![]() Delta-9-tetrahydrocannabinol (THC), also known as the cannabis and marijuana, rapidly distributes from blood and can cause various effects on pupil size. It is known that sedatives, anesthetics, psychostimulants, as well as opioids and cannabinoids, have different effects on pupil diameter. ![]() This affect the pupil diameter due to the presence of both adrenergic and serotergic receptors in the retina, as well as the multiple complex pathways in the central nervous system. Although the sympatheticparasympathetic activation cycle is regulated regularly under physiological conditions, it can be affected by any pharmacological agent that affects this cycle. Roughly, the stimulus from the periphery moves to the spinal cord, brain stem, hypothalamus and eventually to the cerebral cortex, respectively. The sympathetic and parasympathetic system has a hierarchical order. Miosis occurs when the parasympathetic system is activated and mydriasis occurs when the sympathetic system is activated. Pupillary diameter control is mainly achieved by autonomic control, in which the sympathetic and parasympathetic system plays a role. In addition, many different factors such as age, attention level, changes in parasympathetic and sympathetic efferent pathways and tonus dominance affect pupil diameter. The most important factors affecting the pupil diameter are the intensity of light reaching the retina and accommodation. Any pathology that may develop in the arch of the pupil reflex disrupts the pupil’s response to light. ![]() Īpart from the function of controlling the size of the pupil, the iris that has sympathetic and parasympathetic innervation contributes to the reduction of aberrations and the depth of focus. In infants, the pupil is smaller and reaches its normal diameter at the age of 7–8, and tends to be smaller in the elderly. At maximum constriction the fibers of the sphincter pupillae are shortened by 87% relative to their length in the resting state, a property possessed by no other smooth muscle in the human body. This means that the area of the pupil (πr2), and thus the amount of light admitted to the eye, can vary by a factor of 36. The pupil ranges in size from 7.5–8 mm at full mydriasis to 1.5–2 mm at full miosis. This adjustment is effected by a muscle system composed of a circular part, the sphincter pupillae, and a radial part, the dilator pupillae. The main function of the iris is to regulate the amount of light reaching the retina, which it does by constantly adjusting the pupil size. A colored circular muscle, the iris, is perforated by a central opening, the pupil, which is shifted slightly toward the nasal side.
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