Supratentorial pupillary response

One of the key and most pressing problems of forensic medicine remains the diagnosis of the time since death. Forensic scientists pay no less attention to this problem, which is confirmed by the appearance of new scientific works devoted to establishing the time since death. New methods of diagnosing the time since death at various stages of the postmortem period are being developed, and previously known methods are being modified. The need to continue research, develop new diagnostic methods, and improve old methods is due, in particular, to the existence of different ranges of postmortem periods: supravital reactions; development of early cadaveric phenomena; formation of cadaveric phenomena; development of putrefactive changes and other late cadaveric phenomena up to complete skeletonization of the corpse. Accordingly, principles and methods of diagnosing phenomena that allow establishing the time since death are being developed for each of the specified periods. Analysis of modern scientific research shows that today only the maximum set of data on the time since death can provide a result, the accuracy of which meets the needs of law enforcement agencies.

The most pressing problem remains the determination of the time since death occurred in the early postmortem period, which accounts for a significant portion of corpse examinations at the scene of the crime. After death, organs and tissues may for some time react appropriately to various external stimuli. This phenomenon is called "supravital reactions." During the period of supravital reactions, a gradual, time-determined physiological decline in the viability of individual organs and tissues occurs, irreversible changes develop, and, finally, the death of individual cells (cellular death) occurs as expected; these processes correspond to different time intervals.

The duration of supravital reactions is determined by the type of tissue and a number of external conditions.

Certain possibilities in diagnosing the time of death during the period of supravital reactions are given to forensic practice by the assessment of the pupillary reaction. This reaction consists of the ability of the smooth muscles of the iris to respond to external stimuli by constriction or dilation of the pupil. One of the known methods of identifying this reaction is the effect of a chemical irritant on the smooth muscles of the iris by the action of pharmacological preparations atropine or pilocarpine by introducing them into the anterior chamber of the eye using a syringe with subsequent recording of the reaction time of the pupils - their constriction or dilation. However, the latest works devoted to the study of this supravital phenomenon were published in the 70-80s of the last century.

The aim of our work is to study the features of the anatomical and histological structure of the iris, the sphincter of the pupil and the dilator of the pupil, their physiology from the point of view of the influence of modern pharmacological drugs that regulate the size of the pupil.

It is necessary to dwell separately on the anatomical structure of the eye, namely the iris, and the processes of regulation of the pupil's reaction in a living person. The iris, being the anterior part of the vascular tunic of the eye, has the shape of a disk with a hole in the center and is actually a diaphragm that divides the space between the cornea and the lens into two chambers - anterior and posterior. The volume of the anterior chamber of the eye is on average 220 μl, the average depth is 3.15 mm (2.6-4.4 mm), the diameter of the anterior chamber varies from 11.3 to 12.4 mm. From the side of the anterior chamber of the eye, the surface of the iris is divided into two belts: the pupillary, about 1 mm wide, and the ciliary - 3-4 mm. The iris consists of two layers: mesodermal (anterior) and ectodermal (posterior). The pupil itself is an opening in the center of the iris, through which light rays fall on the retina of the eye. Normally, the pupils of both eyes are round, the size of the pupils is the same. The diameter of the pupil in a living person varies on average from 1.5-2 mm to 8 mm depending on the degree of illumination. Changes in the diameter of the pupillary opening in a living person occur reflexively in response to irritation of the retina by light, during accommodation, during convergence and divergence of the visual axes, in response to other stimuli. By regulating the flow of light entering the eye, the diameter of the pupil becomes minimal in the brightest light and maximal in the dark. In fact, the reaction of the pupil to changes in illumination is adaptive in nature, stabilizing the illumination of the retina, screening the eye from excess light, reflexively dosing the amount of light depending on the degree of illumination of the retina ("light diaphragm"). The change in the size of the pupil is caused by the action of the sphincter pupillae muscle (m. sphincter pupillae), which contracts the pupil narrows, developing miosis, and the dilator pupillae muscle (m. dilatator pupillae), which contracts the pupil dilates, developing mydriasis. The muscles are located in the iris of the eye in the mesodermal layer. In the pupillary belt (zone) there are circularly running muscle fibers that form the sphincter of the pupil with a width of about 0.75-0.8 mm. The sphincter pupillae muscle has a telescopic type of contraction, the muscle cells that make it up correspond to all the criteria of smooth muscles (fusiform) and are oriented parallel to the pupillary edge. The bundles of muscle cells are tightly packed and separated by thin layers of connective tissue. Arterioles, capillaries, sensory and motor nerves are distributed among the bundles of collagen fibers. Nerves do not penetrate deep into the muscle cell group, but are adjacent to its surface. In connection with this relationship between nerves and muscle cells, a number of researchers believe that muscle cell groups form functional units. Apparently, only one cell of a functional unit is innervated,and tight intercellular contacts allow depolarization to spread to other cells. The basal membrane of the sphincter of the iris is no different from the basal membrane of other smooth muscle cells. This membrane comes into contact with collagen fibrils separating muscle groups, between which nerve fibers lie. On individual groups of muscle cells, the nerves form bundles. Usually, a bundle consists of 2-4 nerve axons surrounded by Schwann cells. Axons without a Schwann sheath end directly on the muscle cell. Innervation of the sphincter muscle of the pupil is carried out by parasympathetic nerve fibers (postganglionic fibers) extending from the ciliary ganglion, acetylcholine is released from the endings of the postganglionic fibers, which acts on M-cholinergic receptors. Preganglionic fibers are part of the oculomotor nerve, starting from the pupillomotor neurons of the Yakubovich-Edinger-Westphal nucleus, which are part of the oculomotor nucleus of the brainstem. In the depth of the ciliary zone of the mesodermal layer there is a thin layer with a radial direction of fibers - the muscle - dilator pupillae. Cells of the muscle - dilator pupillae are cells of the pigment epithelium and have the ability to form myofibrils in the cytoplasm, thus combining the characteristics of cells of the pigment epithelium and smooth myocytes. The dilator muscle is innervated by sympathetic nerve fibers, postganglionic fibers extend from the superior cervical ganglion, norepinephrine and a small amount of adrenaline are released from their endings, which act on adrenergic receptors (alpha and beta); Preganglionic fibers originate from the ciliospinal center, located at the level of the eighth cervical, first and second thoracic segments of the spinal cord.thus combining the characteristics of pigment epithelial cells and smooth myocytes. The dilator muscle is innervated by sympathetic nerve fibers, the postganglionic fibers extend from the superior cervical ganglion, from their endings norepinephrine and a small amount of adrenaline are released, which act on adrenergic receptors (alpha and beta); preganglionic fibers extend from the ciliospinal center, located at the level of the eighth cervical, first and second thoracic segments of the spinal cord.thus combining the characteristics of pigment epithelial cells and smooth myocytes. The dilator muscle is innervated by sympathetic nerve fibers, the postganglionic fibers extend from the superior cervical ganglion, from their endings norepinephrine and a small amount of adrenaline are released, which act on adrenergic receptors (alpha and beta); preganglionic fibers extend from the ciliospinal center, located at the level of the eighth cervical, first and second thoracic segments of the spinal cord.

After clinical death, the nervous tissue dies first. The survival time, i.e. the time after which the resumption of blood circulation does not significantly affect the structure and function of the organ, for the brain is 8-10 minutes at a temperature of 37 C0, however, when blood circulation in the body stops, this time period decreases to 3-4 minutes, which is explained by insufficient aeration of the brain due to the weakness of heart contractions in the first minutes after the resumption of blood circulation. Under hypothermia conditions, in individuals trained in relation to hypoxia, the time interval may increase. After this period, the central nervous system can no longer exert any regulatory influence on the pupil muscles. Thus, the lifetime reactions of the nervous system to various types of stimuli that immediately preceded the onset of death, in particular anisocoria, remain fixed and preserved, i.e., in fact, the pupils can posthumously reflect various lifetime lesions of the nervous system. And the eye itself, in particular the pupillary muscles, becomes an autonomous self-regulating structure. After death, after 1-2 hours, the pupil begins to narrow (this is due to the stiffening of the soft muscles of the iris against the background of the predominance of the sphincter of the pupil). Its subsequent expansion is not observed, the intravital difference in the size of the pupils is preserved both on the corpse and with postmortem constriction of the pupils.

In fact, the substrate of the supravital pupillary reaction is the survival of the smooth muscles that form the sphincter of the pupil and the dilator of the pupil, and their retention of the ability to both perceive chemical irritants and react accordingly, dilating or constricting the pupil, i.e., to perform the functions inherent in a living person. This reaction is akin to other supravital reactions, in particular supravital tissue staining based on the retention of the permeability of cell membranes with respect to vital dyes. An example is the eosin test, when selective exclusion of eosin by the membranes of "living" cells and free penetration into "dead" cells is noted, i.e., their staining. The marker of survival of the smooth muscles of the sphincter of the pupil and the dilator of the pupil is their response to chemical irritants - the pupillary reaction.

Only local irritants have an effect, in particular chemicals that act directly on smooth muscle cells. Such chemicals include pharmacological drugs used in ophthalmological practice.

To dilate the pupil in ophthalmology, pharmacological drugs called miotics are used. They include two subclasses of drugs - M-cholinomimetics and anticholinesterase drugs. Anticholinesterase drugs have pronounced side effects of both local and systemic nature, and therefore are practically not used. The pharmacodynamics of M-cholinomimetics consists in stimulating M-cholinoreceptors of the smooth muscles of the iris, resulting in contraction of the sphincter muscle and the development of miosis. M-cholinomimetics are pilocarpine, carbachol and aceclidine.

To dilate the pupil and obtain mydriasis, pharmacological drugs called mydriatics are used. This pharmacotherapeutic group - mydriatic and cycloplegic agents - includes drugs that have a similar pharmacological effect, but have different chemical structures and pharmacodynamics, which determine the implementation of the final effect. This group includes cycloplegic mydriatics (M-anticholinergics) and non-cycloplegic mydriatics (sympathomimetics). The pharmacodynamics of M-anticholinergics is due to the blockade of M-cholinergic receptors, which are located in the sphincter muscle of the pupil, resulting in passive dilation of the pupil due to the predominance of the tone of the dilator muscle and relaxation of the sphincter muscle. M-anticholinergics are distinguished by the strength and duration of action: short-acting - tropicamide; long-acting - atropine, cyclopentolate, scopolamine, homatropine. The pharmacodynamics of sympathomimetics that have a mydriatic effect is due to their agonism to alpha-adrenoreceptors, stimulating and increasing their functional activity, which leads to an increase in the tone of the dilator muscle, as a result of which the pupil dilates (mydriasis develops). Sympathomimetics include phenylephrine, mesaton, and irifrin.

The range of pharmacological preparations used to assess the supravital pupillary reaction in the works of K. I. Khizhnyakova and A. P. Belov was limited to atropine and pilocarpine. The dynamics of the supravital reaction was established only for pilocarpine; the influence of environmental factors and causes of death was not taken into account. Further study of the reaction of the smooth muscles of the iris to chemical irritants, namely, to modern pharmacological preparations used in ophthalmological practice, seems promising.

D. B. Gladkikh. Supravital pupillary reaction// International Medical Journal - No. 3 - 2012

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