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Los eyes they are a very powerful tool to successfully function in nature and go far beyond simply providing a vision of the world. The membrane that gives color to the eyes, the iriscontracts or dilates depending on the ambient light and the window through which the light penetrates is what we know as pet.
Its geometric arrangement has been the subject of debate for a long time. In 2015, a group of researchers from the University of Berkeley (California) carried out a detailed study aimed at answering why animals have different types of pupils.
To do this, the scientists analyzed the shape of the pupil of more than two hundred different terrestrial species and concluded that the pupillary morphology was directly related to the ecological niche of the animal.
Vertical pupil helps ambush
These researchers observed that the vertical slit pupil is a general pattern of predators, animals that hunt furtively and have to remain motionless for a long time watching their prey. This type of pupil is the one that, for example, cheetahs have.
This pupillary arrangement allows them to control the entry of light much better and calibrate with great precision the distance that separates them from their prey without having to move their heads. Vertical pupils are useful to know the probability of success and whether or not the energy expenditure of the race is worth it.
Thanks to the vertical pupil, they can calculate the depth of field through two mechanisms: measuring the degree of blurriness of the objects located in front and behind the focused object, and measuring the distance of the objects through the three-dimensional image that it is capable of. rebuild the brain from the information it receives from each retina (estereopsis).
Rectangular pupils for panoramic vision
Las gazelleslike most ungulate mammals, have rectangular pupils with a horizontal disposition, with which they see more clearly what is on the ground plane, calculating the precise moment in which they have to start the race.
Thanks to this pupil arrangement, more light enters from the sides than from above or below, generating a panoramic vision with which they are able to detect the presence of predators. The horizontal pupil also improves the image quality of objects and helps the eye get less glare from overhead.
Some herbivores have taken an additional evolutionary step and have elongations in the upper part of the eye, the so-called corpus nigra or iridic granules, which act as a visor to minimize the entry of light that comes from above and avoid glare.
On the other hand, herbivores enjoy an ocular adaptation known as cyclovergence, which basically consists of the eyeball rotating in the eye socket so that the long axis of the pupil is always parallel to the ground plane. This singularity allows their eyes to always observe the distance, regardless of whether they are grazing or not.
Additionally, the eyeballs are situated on either side of the head to provide a much larger field of vision, with a single blind spot located behind its hindquarters. This makes it possible to explain, for example, why horses, when they sense danger behind them, defend themselves by kicking.
Round and ‘W’ shaped pupils
There are animals, like lobos, which do not require such a complex optical device since their hunting tactic is diurnal and consists of exhausting their prey. For this reason, like us, they have rounded pupils.
Of all the types of pupils, perhaps the most amazing is that of the sepias (Sepia) that adopts a practically circular shape when the animal is in dark environments and in a ‘W’ shape when there is a lot of light, with which it amplifies the contrast of the image and more accurately assesses the distance at which it is found The prey.
To finish, the geckos Night owls have an irregular, jagged-looking pupil that helps them hunt in a variety of environments. And it is that the popular saying already says, the eyes are the mirror of the soul.
Pedro Gargantilla is an internist at El Escorial Hospital (Madrid) and the author of several popular books.
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