Corneal reflex

The blink reflex (also orbicularis oculi - reflex, corneal reflex, blink reflex ) is a reflex protective mechanism of the eye. It is triggered by mechanical effects on the cornea and the surrounding areas around the eyes and manifests itself by a rapid closure of the eyelids. It provides protection against foreign bodies from dehydration and against deterioration of the eyeball. An involuntary eyelid closure occurs even in strong light irritation to the eye on, impromptu acoustic stimuli, and as a result to a startle.

Neurophysiology

The blink reflex is a so-called foreign reflex. The afferent ( to the brain running ) limb of the reflex arc runs ( bright light ) via the optic nerve when tactile stimuli on the ophthalmic nerve, a branch of the fifth cranial nerve ( trigeminal nerve ), with visual stimuli. He directs the excitation by switching in Trigeminuskomplex via the superior colliculus and red nucleus to the reticular formation, only from there to the reflex center in the brain stem, the Fazialiskern. A small proportion of afferents reached this core directly. From there, via the efferent limb, the facial nerve ( cranial nerve VII), caused a contraction of the orbicularis oculi muscle. The reflex occurs within about 250 ms, however, react between 10% and 20 % of all subjects not with a blink reflex to light stimuli. Newborn (up to the age of about 1 ½ years ) may also point to acoustic stimuli a reflex lid closure.

As the pupillary reflex is the blink reflex a consensual reflex, that is, the afferents are routed to both premotor areas. Even when not irritated eye, the eyelid closes ( the pupillary reflex narrows in unilateral irradiation the other eye ).

Lidschlussreflexzeit

The Federal Institute for Occupational Safety and Health notes that under typical laser class 2 conditions responded only 17% of subjects with a blink reflex and thus this reflex as the only protective mechanism at exposure to laser radiation of this class by no means sufficient. In the BGI ( BG info) 832 "Operation of laser products" dated April 2003, stated: " The existence of the blink reflex to protect the eyes must not be assumed in general Therefore, one should, if laser class 2 radiation enters the eye. deliberately close their eyes or turn away immediately. " The Lidschlussreflexzeit is dependent of many factors, including. The size of the light spot on the retina The accident prevention regulations (UVV) " laser radiation" BGV B 2, however, is still of a blink reflex after 250 ms and thus precludes the knowledge produced by research.

Influences on the eyelid closure

The reflex no longer occurs in both failure of the afferent and the efferent limb. With a local anesthetic on the eye it is an indication of their effectiveness. It can also be used as a criterion for assessment of the anesthetic depth. In a facial paralysis it also comes to an absence of the reflection, but not the absence of the so-called Bells phenomenon, which is characterized by a raising of the eyeball according to the above with appearance of the sclera of the eye in an attempt of closure.

When paralytic lagophthalmos occurs due to the paralysis of the ciliary muscles to the inability of the full Lidschlusses. The eyelid closure is permanently (eg blindness) or short term (eg influence of irritants such as capsaicin ) a.

An induced lid closure also creates two different phenomena:

• The Bell's phenomenon, which manifests itself in the involuntary movement of both eyeballs upward and outward, a position which they occupy even during sleep
• The Westphal - Piltz phenomenon that expresses itself in a narrowing of the pupil size.

Contact lens wearers

Only due to the fact that it is the blink reflex is a reflex foreign ( and not a self -reflection ), it is possible to use contact lenses without holding the eyelid to the eye. Contact lens wearers get used to from this reflex and can then directly touching the cornea.