflex; 4, dilating agents causing only mild dilation; 5, manifestations of the primary lesion.