Study of pupillary reactions. Impaired pupillary reactions

Normally, the pupil of a person is
moderate diffuse illumination of the eye with
its directionality into the distance is 3 - 4.5 mm
- n/w pupil is less than 3 mm
- 10 years pupil width 4 – 4.5 mm
- 40 – 50 years is equal to 3 – 4 mm
- after 60 years it decreases to 1 – 2 mm

The width of the pupil depends on the state of the two
smooth muscles of the eye
- pupillary sphincter (parasympathetic)
- pupil dilator (sympathetic innervation)

Constriction of the pupil (miosis) may be
pathological if the diameter is less than 2 mm
Types of pathological miosis:
- Active (spastic) miosis caused by excitement
parasympathetic structures
oculomotor nerve
- Passive (paralytic) miosis –
a consequence of suppression of the sympathetic
innervation of the muscle that dilates the pupil (
with Claude–Bernard–Horner syndrome)

Mydriasis can be pathological if
its d > 4 – 4.5 mm
Types of mydriasis
- active (spastic) – with
muscle contraction that dilates the pupil
due to irritation of the sympathetic
structures
- passive (paralytic) – violation
functions of parasympathetic structures
oculomotor nerve and as a consequence
pupillary sphincter paralysis

Anisocoria – difference in pupil size
(it is possible normally in almost 30%
healthy people). Anisocoria may be
pathological if the difference in width
pupils exceeds 0.9 mm.

The light reflex is a complex four-neuron arc:
1st neuron: from retinal photoreceptors to pretectal nuclei
in the midbrain;
2nd neuron: from each pretectal nucleus to both nuclei
Yakubovich - Edinger - Westphal.
3rd neuron: from the above nuclei it goes into the thickness of the third pair
cranial nerves to the ciliary ganglion in the orbit. It is important to know,
that these fibers exit the third pair from the midbrain
are located superficially, so they can be compressed
aneurysm of the internal carotid artery, however, passing through
lateral wall of the cavernous sinus, they are located
more centrally, and therefore even with full external
Ophthalmoplegia is usually not affected; pupillary in the eye socket
autonomic fibers from the inferior branch of the oculomotor
nerves branch off to form the oculomotor (parasympathetic)
a root whose fibers are directed to the ciliary ganglion.
4th neuron: from the ciliary ganglion (which, although containing a number
other fibers, only for parasympathetic is
synapse) pupillary fibers together with short
ciliary nerves reach the sphincter of the pupil.

Pattern of pupillary reflexes: direct and friendly reactions to light.

Pupil response to accommodation and convergence

When examining an object up close
distance with one eye reflexively
accommodation of the lens occurs, which
accompanied by constriction of the pupil, which contributes to
improving vision clarity.
When the patient looks at the approaching
bridge of the nose subject with two eyes, along with
accommodation of the lenses is accomplished
convergence of the eyes, the bringing together of their visual
axes that provide focusing
reflection of an object on the macular area
retinas of both eyes. At the same time there arises
constriction of both pupils.

Pupil response to eyelid closure

Constriction of the pupil when the eyelids close I.I.
Merkulov (1962) explained by the presence of a straight line
connections in the brainstem between the nuclei of the facial and
oculomotor nerves.
Reflex arc from circular receptors
muscles of the eye along the facial nerve reaches
its nuclei, closes in the brain stem between
this nucleus and the nuclei of the oculomotor
nerve, after which its efferent part
passes along the oculomotor nerve and beyond
through the ciliary ganglion to the pupillary sphincter.

Trigemino-pupillary reflex

This is a constriction of the pupil, which can
precede short-term and
its slight expansion in response to
tactile or painful stimulation
cornea, conjunctiva, eyelid skin or
periorbital region.
A variant of this reflex is
Raeder's syndrome - constriction of the pupils and
palpebral fissures during hypertensive
crisis or migraine attack.

Galvano-pupillomotor reaction of the pupils

Constriction of the pupils under the influence of weak
galvanic current passing through
eyeball. Current 1.5 – 3 mA

Pupil dilation reaction to pain

Reflex pupil dilation
the influence of pain is known as a reflex
Piltz – 1.
Reason: emotional stress
(catecholamine release ---- total
sympathoadrenal reaction --- tension of the muscle that dilates the pupil)

Reaction of the pupils upon stimulation of the vestibular apparatus

The vestibular-pupillary phenomenon
reflex is characterized by narrowing
pupils alternating with their dilation to
1 -2 sec. Is a consequence of braking
parasympathetic nuclei
oculomotor nerve or the result
excitation of sympathetic structures,
involved in the innervation of the eye.

Breathing pupillary reflexes

Dilation of the pupil when taking a deep breath and
narrowing when exhaling
The reflex is unstable and conditioned
changes in parasympathetic reactions
internal muscles of the eye,
provoked by changes in
deep breathing movements
functional state of the vagus
nerves.

Dilated pupils under the influence of psychogenic stress

The Rigel reflex is directly proportional
severity of the stressful situation
The pupils can reach up to 8 – 9 mm, which
provoked by activation of cortical
structures through the limbic - reticular
complex

Reactions of pupils to pharmacological agents

In case of poisoning with drugs from the group
tranquilizers, miosis is observed with
preserved reaction of the pupils to light, and
also in patients in a state of coma 1 – 2
degrees.
In case of poisoning with opium and
medicines from the group
antipsychotics are observed
pupils that respond sluggishly or not
responsive to light.

The eyes are a fairly important organ for the normal functioning of the body and a full life. The main function is the perception of light stimuli, which is why the picture appears.

Structural features

This peripheral one is located in a special cavity of the skull called the orbit. The eye is surrounded on the sides by muscles with which it is held and moved. The eye consists of several parts:

1. Directly the eyeball, which has the shape of a ball measuring about 24 mm. It consists of the lens and aqueous humor. All this is surrounded by three membranes: protein, vascular and reticular, arranged in reverse order. The elements that make up the picture are located on the mesh shell. These elements are receptors that are sensitive to light;
2. The protective apparatus, which consists of the upper and lower eyelids, the orbit;
3. Adnexal apparatus. The main components are the lacrimal gland and its ducts;
4. The oculomotor system, which is responsible for the movements of the eyeball and consists of muscles;

Main functions

The main function that vision performs is to distinguish between various physical characteristics of objects, such as brightness, color, shape, size. In combination with the action of other analyzers (hearing, smell and others), it allows you to regulate the position of the body in space, as well as determine the distance to an object. That is why prevention of eye diseases must be carried out with enviable regularity.

Presence of pupillary reflex

At normal functioning organs of vision, with certain external reactions, so-called pupillary reflexes arise, in which the pupil narrows or dilates. The pupil of which is the anatomical substrate of the pupil's reaction to light, indicates the health of the eyes and the whole organism as a whole. That is why, in some diseases, the doctor first checks for the presence of this reflex.

What is the reaction?

The reaction of the pupil or the so-called pupillary reflex (other names are iris reflex, iritic reflex) is some change linear dimensions pupil of the eye. Constriction is usually caused by contraction of the muscles of the iris, and the reverse process - relaxation - leads to dilation of the pupil.

Possible reasons

This reflex is caused by a combination of certain stimuli, the main one of which is considered to be a change in the level of illumination of the surrounding space. In addition, changes in pupil size can occur for the following reasons:

• the effect of a number of medications. That is why they are used as a way to diagnose drug overdose or excessive depth of anesthesia;
• changing a person's point of focus;
• emotional outbursts, both negative and positive in equal measure.

If there is no reaction

Lack of pupillary response to light may indicate various states people who pose a danger to life and require immediate intervention from specialists.

Diagram of the pupillary reflex

The muscles that control the functioning of the pupil can easily influence its size if they receive a certain stimulus from the outside. This allows you to regulate the flow of light that enters directly into the eye. If the eye is covered from incoming sunlight and then opened, the pupil, which previously expanded in the dark, immediately decreases in size when light appears. The pupillary arc of which begins on the retina indicates the normal functioning of the organ.

The iris has two types of muscles. One group appears to be rings muscle fibers. They are innervated by parasympathetic fibers of the optic nerve. If these muscles contract, then this process causes Another group to dilate the pupil. It includes radial muscle fibers that are innervated by sympathetic nerves.

The pupillary reflex, the pattern of which is quite typical, occurs in the following order. Light that passes through and is refracted through the layers of the eye hits the retina directly. The photoreceptors that are located here are in in this case are the beginning of the reflex. In other words, this is where the path of the pupillary reflex begins. The innervation of the parasympathetic nerves affects the functioning of the sphincter of the eye, and the arc of the pupillary reflex contains it in its composition. The process itself is called the efferent arm. The so-called center of the pupillary reflex is located right there, after which various nerves change their direction: some of them go through the cerebral peduncles and enter the orbit through the upper fissure, others - to the sphincter of the pupil. This is where the path ends. That is, the pupillary reflex closes. The absence of such a reaction may indicate some kind of disorder in the human body, which is why such great importance is attached to this.

Pupillary reflex and signs of its damage

When examining this reflex, several characteristics of the reaction itself are taken into account:

• the amount of pupil constriction;
• form;
• uniformity of reaction;
• pupil mobility.

There are several most popular pathologies indicating that the pupillary and accommodative reflexes are impaired, which indicates problems in the body:

• Amaurotic immobility of the pupils. This phenomenon represents the loss of a direct reaction when illuminating a blind eye and a friendly reaction if there are no problems with vision. The causes are most often a variety of diseases of the retina itself and the visual pathway. If the immobility is one-sided, is a consequence of amaurosis (damage to the retina) and is combined with pupil dilation, albeit slight, then there is a possibility of developing anisocoria (the pupils become different sizes). With this disorder, other pupillary reactions are not affected in any way. If amaurosis develops on both sides (that is, both eyes are affected at the same time), then the pupils do not react in any way and even when exposed to sunlight remain dilated, that is, the pupillary reflex is completely absent.
• Another type of amaurotic pupillary immobility is hemianopic pupillary immobility. Perhaps there is damage to the optic tract itself, which is accompanied by hemianopsia, that is, blindness of half of the visual field, which is expressed by the absence of the pupillary reflex in both eyes.

• Reflex immobility or Robertson's syndrome. It consists in the complete absence of both direct and friendly reactions of the pupils. However, unlike the previous type of lesion, the reaction to convergence (constriction of the pupils if the gaze is focused on a certain point) and accommodation (change external conditions, in which a person is located) is not violated. This symptom is due to the fact that changes occur in the parasympathetic innervation of the eye when there is damage to the parasympathetic nucleus and its fibers. This syndrome may indicate the presence of a severe stage of syphilis nervous system, less often the syndrome reports encephalitis, a brain tumor (namely in the region of the legs), as well as traumatic brain injury.

The causes may be inflammatory processes in the nucleus, root or trunk of the nerve responsible for eye movements, a lesion in the ciliary body, tumors, abscesses of the posterior ciliary nerves.

Clinical death can develop for a number of reasons. For example, in case of electric shock, suffocation, poisoning, a number of dangerous pathologies etc.

It is very important for doctors to know the signs that can distinguish loss of consciousness from death.

If resuscitation is performed correctly, a person can be quickly brought out of clinical death.

Important! One of the signs of this condition is the lack of reaction from the pupils. They remain dilated and do not respond to external stimuli.

Structure

Many people believe that the hole in the central part of the iris is the pupil. In fact, its constitution is much more complex. It consists of muscle tissue, which is necessary to ensure the necessary supply of light penetrating the iris area.

These muscles are called:

• sphincter,
• dilator.

Sphincter muscle located around the hole and is responsible for the constriction of the pupil.

The basis of the sphincter is made up of fibers. The thickness of the sphincter is a constant value that ranges from 0.07-0.17 mm. The width of the layer ranges from 0.6 to 1.2 mm.

Dilator serves to dilate the pupil. It consists of spindle-shaped epithelial tissue with an inner core. The dilator has two muscle layers - anterior and posterior, which are closely intertwined with the iris and pupillary opening.

For diseases of the pupillary reflex, the following diagnostics are carried out:

1. External examination, which reveals the size and asymmetry of the pupils of both eyes.
2. The direct and cooperative reaction of the pupils to light radiation is assessed.
3. Testing for components such as convergence and accommodation.

How the human eye works is explained in the video:

Reaction to light

Research, which reveal the reaction of the pupil to the flow of light:

1. Direct reaction.
2. A reaction that is called friendly.
3. Convergence and accommodation.

Direct response is checked like this:

1. The person is seated facing the light source.
2. One eye is covered with a hand, the other is peering into the distance.
3. The eyes are alternately closed and opened, while the doctor observes the reaction of the pupil.
4. If there are no deviations, then the pupil narrows in the dark, and becomes wider in bright light.

When a diagnosis is made using friendly response, one eye is alternately darkened and then illuminated. The ophthalmologist monitors the reaction of the pupil of the second eye. Normally, it should also expand in the presence of light and contract in its absence.

And another method - a reaction to convergence and accommodation - involves tracking objects. If any object is close to the eyes, the pupils narrow. The further away the object of observation, the wider the pupils will become.

Reference! Sometimes the doctor uses his index finger. The patient looks at its tip, which either approaches or moves away.

Sometimes there is a disturbance in the reactions of the eye pupil, for example:

• due to pathologies of the optic nerve;
• the nerve responsible for eye movement;
• with Eddie's syndrome.

In addition to the reaction of the pupil to light, its diameters can be changed in the following cases:

1. With convergence, when the tone of the internal muscles of the eye increases when the pupils are brought to the nose.
2. During accommodation, the tone of the ciliary muscle changes when the gaze moves from the near to the far distance.

Dilation of the pupil area can also be observed in the following situations:

1. In case of fear, most likely for this reason the expression “fear has big eyes” arose.
2. For pain.
3. During times of strong emotions or nervous excitement.

The pupil's volume may change with the use of certain medicines, which affect the proprioceptors of the eye muscles.

Appearance when brain cells die

Clinical death is a process when blood circulation in the body stops, breathing stops and a pulse cannot be heard. But at the same time, all these processes are reversible, since there are no necrotic changes in the central nervous system and other organs of the human system.

Clinical death can last from 3 to 6 minutes; until this time, parts of the brain do not lose their viability to a state of hypoxia. Required in as soon as possible carry out resuscitation, only in this case does the person have a chance to live.

Important! In clinical death, the light reaction of the pupils is preserved. But the person lacks all signs of life.

These circumstances are the highest reflex, closing in the cerebral cortex in the brain. From this we can conclude that as long as these large hemispheres are functioning, the pupil will not lose its ability to respond to light.

When biological death occurs, the pupils are also dilated in the first moments. This is due to the convulsive and agony state of the body.

During clinical death, the openings of the pupils, regardless of the lighting, will be dilated. The skin turns pale, takes on a lifeless hue, the muscles relax, and there are no signs of even slight tone.

Dilated pupils and non-response to lighting are a sign of brain hypoxia. This condition develops at 40-60 seconds of circulatory arrest and the onset of clinical death.

Other signs

In addition to the fact that the pupils are dilated at the moment of clinical death, there are also other distinctive features states:

1. There is no pulse, and only by the carotid or femoral artery can one determine that the person is alive. To do this, the ear is applied to the heart, where the heartbeat is heard.
2. Blood circulation stops.
3. The person completely loses consciousness.
4. No reflexes.
5. The breathing is extremely weak and can be seen upon close inspection during inhalation or exhalation.
6. Blue and pale skin.
7. The pupils are dilated, there is no reaction to light.

Reference! When biological death occurs, the shape of the pupil will be called a “cat’s eye”, that is, during the next 60 minutes after death, when pressure is applied to the eyeball, the pupil takes the form of a narrow slit.

The video describes the signs of clinical death:

In order to provide maximum assistance to save a person who is in a state of clinical death, it is necessary, before the ambulance arrives, to do everything necessary to resuscitate him, perform artificial respiration and cardiac massage.

In children of the first year of life, the pupil is narrow (2 mm), reacts poorly to light, and dilates poorly. In the sighted eye, the size of the pupil constantly changes from 2 to 8 mm under the influence of changes in illumination. IN room conditions in moderate lighting, the pupil diameter is about 3 mm, and in young people the pupils are wider, and with age they become narrower.

Under the influence of the tone of the two muscles of the iris, the size of the pupil changes: the sphincter contracts the pupil (miosis), and the dilator ensures its dilation (mydriasis). Constant movements of the pupil - excursions - dose the flow of light into the eye.

The change in the diameter of the pupillary opening occurs reflexively:

• in response to irritation of the retina by light;
• when setting to clearly see an object at different distances (accommodation);
• with convergence (convergence) and divergence (divergence) of the visual axes;
• as a reaction to other irritations.

Reflex dilation of the pupil can occur in response to a sharp sound signal, irritation of the vestibular apparatus during rotation, with unpleasant sensations in the nasopharynx. Observations are described confirming the dilation of the pupil under great physical stress, even with a strong handshake, when pressing on individual areas in the neck, as well as in response to a painful stimulus in any part of the body. Maximum mydriasis (up to 7-9 mm) can be observed during painful shock, as well as during mental stress (fear, anger, orgasm). The reaction of pupil dilation or constriction can be developed as conditioned reflex the words dark or light.

Reflex from trigeminal nerve(trigeminopupillary reflex) explains the rapidly alternating dilation and contraction of the pupil when touching the conjunctiva, cornea, eyelid skin and periorbital region.

The reflex arc of the pupillary reaction to bright light is represented by four links. It starts from the photoreceptors of the retina (I), which received light stimulation. The signal is transmitted along the optic nerve and optic tract to the anterior colliculus of the brain (II). The efferent part of the arc of the pupillary reflex ends here. From here, the impulse to constrict the pupil will go through the ciliary node (III), located in the ciliary body of the eye, to the nerve endings of the sphincter of the pupil (IV). After 0.7-0.8 s, the pupil will contract. The entire reflex path takes about 1 s. The impulse to dilate the pupil comes from the spinal center through the superior cervical sympathetic ganglion to the pupillary dilator (see Fig. 3.4).

Drug dilation of the pupil occurs under the influence of drugs belonging to the mydriatic group (adrenaline, phenylephrine, atropine, etc.). The most persistent dilation of the pupil is a 1% atropine sulfate solution. After a single instillation in a healthy eye, mydriasis can persist for up to 1 week. Short-acting mydriatics (tropicamide, midriacil) dilate the pupil for 1-2 hours. Constriction of the pupil occurs when miotics are instilled (pilocarpine, carbachol, acetylcholine, etc.). U different people the severity of the reaction to miotics and mydriatics is not the same and depends on the ratio of the tone of the sympathetic and parasympathetic nervous systems, as well as the state of the muscular apparatus of the iris.

Changes in the reactions of the pupil and its shape can be caused by an eye disease (iridocyclitis, trauma, glaucoma), and also occurs with various lesions of the peripheral, intermediate and central parts of the innervation of the iris muscles, with injuries, tumors, vascular diseases brain, upper cervical ganglion, nerve trunks.

After a contusion of the eyeball, post-traumatic mydriasis may occur as a consequence of sphincter paralysis or dilator spasm. Pathological mydriasis develops in various diseases of the thoracic and abdominal organs (cardiopulmonary pathology, cholecystitis, appendicitis, etc.) due to irritation of the peripheral sympathetic pupillomotor pathway.

Paralysis and paresis of the peripheral parts of the sympathetic nervous system cause miosis in combination with narrowing of the palpebral fissure and enophthalmos (Horner's triad).

In hysteria, epilepsy, thyrotoxicosis, and sometimes in healthy people, “jumping pupils” are observed. The width of the pupils changes independently of the influence of any visible factors at uncertain intervals and inconsistently in the two eyes. In this case, other eye pathology may be absent.

Changes in pupillary reactions are one of the symptoms of many general somatic syndromes.

If the reaction of the pupils to light, accommodation and convergence is absent, then this is paralytic immobility of the pupil due to pathology of the parasympathetic nerves.

Methods for studying pupillary reactions are described in

So far we have been talking about arbitrary movements of the ocular apparatus. But along with them, there are also movements of the pupil, which are already involuntary; they proceed, as they say, as a reflex. In view of the great importance of these pupillary reactions for the clinic, I consider it necessary to consider their physiology and anatomical substrate separately.

Reflex movements of the pupil, i.e. contractions of the iris, occur:

1) from the action of light on the eye, 2) under the influence of accommodation and 3) under the influence of convergence of the eyeballs.

These three types of reflexes are therefore called: 1) reaction to light,

2) reaction to accommodation and 3) reaction to convergence.

All these three types of reactions consist of constriction of the pupil.

The light reaction of the pupil has the peculiarity that it occurs not only on the eye that is directly illuminated - direct reaction - but also on the opposite - friendly reaction. \

The anatomical substrate of the light reaction of the pupil, like any reflex in general, is a special reflex arc with adductor and abductor halves. Only the structure of this arc, compared to the arcs of spinal reflexes, is more complex.

Adducting half formed by the fibers of the optic nerve, or more precisely, by a part of them that makes up the so-called maculopupillary bundle, already known to you from the description of the II pair.

I said at one time that the fibers of the maculopupillary bundle end in the anterior colliculus. Now it is necessary to recall one important detail regarding this ending: approaching the anterior colliculus, these fibers end in terminal branches not only on their side, but also on the opposite side. They, therefore, make a partial crossover here too. This is where the adductor half of the reflex arc ends, and then the abductor part begins.

This outlet part formed by IIIdara fibers. The cells that give rise to these fibers constitute what is called the nucleus of Edinger-Westphal, and perhaps also the median nucleus of Perlia. The processes of these cells go among the fibers of the oculomotor nerve into the orbit, enter a special sympathetic ganglion - ganglionciliare - and end near its cells. The latter give rise to the next motor neuron, which, as part of the so-called n.ciliares, enters the m.sphincterpupillae and supplies it with its branches (Fig. 60).

From this description you can see that the motor half of the light reflex arc consists not of one neuron, but of two.

You remember that such a structural plan is characteristic of the sympathetic system and is completely unusual for the somatic nervous system, which has only one peripheral neuron.

You must therefore clearly and distinctly understand that in the nucleus of the oculomotor nerve, among the cells of a somatic nature, there are also cells of a sympathetic nature, this is precisely the nucleus of Edinger-Westphal and Perlia. The processes of these two types of cells run together to form what is known in gross anatomy as the oculomotor nerve. Therefore, the so-called n.oculomotorius there is an anatomical formation of mixed nature - half sympathetic, half somatic. And this applies equally to both the peripheral nerve and its core. How are the adductor and abducent halves of the arc of the pupillary reflex connected?

Rice. 60. Arc of the pupillary reflex.

Small dotted line - adductor half of the arch - maculopupillary. bunch; large dotted line - abducent half of the arc - the path to the sphinct pup; solid line - path to dilatator pupillae; 1C - 2C - 3C - three cervical sympathetic nodes.

This issue is not completely resolved. It is believed that the terminal branches of the maculopupillary tract directly come into contact with the sympathetic cells of the oculomotor nerve nucleus, just as, for example, the fibers of the dorsal roots come into contact with the peripheral motor neuron.

Others think that between the two halves of this reflex arc there is one extra interneuron that plays the role of a connecting link.

Therefore, the mechanism of the light reflex must be imagined this way.

Light stimulation falling on the macula runs through the maculopupillary fascicle and is transmitted to the sympathetic group of cells located in the nucleus of the oculomotor nerve, on its side and on the opposite side. The motor discharge of these cells runs through two peripheral neurons of the sympathetic nerve and causes a contraction of m. sphincterisiridis on its side (direct reaction) and on the opposite side (friendly reaction).

I called this process the “pupillary reflex” mechanism. We need to introduce more clarity into this terminology now. The one I described to you is a mechanism constriction of the pupil under the influence of light. But the pupil is also expanding in the dark, i.e. in the absence of light.

What is the mechanism of this last movement and what is its anatomical substrate?

The muscle that dilates the pupil (m.dilatatorpupillae) is also innervated by the sympathetic system. The cells that give rise to the corresponding prenodal fiber are located in the lateral horn at the border of the cervical and thoracic spinal cord - this is the so-called centrumciliospinale. The processes of these cells exit through the eighth cervical and first thoracic anterior roots, pass through the ramicommunicantes into the borderline trunk of the sympathetic nerve and rise up to the first cervical ganglion.

The prenodal neuron ends in this node, and the postnodal neuron begins from its cells. The latter then, through the plexus caroticus, enters the cranial cavity along with the carotid artery, joins the first branch of the trigeminal nerve, together with it goes to the eyeball and branches into the m.dilatatorpupillae.

These two peripheral neurons make up outlet half reflex arc.

adductor, unfortunately, it is not known for sure. One might think that there are several driving systems. One of them is formed by conductors of pain sensitivity - especially from the upper ends of the body.

How can we imagine the relationship between these two mechanisms - those that constrict the pupil and those that dilate it?

At present we cannot give an exact answer to this question; the most plausible would seem to be this.

M. dilatatorpupillae, tonically stronger, strives to keep the pupil dilated all the time.

M. sphincterpupillae, tonically weaker, strives to close the opening of the pupil, but cannot overcome the action of the muscle that dilates the pupil. As a result of this struggle, the pupil has a certain average width. But when light falls on the retina, this irritation causes a reflex contraction of the sphincter, so strong that the latter can already overcome the tone of the dilator. As a result, the pupil narrows and a “reaction to light” occurs. But as soon as the light irritation disappears, the ratio of forces of the pupillary muscles immediately comes into its own: the m.dilatator, as the stronger one, takes over, the pupil dilates.

In addition to the reaction to light, there is also a reaction to accommodation- constriction of the pupil when accommodating close distances.

Although this movement of the pupil is called a “reaction”, however same its reflex nature is doubtful. It is more likely that here we are dealing with the conjugal movement of the sphincter of the pupil: apparently this muscle is connected by associative connections and therefore acts synergistically with the ciliary muscle, which determines accommodation.

The same can be said regarding the reaction to convergence: with this movement, there is an associative connection not only between both m.rectiinterni, but also the sphincter of the pupil.

Despite this understanding of the nature of the last two types of pupillary movements, they are still called “reactions”. Due to the wide prevalence of this term, I will also use it in further presentation, despite its controversy.

To finish with the anatomical and physiological side of pupillary movements, we need to say two words about their central drives.

As you already know, all movements of the pupil are performed by the sympathetic system. On the other hand, you heard when describing the sympathetic system that in the latter, in all likelihood, there are central drives from the cerebral cortex - homologues of the pyramidal tract - as well as cortical centers.

We know very little about the central drives for the pupillary muscles. There are quite a lot of experimental studies regarding the existence of cortical centers.

Apparently there are several such centers - at least they were found in the frontal, parietal, and occipital lobes. Fragmentary clinical observations seem to indicate the existence in humans of a center of pupil movement, at least in one of the frontal gyri - the second or third.