What is another word for iris sphincter muscle?
Pronunciation: [ˈa͡ɪɹɪs sfˈɪŋktə mˈʌsə͡l] (IPA) 
The iris sphincter muscle is a muscle located in the eye's iris. It contracts and dilates the pupil, allowing light to enter the eye. There are several synonyms for the iris sphincter muscle, including the sphincter pupillae muscle or simply the pupillary sphincter. It is also referred to as the circular muscle of the iris or the smooth muscle of the iris. Regardless of the terminology used, this muscle plays a vital role in regulating the amount of light that enters the eye, making it an essential part of the visual system. Without the iris sphincter muscle, our eyes would not be able to adjust to varying levels of light in our surroundings.
