What Is the Pupillary Response?

The pupil is a small round hole in the center of the iris in the eye of an animal or human. It is the channel through which light enters the eye. The contraction of the sphincter of the pupil on the iris can reduce the pupil, the contraction of the pupil dilatator makes the pupil dilated, and the dilation and reduction of the pupil control the amount of light entering the pupil.

[pupil of the eye]

The anterior part of the vascular membrane of the eyeball, the scleral center and the round hole. The smooth muscles arranged in a circle along the pupil are called pupil sphincter. The sphincter shrinks as the pupil shrinks. The smooth muscles arranged radially along the pupil are called enlarged pupil muscles. Dilated pupils when the magnifying muscle contracts. Because the pupils can be dilated or reduced, it can play a role in regulating the amount of light entering the eyeball. Normal pupils can adjust their size reflexively. When light increases, pupils shrink; when light decreases, pupils dilate. If the pupil reflex is abnormal or disappears, it indicates that the regulating function of the nervous system is impaired. Therefore, the clinical use of pupils to reflect light to check the functional status of the nervous system. ^[2]

Pupil size varies with age, race, refractive status, light intensity, target distance, and mood changes. Generally 2 to 5 mm, with an average of about 4 mm.

The pupils of newborns are very small, and they begin to expand only 3 weeks after birth. Young people are older than middle-aged people. In the age of 20-50, pupils are 2 to 3 millimeters in the sun, and then shrink again in old age; hyperopia pupils are smaller, myopia The pupils of the eyes are larger; the whites are slightly larger than the yellows; when the eyes are fixed forward, the pupils are equal or less than 1 mm, and when the two eyes are deflected to the side, the pupils of the turning eyes are slightly larger than the pupils of the turning eyes; Pupils shrink in bright light, larger pupils in the dark; pupils narrower when viewing near objects, and larger when viewing distant objects. Pupil reduction or dilation is limited to 1.5 and 8 mm, and the difference between the eyes is less than 0.25 mm. The dilation and dilation of the pupil are caused by the contraction of the dilator and sphincter (both are smooth muscles). The dilator is radially around the iris. When contracted, the pupil is dilated and the pupil is diminished when it relaxes. The sphincter is at the free edge of the iris. , In a ring shape, shrinks the pupil when contracted, and dilates when relaxed. Both are dominated by sympathetic and parasympathetic nerves, which make pupils dilate or shrink. The dilated pupils are dominated by the cervical sympathetic nerves, and the sympathetic nerve fibers originating in the cerebral cortex enter the dilated pupil center outside the inferior funnel; part of the gray matter fibers that cross the aqueduct of the brain pass through the inner capsule to the ciliary spinal cord center of the spinal cord, which is Budge's In the center (between the neck 6 and the chest 4), the nerve fibers enter the superior cervical sympathetic ganglia, and the postganglionic fibers enter the cranial artery with the internal carotid artery, enter the ophthalmic nerve before the trigeminal ganglion, and then pass through the nasal ciliary nerve and long ciliary nerve. Distributed in the dilated pupils. From the sympathetic nerve suppressing fibers emitted from the hypothalamus to the central Edinger-Westphal nucleus, the sympathetic nerves have an inhibitory effect on the miotic center. For example, during emotional impulses, the pupil can be enlarged through central inhibition. The pupil sphincter is innervated by parasympathetic nerves. The nerve fibers originate from Edinger-Westphal's nucleus inside the midbrain oculomotor nerve nucleus, and the nerve fibers that regulate the reflex nucleus (Perlia's nucleus) enter the orbit in the oculomotor nerve, from the inferior oblique muscle. It is branched off, and 10 to 20 short ciliary nerve fibers are sent forward to the ciliary ganglion into the eyeball, and anastomosis with the ciliary nerve to the pupil sphincter and ciliary muscle. Both muscles have an antagonistic effect and reach an accurate balance under interactive innervation. Therefore, the changes observed clinically can make a localized diagnosis of diseases of the eye and the brain nervous system. In addition, pupil dilation and reduction adjust the light that enters the eye to ensure clear vision. ^[3]

Eckhardt, a professor of psychology at the University of Chicago, has conducted an experiment. During the experiment, he randomly showed some photos to male and female participants, and then observed the changes in their pupils. He found that when women see a picture of a mother holding a child, their pupils dilate by an average of 25%; when men see a nude picture of a woman, they dilate by an average of 20%. The experimental results also show that the size of the human pupil will not only change with the brightness of the surrounding environment, but also be interested and interested in the target.

Cats and foxes have erect pupils

Sheep and goat pupils are laterally slit

The pupils of humans and many animals (except for a few fish) are controlled by the unconscious iris expansion and contraction to adjust the intensity of light entering the eye. This is called pupil reflection. For example, human pupils are large in diameter under strong light

pupil

It is about 1.5 mm and expands to about 8 mm in dim light.

The pupil shape of an animal is determined by the optical characteristics of the vitreous body, the shape and sensitivity of the retina, and the living environment and needs of the species. Usually round or slit-shaped, some aquatic animals have more strange shapes of pupils.

Slit pupils are common in animals moving under different light intensities. In bright light, such pupils shrink into slits, but still allow light to fall on a large part of the retina. The direction of the slit may be related to the direction of movement that the animal needs to perceive with high sensitivity. For example, the domestic cat's pupils are erect, which makes it easier to detect the lateral movement of prey such as mice. Foxes and many snakes are also slit-like pupils.

When taking photos with a flash, the pupils are too late to close in time. The flash illuminates the retina, which is rich in blood vessels, and forms a red-eye phenomenon. The camera with red-eye reduction function pre-flashes the light once, so that the pupil has reached the contraction state when it officially flashes.

Pupil color change and disease

The normal pupil is round, black and transparent, and the sides are about 2.5 mm in diameter. In addition to changes in physiological adjustment, if the pupil diameter is less than 2.0 mm or greater than 5 mm, the edges are irregular, the color is abnormal, and the reaction to light is dull or disappears. And so on, it often indicates the occurrence of some diseases.

Pupils appear white in cataracts, iridocyclitis, glaucoma, eye trauma, high myopia, or systemic diseases such as diabetes. Rufa

Pupil color change and disease

Now that her pupils have turned white, she should go to ophthalmology and internal medicine for detailed examination.

Pupils are often greenish in glaucoma. There is a certain amount of pressure in the normal eyeball. When glaucoma occurs when the intraocular pressure is too high, the pupil can emit a turquoise green reflection due to corneal edema and a series of changes in the eye. Distraught.

Red pupils are common in ocular trauma or certain intraocular bleeding disorders. Depending on the amount of bleeding in the eye, the pupils can take different forms, and vision can also be damaged to varying degrees.

Pupil shape related to predation

Whether an animal is a predator or a predator may determine the shape of its pupils. Researchers analyzed more than 200 terrestrial species, including canines, felines, reptiles, and hooves, and found that shorter ambush predators, such as alligators and foxes, mostly have vertical pupils, Predators such as gazelle and sheep often have horizontal pupils.

The vertical pupil is good for the distance between the eye and the prey. It is very useful for the predator who hides in the shadows and waits for the opportunity, but must hit it immediately. The transverse pupil gives the prey a wide perspective, which is suitable for finding predators that are approaching from various angles. At the same time, herbivores can keep their pupils parallel to the ground by turning their eyes, which also enhances their ability to observe.

The round pupils are mostly owned by predators that track prey, such as cheetahs, or higher ambush predators, such as lions and tigers. Studies have shown that for animals with a shoulder height of 42 cm or more, the vertical pupil loses its advantage. Therefore, the will to survive has helped the tiger, fox, and horse to evolve their pupil shapes that are suitable for their survival . ^[4]