The pupil is the central aperture of iris, formed by the circular muscle, bordered with pupillary margin and regulating light flow penetration into the inner mediums of the eye. The pupil of the eye, and it's photo-reaction, are visible reflections of the functional state of different brain structures. They combine the information about both afferent (somatic) and efferent (vegetative) components of cranial-cerebral innervation and pupilomotor systems of the eye, and is an accessible and informative object in the evaluation of truncus cerebri activity. Pupil reflexes play the primary role in making a diagnosis of many neurological diseases, being a part of well-known syndromes: Bernard-Horner, Adie's, Argylle-Robertson, Parinoud's etc. Changes of color, dimensions, shape, position of center, equality and reflector reactions of pupils all have clinical significance.
The degree of pupil tension or relaxation is determined by the central nervous system. If the pupil is too lax (relaxed) and shows poor tone, this would reflect on the whole body being fatigued. If the pupil is too constricted (tense), the muscle fibers of the iris reflect a tension experienced by the whole body. The pupil tonus is represented via the ventral and autonomic nervous system. Dilation and contraction are influenced by physical and mental responses of varying kinds, such as fear, pain, excitement, boredom and fatigue.
Color of the pupil
Normal Black Color
The color of the pupil depends on the state of the crystalline and the anterior chamber of eye. In their turn, changes of the crystalline and anterior chamber are the consequences of the pathology of organism's functional systems (endocrine, vascular et al). All deviations of the crystalline color from black are interpreted as pathological changes.
Most often the loss of normal black color takes place in the cataract. In this case, the color can vary from muddy-gray to bright-white with different pronunciation and area of distribution (general whitish tint or separate sub-capsule patches, dots in the center of pupil, radial torches and sector-shaped strips, changes of iris shade in the side illumination).
Dimensions of the pupil
This curve represents changes of pupil diameter depending on the age.
The diameter of the pupil in normal conditions varies within the limits 2.7-4.8 mm in the dark (22.5-40 % of iris diameter), on average 3.5 mm (approximately 29 % of iris diameter). In newborns, pupils are physiologically narrowed (2.32±0.05 mm, that is 19 - 20 % of iris diameter). From the second month, the pupils increase in size gradually on average by 64 % up to the 6-th month, and more by 8.6 % to 1st year of age. This process takes place within 10-11th years. By 10-14th years of age, the opposite dynamics is observed, which can be subdivided into 3 periods. During the first period (15-24th years), pupil dimensions are decreased considerably by 17-19 %. In the course of the second period (25-50th), narrowing is going less intensively (on average by 6 - 9 % every 5 years). During the third period (50-80th years), the pupils are relatively narrow (2.63±0.06 mm - approximately 22 % of iris diameter) undergoing the following smaller decrease of their diameter, which is 3 - 4 % each ten years.
Information about the aging transformations of pupil sizes makes it possible to understand both physiological and pathological miosis and mydriasis syndromes.