Corpus: Pupil

In veterinary medicine, the term pupil is used to describe the eyehole bounded by the iris, through which light penetrates the inside of the eye and thus reaches the retina.

The pupil is a recess in the iris tissue. The size of the eye hole is thus changed by contracting or relaxing the iris muscles.

In domestic mammals, just as in humans, the pupil is round at maximum dilation. During the constriction of the eye hole, this circular shape is only maintained in dogs, large wild cats and also approximately in pigs. The pupil of ruminants and horses is an elongated transverse oval, whereas in the domestic cat it is a high vertical slit.

The size of the pupil and the amount of light reaching the retina is regulated by the sphincter and dilator pupillae muscles of the iris. A contraction of the dilator pupillae muscle causes the pupil to dilate, while contractions of the sphincter pupillae muscle cause it to constrict.

Through the so-called pupillary reflex, the incidence of light in the eye directly controls the contraction of the iris muscles and thus indirectly the size of the pupil.

• Salomon FV, Geyer H, Uwe G. 2008. anatomy for veterinary medicine. 2nd, updated and expanded edition. Stuttgart: Enke Verlag in MVS Medizinverlage Stuttgart GmbH & Co. KG. ISBN: 978-3-8304-1075-1