The corneal reflex (or in other words corneal, blinking, conjunctival) is a natural reaction of the body to irritation of the cornea of the eyes. Checking its absence or weakening serves as an auxiliary diagnostic sign of some pathologies. The corneal reflex also allows you to assess the degree of immersion in anesthesia.
General Description
The cornea of the eye of humans and other animals is highly sensitive. This is due to the fact that around it there is a nerve plexus of long ciliary nerves. They do not have a myelin sheath in the cornea and therefore become invisible.
There are 3 levels of nerve entanglements. The closer the nerves are located to the corneal surface, the thinner and thicker they are. A separate nerve ending is present in almost every cell of the outer layer of the cornea. Therefore, a person experiences a pronounced pain syndrome with mechanical irritation of this area, as well as with its inflammatory diseases.
High sensitivity of the cornea is one of the natural protective mechanisms of the organs of vision. The corneal corneal reflex is especially pronounced innewborn babies. After 1 year of life, it gradually weakens. In adults, in isolated cases, it may not be detected at all.
How does it manifest itself?
The corneal reflex manifests itself as the following process:
- eyelids close;
- eyeball turns up, removing the cornea under the eyelids;
- tear glands secrete a fluid that washes away irritating particles.
The reflex can occur when the cornea is lightly touched or even when there is air movement, a sudden increase in light, an object rapidly approaching the eye, or a reaction to a sudden loud sound.
Views
The corneal reflex can be divided into 2 categories:
- corneal, caused by corneal irritation;
- conjunctival (conjunctival) - when exposed to the conjunctiva.
The latter is often absent in he althy people.
The sensitive part of the reflex arc is performed by the trigeminal nerve, and the motor part by the facial nerve.
Diseases
Loss or weakening of the corneal blinking reflex is observed under the following conditions:
- severe brain injury (in particular, in its stem part), accompanied by coma;
- damage to the cervical vertebrae;
- a tumor of the auditory nerve, while the patient also has unilateral hearing loss and swallowing problems;
- organic trigeminal lesion, facialnerve;
- pathological changes in the cornea itself;
- deformation of the pons, which is responsible for the transmission of impulses from the spinal cord to the brain.
The reflex can also fade with hysteria, especially on the side of the face where the loss of skin sensation occurs.
Conducting a study of the corneal reflex
The procedure for checking the reaction of the eye is performed in the following order:
- the patient is placed on the couch in a horizontal position;
- raise the upper eyelid to open the palpebral fissure;
- touch a piece of sterile cotton to the cornea.
If the eyeball “rolled up” and the eyelids closed, then the reflex is not disturbed, and vice versa. In patients who are unconscious, the study is carried out similarly. Sometimes for these patients, the test is done with a thin stream of water.
The intensity of the corneal reflex, as for other tests performed on mucous membranes, varies widely.
Influence of drugs and other substances
Reduction of this reflex occurs not only with traumatic brain injuries and diseases of the central nervous system, but also with the use of certain drugs. These include the following tools:
- sedative;
- barbituric acid derivatives;
- painkillers;
- antipsychotic;
- anticonvulsants;
- antiemetic;
- drugs for the treatment of Parkinson's disease.
Violation of the normal reaction of the cornea is also observed with the abuse of alcoholic beverages and with an overdose of narcotic substances.
Corneal reflex occurs in patients who use contact lenses for the eyes. The cornea perceives them as a foreign body, so there are unpleasant sensations. However, this does not mean that this effective method of vision correction will have to be abandoned. In order to get used to the lenses, doctors recommend “training” the eyes a few weeks before the start of their use by touching them with a piece of sterile cotton wool. Before doing this, wash your hands thoroughly so as not to infect.
Meaning in medical diagnostics
Inhibition of the corneal reflex may indicate that the patient has fallen into a coma. If the reflex weakened gradually, then this makes it possible to suspect the presence of an internal hemorrhage in the brain, in which the affected area increases in size over time. And vice versa, if the reflex suddenly appears again, then this indicates an improvement in the person's condition after a traumatic brain injury.
However, this symptom cannot serve as the only diagnostic criterion. It is auxiliary in a comprehensive examination of the patient.
The study of the corneal reflex helps not only to identify certain pathologies, but also serves to determine the degree of immersion of a person in general anesthesia before conductingsurgery.
After the injection of an anesthetic, the doctor always checks the reaction of the cornea of the eye. If it is absent, then this means that the drug has reached the brain stem, and the patient will not feel pain during surgical procedures.
