The Pupil

The pupil is the central aperture of the iris, formed by the circular muscle, bordered with the pupillary margin and regulating light flow penetration into the inner mediums of the eye.

The pupil of the eye and its photo-reaction are visible reflections of the functional state of different brain structures. Information is combined about both afferent (somatic) and efferent (vegetative) components of cranial-cerebral innervation and pupilomotor systems of the eye, and the pupil is an accessible and informative object for evaluating truncus cerebri activity.

Pupil reflexes play the primary role in making a diagnosis of many neurological diseases as a part of well-known syndromes: Bernard-Horner, Adie’s, Argylle-Robertson, Parinoud’s etc. Changes in the pupil of color, dimensions, shape, position of center, equality and reflector reactions all have clinical significance.

Deformation of Pupils

Under normal conditions, pupils have a regular round shape with even edges. Pupil deformation, in most cases, is associated with local diseases of the iris. But such deviations can also take place in the dysfunction of the innervation components of the pupilomotor system at all its levels. It is necessary to state the difference between the deformation as a consequence of the dystrophic processes, caused by a local disease, and the dystrophy, developed reflexively as a consequence of diseases of internal organs and the central nervous system. Several types of pupil deformations can be distinguished:

* Drawing (oval-elliptic forms)

* Local flatness (sector deformations)

* Multiformity

Such changes of pupil configuration, observed in one eye, in most cases, are a symptom of pathology and when observed in both eyes, the signs of hereditary predisposition.

Deformed pupils, caused not by the shift of pupillary belt stroma, but by “melting” of some parts of the pupillary margin, are considered to be false variants. Most irido-diagnosticians interpret such changes in connection with the symptoms of those organs, whether reflexogenic zones are situated in the iris sectors, adjacent to the deformed areas of the pupil (pupillary area) or situated at the same direction (ciliary area). Multiform deformations are found mostly in patients with brain tumors.

Pupillary flatness, not less than one sixth of pupil circumference, is considered to be significant in showing active pathology. utilizes biometric data analysis to determine several parameters of the pupil including Miosis, Mydriasis, Anisocoria,
Deformation of Pupils (drawing in-out, oval-elliptic forms, local flatness, sector deformations, decentrations and Multiformities).

In normal conditions, the pupils are round in shape with even edges. Deformations of pupils in most cases are associated with local diseases of the iris. But such deviations can also take place in the dysfunction of the innervation components of the pupil motor system at all levels. It is necessary to distinguish the difference between the pupil deformation as a result of local disease or disease of the internal organs affecting the central nervous system.

Changes in the pupil observed in one eye in most cases are the symptom of the disease and when observed in both eyes, may be an indicator of hereditary predisposition. There are eight types pf pupil deformations:

Pupil Decentration and Multiformaties

In a normal state, the pupils are situated in the center of the iris or are slightly shifted inwards and downwards. Such location is conditioned on the balanced interaction between the sympathetic and parasympathetic components of the pupil-motor system. In cases of long-term and stable changes in the organs, and, consequently, viscero-iridal impulses that can occur, injury to neuro-muscular elements of the iris develop.

Fragmentary weakening and elimination of adrenergic mechanism functions lead to violating of the relationship between sphincter and dilator and “pulling” of a pupil. In this event, neither the pupil circle nor the autonomous wreath is deformed.

Decentration is considered to be significant for making diagnoses if the deviation of a pupil center from the iris center is more than 3%.


Pupil dimensions depend on the age, extent of eye illumination, emotional state, exogenous and endogenous intoxications, diseases of the central and peripheral nervous systems and many other factors.

It should be taken into consideration at examination that our organism is not perfectly symmetric: small differences in the dimensions of pupils are quite common. Almost one quarter of the human population have clinically significant anisocoria (up to 0.5 mm, that is, up to 4% of iris diameter). This phenomenon becomes more pronounced with the age: such anisocoria takes place in one fifth of people up to 17 years and in one third people older than 60 years.

The extent of anisocoria is not constant; it can change (increase or decrease) in time,. When this happens, the pupil size can be bigger either on one or the other side.

If the difference between pupil sizes is decreased in bright illumination, is not a manifestation of some disease and is not accompanied by the other symptoms, then, this difference is not a pathological symptom and is called “simple” anisocoria.

True anisocoria, in most cases, is a symptom of the injury of not only the central nervous system, but also of many internal organs. Anisocoria is observed in different diseases of the central nervous system (encephalitis, neurosyphilis, cerebral blood circulation disorders, brain tumors, basal arachnoiditis, cranio-cerebral traumas and multiple injuries in the cervical part of the spinal cord) as well as in internal diseases (injuries to the lung apex, calculous cholecystitis, urolithiasis and appendicitis).

In the case of visceral diseases, dilation of the pupil is associated with the reflector action on the boundary sympathetic trunk. Thereby, changes of the pupil are indicative of possible pathology of internal organs of the same side if there is no neural pathology.

Pupil Mydriasis

The pupil is chronically large at all times and is effected by the sympathetic nervous system.

Dilation of pupils – mydriasis – when in daylight or artificial illumination, their diameter is more than 4 mm (that is more than 33 % of the iris diameter), and can be caused by several reasons:

* Paralysis of the pupils sphincter in the injury of parasympathetic pupil innervation (no reaction on light, piloracpine does not have the influence on the diameter of pupil);

* Irritation of sympathetic pupil innervation (spastic option of mydriasis – in so doing the reaction on light still be present);

* Dysfunction of pupils sphincter in case of not working afferent pupillary neurons, and, to the lower extent, mesencephalic internuncial neurons (pilocrpine stimulates constriction of pupils).

Mydriasis, or dilation of the pupils, occurs normally in daylight or artificial illumination. When the pupil diameter is more than 4 mm (more than 33% of the iris diameter), mydriasis can occur for several reasons:

* Paralysis of the pupil sphincter in the injury of parasympathetic pupil innervation (no reaction to light, pilocarpine does not have influence on the diameter of pupil)

* Irritation of sympathetic pupil innervation (spastic option of mydriasis, a state in which the reaction to light can still be present)

* Dysfunction of pupil sphincter in the case of non-working afferent pupillary neurons, and, to a lower extent, mesencephalic internuncial neurons (pilocarpine stimulates constriction of pupils)

The reasons for physiological mydriasis, besides those similar to physiological miosis (constitution, age, refraction), can be as follows:

* Sexual (differences no bigger than 0.25 mm, take place only in people with light eyes)

* Pain (associated with the increased secretion of adrenaline)

* Emotional (pleasure, fear, irritation, anger, indignation, increased attention, desire etc.)

* Vestibular-pupillary (irritation of vestibular apparatus causes long dilation of pupils after small transient constrictions)

* Cochleo-pupillary

* Promortal (moment of death and first two to three hours after it)

Pathological mydriasis appears because of different etiologic and pathogenetic factors:

* Comatose states (thyrotoxic, epileptic, eclamptic, liver, hypochlorinemic)

* Endocrinopathy (Basedow’s disease)

* Severe infectious diseases (botulism)

* Lingering pain syndrome

* Irritation of meningeal membrane (Flatau symptom)

* Visceral diseases, accompanied by hyperthermia, hypertensive crisis, dyspnea

* Intoxications (alcohol, narcotic hallucinogen, carbon disulfide, dinitrophenol, etc.)

* Pharmacological action (adrenomimetic drugs, anticholinergic novocain etc.),

* Hysterical fit (Raedlich’s symptom)

* Associated conditions including adrenal exhaustion, urinary tract disorders, bronchial disorders, and faulty digestive systems.

Unilateral mydriasis is of interest for topic diagnosis of the central nervous disease system and is a part of a number of syndromes: Pty’s, Notnaghel’s, superior orbital fissure, external wall of sinus cavernous, Webber’s, Benedict’s, neuritis of optic nerve and paralysis of oculomotor nerve, as well as post-traumatic encephalopathy.

Diagnosis of unilateral miosis or mydriasis, which is a part of multi-component clinical syndromes, is rather easy. Difficulties take place in differential diagnoses of mono-symptom and isolated unilateral miosis or mydriasis. In such cases, pharmacological tests are applied (adrenaline or homatropine).

Pupil Miosis

The pupil is chronically small at all times. This indicates a constriction. It is stimulated by the parasympathetic nervous system. Primary cause of pupillary miosis can include opioids or narcotics, hypertension medications, horner syndrome, head injury, inflammation of the eye (anterior uveitis) and exposure to pesticides.

Constriction of pupils, or miosis, develops in the case of injury to or irritation of the vegetative innervation of pupils. This state can be verified if the diameter of the pupil is equal to or less than 2.5 mm (that is less than 21% of the iris diameter). There are two types of miosis: paralytic, depending on the injury of the pupil dilator due to the block of its sympathetic tracts, and spastic, connected with the spasms of the pupil sphincter as a result of its parasympathetic tract irritation.

Physiologic miosis depends on the following factors:

* Constitution (hyper-pigmentation of irises, parasympathicotonicity, balance of cholinergic and adrenergic systems)

* Age (the extent of wear of adaptive-protective forces of the organism, both metabolic and tissue, for example, iris atrophy)

* Vagotonic factors (the state of transitory parasympathicotonia: mental-physical fatigue, hyperventilation, sleep, periods after eating meals)

* Psycho-emotional state (mobilization of all forces of the organism, for example, an aggressive attack)

* Refraction factor (hypermetropes pupils are somewhat more narrow than in emmetropes, and in emmetropes  more narrow than in myopes)

Pathological miosis appears under the influence of different factors, acting on the cortico-truncal vegetative centers:

* Exogenous intoxications (pharmacological – carbocholine, pilocarpine, eserine, pyrophose, morphine etc.; alcohol; carbon monoxide)

* Endogenous intoxications, causing comatose states (uremic, diabetic, alimentary, dystrophic)

* Astheno-depressive psychosis

* Acute violations of cerebral blood circulation

* Hypofunction of the vegetative nervous system, leading to the hypofunction of the other organs (for example, digestive tract)

Unilateral miosis is of great importance for topic diagnosis of injuries of the central nervous system, especially in the vertebro-basilar basin.

Many primary and secondary syndromes of the injury in these areas include: Bernard-Horner’s, Dejerine-Klumpke’s, Pancoast’s, Babinski-Naugeot, alternating bulbar Wallenberg-Zakharchenko’s etc.

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