9. Februar 2017 - Eye, Ophthalmology

The pupil is a structure of the eye consisting of a hole in the central part of the iris through which light penetrates into the eyeball. It is a dilatable and contractile opening, apparently of black color that has the function of regulating the amount of light that reaches the retina , in the back part of the eye . 1

The size of the pupil is controlled by two muscles: the sphincter of the pupil that closes and is innervated by parasympathetic fibers and the pupil dilator of the pupil that opens and is controlled by sympathetic fibers . Its diameter is between 3 and 4.5 millimeters in the human eye. In the dark it can grow to 5 to 9 mm. There is considerable variation in the maximum size of the pupil between different people ..

Pupillary reflexes

Whytt Reflection

The photomotor reflex of the pupil is examined with a flashlight during neurological examination. This reflex, where the cranial nerves II and III participate , consists of the constriction of the pupil in response to enlightenment . When the light penetrates into one eye, the two pupils constrict in unison ( consensual reflex ) because each retina sends fibers to the optical bands on both sides. 2


  • Pupils of the spine are those with irregular shape.
  • Isocoric pupils in the case that both have the same size.
  • Anisocorous pupils if they are of different size
  • If the pupil reacts to the light decreasing in size we speak of a normoreactive pupil.
  • If the pupil reacts poorly to the light, the pupil is called hyporreactive pupil.
  • If the pupil is dilated it is said to be in mydriasis .
  • If contracted it is said that it is in miosis .
  • Argyll Roberston pupil is a clinical sign consisting of the abolition of the photomotor reflex (contraction of the pupils to the light), with preservation of the reflex of accommodation. It occurs in different diseases, including cerebral syphilis or neurosyphilis .


  1. Back to top↑ Tortora – Derrickson. Principles of Anatomy and Physiology, 11th edition (2006). ISBN 968-7988-77-0
  2. Back to top↑ Schiffman, Harvey (2011). Sensory Perception . Limusa Wiley. P. 246. ISBN  968-18-5307-5 .