Shells and also the corneal reflex. What is a corneal reflex and what does its absence mean? Causes of weakened or absent corneal response
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Orienting signs of death
- motionless body position,
- pale skin,
- lack of breathing,
- lack of pulse and heartbeat,
- lack of sensitivity to painful and olfactory stimuli, lack of pupillary response to light, lack of corneal reflex.
Reliable signs of death
- change in the shape of the pupil to an oval shape when the eyeball is compressed - the "cat's pupil" phenomenon (Beloglazov's sign) - 15-25 minutes after death
- signs of drying of the cornea and white of the eye (Larche's spots) - 1.5-2 hours after death
- drop in body temperature to 20 o C, in the rectum to 23 o C
- early cadaveric changes (cooling, cadaveric spots, rigor mortis, cadaveric desiccation, autolysis). Cadaveric spots appear after 1.5-3 hours (sometimes after 20-30 minutes). Rigor mortis appears after 2-4 hours, first in the masticatory muscles. After 1.5-3 days, rigor disappears (resolves), which is expressed in muscle relaxation.
- Development of late or transformation of cadaveric changes (rotting, mummification, fat wax, peat tanning).
According to the order of the Russian Ministry of Health, the following signs indicate brain death:
- Complete and persistent lack of consciousness (coma).
- Atony of all muscles.
- Lack of response to strong painful stimuli in the area of the trigeminal points and any other reflexes that close above the cervical spinal cord.
- Lack of pupil reaction to direct bright light. It should be known that no medications that dilate the pupils were used. The eyeballs are motionless.
- Absence of corneal reflexes*.
- Absence of oculocephalic reflexes*.
- Absence of oculovestibular reflexes.
- Absence of pharyngeal and tracheal reflexes.
- Lack of spontaneous breathing.
Corneal reflex usually persists until the coma becomes very deep.
*With lesions of the brain stem, the oculocephalic reflex is absent, i.e. “doll eyes” test negative : When turning, the eyeballs move simultaneously with the head as if they were frozen in place. This test is also negative in cases of poisoning with certain medications (for example, an overdose of phenytoin, tricyclic antidepressants, barbiturates, and sometimes muscle relaxants, diazepam). This phenomenon can lead to the misconception of organic damage to the brain stem. However, in case of intoxication pupils - normal sizes, And their reaction to light is preserved.
The “doll eyes” test will be positive , if the patient's eyeballs move in a friendly manner in the direction opposite to the direction of head rotation.
The corneal reflex is caused by gently touching the iris of the eye with a cotton swab, and the conjunctival reflex is caused in the area of the conjunctiva of the eyeball. In response to this, the eyelids close. The pharyngeal reflex is caused by touching the back wall of the pharynx with a spatula or spoon. In response to this, swallowing or vomiting movements occur. The palatal reflex, or reflex from the soft palate, is caused by touching the soft palate with a spatula or spoon. The response is the raising of the soft palate and uvula. Abdominal reflexes are caused by line irritations of the abdominal skin below the costal arches (upper abdominal reflex), at the level of the navel (middle abdominal), above the inguinal fold (lower abdominal) (Fig. 40). The response is expressed in the contraction of the abdominal muscles. The cremasteric, or scrotal, reflex is examined in boys. When the skin of the inner thigh is irritated, the testicle on this side is pulled upward. The anal reflex is caused by a prick of the skin near the anus. At the same time, its circular muscle contracts. The plantar reflex occurs when the skin on the outer edge of the sole is irritated from top to bottom. At the same time, the toes bend. In children under the age of 1.5 years, this reflex is of a different nature: in response to line irritation of the sole, the fingers do not bend, but fan-shaped spreading and straightening them - the Babinsky phenomenon. In older children and adults, the Babinski phenomenon is observed when the pyramidal system is damaged (separation of the peripheral motor neuron from the cerebral cortex).
DEEP REFLEXES. The brow reflex is caused by hitting the edge of the brow ridge with a hammer. The response is the closing of the eyelids. The mandibular reflex occurs when hitting the chin with a hammer with the mouth slightly open; in response to this, the lower jaw rises. The reflex from the biceps tendon is caused by hitting the biceps tendon with a hammer while the forearm is bent at the elbow joint. In this case, the forearm flexes at the elbow joint. The reflex from the triceps tendon, or extensor-ulnar, is caused by hitting the triceps tendon with a hammer; the arm should be bent at the elbow joint at a right angle. In response to irritation, the forearm extends. The metacarpal radial reflex is caused by a hammer blow on the styloid process of the radius. In response to this, flexion at the elbow joint, inward rotation of the forearm and flexion of the fingers occur. The inward rotation of the forearm is most pronounced; other reactions are inconsistent. The scapulohumeral reflex is caused by hitting the inner edge of the scapula with a hammer: adduction and outward rotation of the shoulder are noted. Deep abdominal reflexes are caused by hitting the pubis with a hammer 1 - 1.5 cm to the right and left of the midline (pubic abdominal reflex). In response to irritation, the abdominal wall on the corresponding side contracts. The costo-abdominal reflex is caused by a hammer blow on the edge of the costal arch slightly inward from the nipple line. In response to this, the abdominal muscles contract. The knee reflex is caused by hitting the quadriceps tendon below the kneecap with a hammer. In this case, the leg is extended at the knee joint. The Achilles reflex is induced by hitting the Achilles tendon with a hammer. In this case, plantar flexion of the foot is observed
Corneal reflex (corneal reflex) is an unconditioned reflex of closing the palpebral fissure in response to irritation of the cornea of the eye. A weakened or absent reflex may be associated with organic damage to the trigeminal or facial nerve, the brainstem, as well as pathological processes in the cornea itself.
The corneal or corneal reflex is one of the unconditioned reflexes.
It is triggered when the cornea of the eye is touched, manifested by the closure of the palpebral fissure. The cornea is equipped with a special layer of sensory cells connected to the nerve fibers of the trigeminal and facial nerves. The reflex is designed to ensure the safety of the cornea in case of risk of mechanical or other damage.
The absence of a corneal reflex may indicate decreased sensitivity of the cornea or diseases of the trigeminal or facial nerves. Also, the reflex is absent in a state of deep coma.
Anesthesiologists check for the preservation of the corneal reflex: when immersed in deep anesthesia, the reflex should disappear completely.
The motor reaction consists of the same closing of the eyelids; the reflex arc is the same as that of the brow reflex: r. ophthalmicus (I branch of the trigeminal nerve), sensory nucleus n. trigemini, motor nucleus n. facialis, n. facialis.
To induce the corneal reflex, the doctor asks the patient to look up and slightly to the side. At this moment, from the lower outer side of the eye, with a strip of soft paper 2-3 mm wide, without touching the eyelashes, he touches the cornea above the iris (not above the pupil - website note). The response is the closing of the eyelids. The reflex is always evoked in healthy people. It disappears when the trigeminal or facial nerves are affected.
Unilateral paralysis of the motor portion of the trigeminal nerve causes difficulty chewing on the affected side.
The tension of the temporal and masticatory muscles on this side is weakened. These muscles turn out to be thinner. When opening the mouth, the lower jaw deviates to the painful side (predominance of the tone of the pterygoid muscles of the healthy side). The mandibular reflex is not evoked. The described movement disorders can be combined with anesthesia in the area of the mandibular branch. Sometimes the taste on the front 2/3 of the tongue is upset. In rare cases, central paralysis of the masticatory muscles is possible as part of pseudobulbar syndrome. The paralysis is bilateral, the mandibular reflex increases, and there is no amyotrophy.
The study of sensitivity in the trigeminal nerve area is carried out according to general rules. Pain and temperature sensitivity should be experienced not only in the direction from top to bottom (along the projection zones of the three branches), but also from the ear to the lips (along the zones of segmental innervation).
When the sensitive root of the trigeminal nerve is damaged, anesthesia covers the same half of the face and the scalp, all types of sensitivity are affected. In some cases, the maxillary or orbital branch may be involved in isolation, then sensitivity disorders occur in the area of their branching. When these branches are damaged, anesthesia of the cornea may occur and the corneal (corneal) reflex may disappear.
Pathological processes in the brain stem can involve different levels of the nucleus of the descending spinal tract of the trigeminal nerve. Anesthesia on the face in this case has a dissociated nature and is distributed not according to the projection of the branches of the trigeminal nerve, but according to the segmental type. When the caudal part of the nucleus is affected, the anesthesia zone covers the outer parts of the face, and when the oral part is affected, its central parts around the mouth and nose.
The trigeminal nerve is sometimes irritated, resulting in intense paroxysmal pain in the face - trigeminal neuralgia. According to their localization, pain usually coincides with the projection of one of the three branches of the nerve. In the intervals between attacks, the pain is absent or has a dull, aching character. The places where the branches of the trigeminal nerve enter the bony openings on the face (supraorbital, infraorbital, chin) can be painful when pressed (Balle’s pain points). True, this more often happens with neuritis, and not with neuralgia. With trigeminal neuralgia, so-called trigger, or trigger, zones are found on the skin of the face and on the mucous membrane of the mouth - areas the size of a small coin, touching which leads to a painful attack.
When the trigeminal nerve is irritated, a tonic spasm of the masticatory muscles - trismus - can develop. The teeth become clenched and the patient cannot unclench them. Most often, this phenomenon occurs with tetanus, occasionally with meningitis and other diseases.
Corneal reflex- a natural reflex that manifests itself by quickly closing the eyelids as a reaction to a mechanical effect on the cornea. If there is no reaction, then it is worth thinking about possible damage to the trigeminal or facial nerve, the brain in the stem part, or the presence of pathological processes in the cornea. This reflex is needed to protect the eyeball. Therefore, the cornea is equipped with a large number of sensitive cells that react instantly.
Inspection
It will not be difficult for an experienced specialist to check the corneal reflex. But even he must be extremely careful, because the eye is a very important and delicate organ in the human body. In order to carry out the manipulation, certain actions are performed:
PThe patient should lie down on the couch.
DThe actor lifts one eyelid to the person who has addressed him.
WITHThe specialist applies lightly moistened cotton wool to the cornea and identifies the presence of a reaction and its intensity.
If the corneal reflex is evoked, then the eyeball should roll back, as during normal sleep. The condition of the facial and trigeminal nerves is determined by the presence or absence of a reaction.
In the absence of a corneal reflex, the doctor can establish the fact that the patient he is examining is in a state of deep coma. For anesthesiologists, this reaction helps determine the depth of anesthesia. The corneal reflex is absent in patients under deep general anesthesia.
Causes of weakened corneal reflex
The absence of any reaction or the presence of a weak one can tell a lot, however, only at the level of suspicion. It may indicate the presence of many diseases; a diagnosis can only be made after a thorough examination. If a doctor has conducted a test and found that the reflex is impaired, then the following diseases and conditions can be suspected:
1. Deformation of the pons. This is one of the areas of the brain that is referred to as the hindbrain. It is he who is appointed to transmit information from the spinal cord to the brain and control the facial and trigeminal nerves.
2. Acoustic neuroma. A benign formation accompanied by hearing loss, pain and impaired swallowing function.
3. Also, the corneal reflex is inhibited when taking a large number of drugs with a sedative effect. These include antidepressants, barbiturates, antipsychotics and benzodiazepines. Analgesics can also affect the reflex.
4. Traumatic brain injuries can provoke both depression and, conversely, revival of the reflex. If revival may indicate an imminent exit from a coma, then depression signals a deterioration of the situation.
The presence or absence of a reflex greatly helps doctors assess the patient’s condition, especially if he is unconscious. The corneal reflex is distinguished by its constancy, and therefore is quite informative.
CNS depression - inhibition of the corneal reflex
In addition to a number of diseases and injuries, some drugs taken by a person can also suppress the reflex. This effect manifests itself after the cessation of reflexive eye movement and the lack of reaction of the pupils to the light stimulus. The following medications should be taken with extreme caution:
- antiemetics;
- emetics;
- sleeping pills;
- psychotropic;
- drugs intended to treat Parkinson's disease;
- analgesics;
- anticonvulsants.
TBI and corneal reflex
In the presence of a severe head injury, one of the first tests performed on the patient is. How to conduct hisperson in shock, unconsciousness or coma? Corneairritate with a delicate stream of water. Literally one drop of liquid is enough to understand how the victim’s cornea reacts.
In cases where the reflex decreases gradually, we can talk about the presence of an intracranial hematoma, which increases in size.
Anesthesia
The corneal reflex is also widely used by anesthesiologists in their work. When there is no reflex when the cornea is irritated, this means that the action of the anesthetic has reached its target, namely the brain stem. Now the body is “switched off” from the sensation of pain, which makes it possible to proceed with long and “shock” operations, even on vital organs.
If you touch the cornea with your finger, a healthy person will react to this by quickly closing the eyelids. This reaction is a reflexive protective mechanism that prevents mechanical damage to the eyes, and is called the corneal reflex. In this article, we will explain its functions and importance in detail.
What is the corneal (corneal) reflex?
The corneal reflex is a natural reaction of the cornea to mechanical irritation and is manifested by an instantaneous, short-term closure of the eyelids.
The delicate tissues of the eyeball are vulnerable to any external influences. Therefore, nature has equipped the cornea with a large number of nerve cells that instantly respond to any stimuli. The reflex narrowing of the palpebral fissure when a foreign object enters helps protect the organs of vision from damage and injury.
The presence of a normal corneal reflex often indicates that a person does not have neurological problems. If the reflex mechanism does not work, this can mean serious disturbances in the functioning of the brain and nervous system.
Therefore, doctors often need to study the corneal reflex. It is carried out as follows.
The patient is placed in a horizontal position (for example, on a hospital couch). Then the doctor carefully lifts the upper eyelid and touches the cornea with a piece of cotton wool. Normally, the eyeball should “roll” upward. If this does not happen, then the reflex is impaired. A similar test can be performed on those patients who are unconscious.
The importance of the corneal reflex for the diagnosis of neurological disorders
If a doctor's examination of the corneal reflex shows that there is no response to an external stimulus, this may mean a deep coma. In addition to coma, the absence or weakness of the corneal reflex may indicate a number of pathological conditions.
- Deformation of one of the areas of the brain, which is called the Varoliev bridge.
This part of the brain is responsible for transmitting information from the spinal cord to the brain, and also controls the facial and largest cranial nerves. This pathology may be indicated by an absent corneal reflex in combination with disturbances in the functioning of the extraocular muscles.
- Neuroma (benign tumor) of the auditory nerve.
This pathology is characterized by hearing loss on one side, impaired swallowing function, and pain. With a neuroma, the corneal reflex weakens.
- Head and brain injuries.
They can cause both a weakening and a revival of the reflex reaction of the cornea. The option of reflex inhibition is considered dangerous for the patient, which may indicate falling into a coma. If the reflex weakens gradually, the doctor may suspect the presence of an internal hematoma, which is gradually increasing in size. In the case when the reflex, on the contrary, suddenly appears, this may indicate an improvement in the patient’s condition after a traumatic brain injury. They check the reaction of the cornea in an unconscious person using a thin stream of water.
It is worth noting that the corneal reflex or its absence is not a clear reason for making a diagnosis. A diagnostic study of the corneal reaction is auxiliary in a comprehensive examination of the patient.
How is the corneal reflex related to the use of medications?
In addition to diseases, traumatic brain injuries, neurological disorders and other pathologies, the absence of the corneal reflex can be caused by external factors. In particular, the use of sedatives in large quantities leads to depression of the central nervous system, cessation of reflex movements of the eyeballs, lack of reaction of the pupils to light and weakening of the corneal reflex. Barbiturates, antipsychotics, anti-depressive medications, benzodiazepines, medications for Parkinson's disease, some analgesics, anticonvulsants, and anti-vomiting medications may have similar effects. They can partially “drown out” or lead to the complete disappearance of the corneal reflex. Alcoholic drinks in large volumes have a similar effect, so in people who abuse alcohol, the reaction of the cornea to external stimuli may be impaired.
How is the corneal reflex used to check the patient's readiness for surgery?
Sometimes the absence of a corneal reflex does not indicate a health problem, but is only a consequence of the fact that the person is under general anesthesia. In particular, anesthesiologists actively use this reflex mechanism in their professional activities. After administering the anesthetic, they always check the patient's corneal response to assess the depth of general anesthesia. When the reflex is completely absent, this means that the drug has reached the brain stem and now the patient will not be able to feel pain at all. In this state, even the most complex operations that last several hours can be performed.
Corneal reflex when wearing contact lenses
Today, many people have vision problems and are forced to use contact correction devices. Lenses are becoming more and more popular every year - they can be used in everyday life and during active training, they are invisible from the outside and do not affect appearance. In addition, the lenses qualitatively improve vision and maintain a wide peripheral view. It is natural that with so many advantages, the number of users of contact optics is only growing.
However, it should be understood that the lenses come into contact with the cornea and should cause a reflexive reaction of closing the eyelids.
Can the corneal reflex interfere with wearing contact lenses? Ophthalmologists explain that the cornea perceives lenses as a foreign object, and therefore reacts to them with an appropriate reflex. But this does not mean that you will have to give up the idea of wearing contact lenses forever. You just need to be prepared to wear them in advance. The essence of the training is to form a habit of touch.
To do this, a few days or weeks before using contact optics for the first time, start touching the sclera of your eye with your finger. Do this exercise only with clean hands, without making sudden movements. The first time, most likely, your corneal reflex will work, and your eyelids will close when touched. But if you repeat such manipulations every day, then after a few days the eyes will stop reacting in this way, the corneal reflex will disappear or become less pronounced. After this, you can safely use contact lenses without experiencing any difficulty in putting on or taking off.
The corneal reflex does not depend on the type of contact optics. This is a physiological reaction to any touch to the cornea. Therefore, it makes no difference what kind of lenses you plan to wear - for example, hydrogel Acuvue 1-Day Moist or silicone hydrogel Acuvue Oasys. In both cases, your eyes will easily get used to optical products if you spend a few days training to weaken the corneal reflex.
Summarizing
The corneal reflex is a physiological reaction of the eye to mechanical stimuli. Its absence or weakening may indicate neurological pathologies, head injuries, coma, or the use of certain medications. Using the corneal reflex, the anesthesiologist can determine how deeply the patient has gone into general anesthesia. When wearing contact lenses, the reflex reaction of the cornea can interfere only in the first stage. Special gymnastics will help speed up the eyes' adaptation to the lenses and weaken the corneal reflex.
