![]() ![]() Fibers originating from the nasal neuroreceptor cells decussate in the optic chiasm to the opposite optic tract, whereas the temporal fibers continue in the homolateral optic tract. Considerable evidence exists that the visual cells of the retina, that is, the rods and cones, also serve as light receptors controlling pupillomotor activity. The pupillary light reflex arc begins in the retina ( Figure 58.1). The iris dilator fibers contain α-adrenergic sympathetic receptors that respond to changes in sympathetic tonus and changes in the blood level of circulating catecholamines. The size of the pupil is controlled by the activities of two muscles: the circumferential sphincter muscle found in the margin of the iris, innervated by the parasympathetic nervous system: and the iris dilator muscle, running radially from the iris root to the peripheral border of the sphincter. Record these data so that they are easy to read and recall. Next, look at the amount of pupillary constriction that occurs when the patient is forced to focus on a near object, such as a thumb held 15 to 20 cm above the eyes. Slowly move the light up to the patient's eye level and check the pupillary response to the bright light on each side several times. To assess pupillary size in a darkened room, illuminate the face from below. For the same reasons, try not to startle or touch patients with your hands or instruments, as psychosensory stimulation induces mydriasis, hippus, and relatively hyperactive pupils. Patients should be encouraged to fixate visually on a distant object, because if they inadvertently look at your nose or the flashlight, the attempt to converge will reflexly evoke miosis, and certain signs may be overlooked (e.g., anisocoria, light-near dissociation, or a subtle Marcus Gunn sign. Because these phenomena are best tested with the pupils in a semidilated state, clinical observations should be made in a dimly lighted room. Though opioid drugs tend to be among the most common that affect pupil constriction, other medications may also have an effect on the pupils’ ability to dilate.The examiner first must check the size, shape, equality, and position of the pupils, and their response to a bright light. Non-Opioid Drugs That Can Cause Constricted Pupils Illegal forms of opioids or opiates include: During use, opioids tend to stimulate the parasympathetic nerve and cause constricted pupils. Generally, drugs classified as opioids will constrict pupils when the drug is ingested. Generally, stimulants dilate pupils and depressants (like opioids) cause constricted pupils. But substance use and abuse can affect the central nervous system and interfere with the ability of the eyes to react appropriately. Usually surrounding light causes stimulation of the relevant nerve to dilate or constrict the pupils. Pupils that do not dilate or constrict properly can create, or be a symptom of, serious vision problems. Pupil dilation and constriction is an important function that controls the amount of light that enters the eye and allows a person to see properly. When the sympathetic nerve is stimulated, pupils dilate. Normally, when the parasympathetic nerve is activated, it causes pupils to constrict, or narrow. Pupil constriction and dilation are controlled by the sympathetic and parasympathetic nervous systems in the brain. One of the more noticeable, and uncontrollable, ways is dilated or constricted pupils. Physiological changes in the brain can appear in a variety of ways in the rest of the body. On the other hand, depressants generally inhibit brain activity causing drowsiness, lethargy, decreased heart rate, blood pressure, and a sense of calm. For instance, stimulants tend to affect the brain in a way that increases alertness, energy levels, heart rate and blood pressure. How a particular drug affects the body often depends on the type of drug being used. Motivational Interviewing Therapy Program. ![]()
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