Pupil reflexes (PR):
The diameter of pupils in the constant illumination condition is never the same. It is always oscillating, alternating constrictions and dilations with the amplitude up to 0.5 mm (it is approximately up to 4 % of iris diameter) and the frequency 0.1 - 2 oscillations per second. Spontaneous pronounced oscillations of pupils are called 'hippus'. The amplitude is decreased in the bright illumination and is the largest at the average size of the pupil, when iris has maximum freedom of movements. The increase of oscillations amplitude more than 1 mm (that is more than 8 % of iris diameter) is observed in a number of vascular, inflammatory, degenerative and traumatic diseases of the nervous system. Often it is an early symptom of disseminated sclerosis. The decrease of spontaneous oscillations of pupils ('stone pupils') is observed in the severe neurogenic, mental, visceral and infectious diseases, and also in the terminal states (syncope, shock, sepsis, coma).
Unexpected, almost momentary dilations of the pupil, independent from the external conditions, alternately in one or other eye, are named 'jumping pupils'. In such case, all the other reactions (on light, accommodation, convergention and the action of pharmacological agents) are still normal. This phenomenon takes place rarely, mostly in neurasthenia, epilepsy, myelitis, progressive paralyses, and Basedow's disease.
Pupil reaction on light
Among multiply PR, the most important is pupil reaction on light - direct and associated. Constriction of an illuminating pupil is called direct reaction. Constriction of the pupil when illuminating the other eye is called an associated reaction. The time of pupillary reaction is called pupillary cycle, consisting of 4 parameters: latent period of pupil constriction, time of pupil constriction, latent period of pupil dilation and time of pupil dilation.
A number of violations of pupil reactions, which are the components of the classic syndromes of modern neuropathology, are described. Below some of them are mentioned.
There are three anatomical types of pupil immobility and one reflex type.
Anatomical types of pupil immobility:
1. Amaurotic immobility of pupils. In such type, both direct and associated reactions on light of both pupils do not exist, but accommodation and pupil reaction on closing an eye can still be present. Bilateral amaurotic immobility of pupils takes place as a result of the injury of both retinas or optical tract (both sides) before the primary visual centers. In such case, double-sided blindness occurs. It is associated with considerable dilation of the pupils. If the retina or optical tract of only one eye is injured, than in its illumination there is no direct and associated reaction in it. When the healthy eye is illuminated, the direct and associated reactions are present in the blind pupil. Accommodation reaction can also still be present. It should be taken into consideration that the pupil of the blind eye is always wider. As a rule, amaurotic immobility of pupil is developed after neuritis and atrophy of the optical nerves.
2. Hemianoptic immobility of pupils Wernicke's is caused by the injury of the optical tract before the lateral geniculated body. Illumination of the blind areas of the retina does not cause no direct or associated reaction of the pupil. Such reaction takes place at illumination of the intact parts of the retina. If hemianopsy is caused by the injury, located after branching out of the pupil-motor trunk from the optical one, then hemianoptic immobility of pupils is not present. Thereby, hemianoptic immobility of pupils occurs at the injury of the optical tract, in which the fibers of the optical nerve and light reflexes of the pupil come together.
3. Absolute immobility of pupil is characterized by the simultaneous absence of pupil reactions on light (direct and associated) and accommodation. In most cases it is unilateral and is accompanied by mydriasis. It is originated in the injury of the locomotory oculomotor part of the pupil arch, starting from the nuclei of the oculomotor nerve and reaching the sphincter.
Reflex immobility of pupils (Argylle-Robertson's symptom) can be uni- or bilateral. It includes the absence of pupil reaction on light (direct and associated), more vivid, than in the normal state, pupillary reaction in case of accommodation, miosis, anisocoria, smoothed relief of the iris and its partial depigmentation, sector-shaped atrophy of the iris, and deformation of pupils. At the different stages of the disease, this syndrome is pronounced unequally and with different extent. First of all, pupil reaction on light is violated and its latent period is prolonged. It is going more slowly than in the normal state, and the pupils are less constricted. In some sectors of the iris, the constrictions are pronounced much strongly while in the other they are insignificant. Hyper-reflexia eventually increases and finally the reaction on light disappears completely. There are patients, in which the reaction on light and other symptoms undergoes remission, but after some time aggravation occurs. Besides the true Argylle-Roberson's syndrome of syphilitic origin, there is the false non-specific one, observed in the tumors of brain, encephalitis, cranio-cerebral trauma, disseminated sclerosis, alcoholism et al.
Paradoxical reaction of the pupils is the dilation of pupil at illumination and the constriction of pupils in darkness. The injury of the cortical processes of inhibition, predominantly of paradoxical phase, is the basis of this phenomenon. It is observed in the injury of upper cervical ganglion, paralyses of the oculomotor nerve, and hemorrhage to the brain ventricles.
Myotonic pupil reaction is its slowed constriction during accommodation and convergence after repeated fixing of look on the remote point, the weak pupil reaction on light or its absence. Usually it is observed in one eye in disseminated sclerosis, diabetes, brain tumors, cranio-cerebral trauma.
Neurotonic pupil reaction is slowed constriction during illumination followed by slowed dilation after light is off. It is observed in vegetative neurosis, alcoholism, heavy smoking, and progressive paralysis.
Pupillotonia (Adie's syndrome) is weak pupil reaction on light or its absence, slowed accommodation reaction, and slow pupil dilation up to initial size during long time stay in darkness. Usually it is accompanied with anisocoria, unilateral violations as a rule, cholinegic drugs sphincter's hypersensitivity.
Pupils intravegetative stupor syndrome - is the prolongation of the latent period of dilation. On the pupillogram, in looks as specific plateau in the place of parasymphatic activity transition to symphatic activity. The constriction due to the light action and 'frozen' pupil is its iridologic sign. Apparently, pathogenetic background is the weakening of the cholinergic component and reduction of parasympathetic tonus in chronic alcoholism.
Pupil reactions
Besides the reflex reactions on light, the following pupil reactions are also of interest:
The Cheyne-Stokes respiration pupil reactions are the absence of reactions during pause in respiration, continuously increased dilation of pupils in forced inhalation and consequent fast return to the normal average size when decreasing the depth of breath.
Pupil reaction on accommodation is pupil constriction when looking at the objects close to face and their dilation when looking far. (The accommodation at the small distance is accompanied with convergence of eyes).
Pupil reaction on convergence is the constriction of pupils when eyes are adducted inwards which is usually caused by the approach of an object with fixed look. (The adduction is maximal when object is at 10-15 cm distance from the eyes).
Pupil reaction on pain is their dilation as a response to the pain irritation. (The reflex center for transmission of these irritations to the muscle, dilating the pupil, is the subthalamic ganglion, getting impulses from spinal-thalamic tract).
Trigeminal pupil reflex is characterized by small pupil dilation in irritation of cornea, eyelids conjunctive, or tissues, surrounding eye, which is rapidly followed by pupil constriction (it is provided due to the connection of Y pair cranial nerves with subcortical sympathetic pupil center and additional parasympathetic ganglion of III pair nerves.)
Galvanic pupil reflex is pupil constriction under the action of galvanic current (the anode is placed over the eye or in the temporal area and cathode is placed in the back part of neck).
Cochlea-pupil reflex is bilateral pupils dilation in irritation of vestibular apparatus (rotation etc.)
Pharyngeal pupil reflex is the pupil dilation in case of irritation of posterior pharyngeal wall. (The reflex arc includes glosso-pharyngeal and upper laryngeal nerves);
The pupil dilation takes place when a person is imagining night and darkness (Piltz syndrome) and constriction - when conceiving the sunlight or bright flame (Gaab's syndrome); this reaction is considered to be cortical reflex