The pupil is located in the very center of the iris (it is black), it forms a round opening through which light passes to create the image we see.
When staying in bright light, the pupil narrows, the diameter of the pupil is about 2 mm, and in low light it widens up to 8 mm. The smaller the pupil, the larger the iris, and the resulting image is better because the influence of spherical aberrations is reduced. This mechanism enables the entry of a sufficient amount of light, or light signals, which will be converted into vision, and at the same time protects the retina and other structures of the eye from possible light damage. The regulation of the expansion (diameter) of the pupil is performed by two muscles located in the iris, namely Musculus dilatator pupillae (muscle dilator pupillae), which dilates the pupil in the dark so that enough light signals reach the retina, Musculus sphincter pupillae (muscle constrictor pupillae), which it narrows the pupil in large amounts of light so that too much light does not enter the eye and thus protects the retina from damage.
The term mydriasis refers to pupils wider than 6 mm, and mydriatics represent the drugs we use to dilate the pupil.
The term miosis refers to pupils smaller than 2 mm, and miotics are drugs that constrict the pupil.
Autor:
bc. Livio Svržnjak, optometrist
