Final answer:
The combining form shared by the terms ectiris, choroidoiritis, and iralgia is 'ir'. It refers to the iris, which is involved in regulating the size of the pupil and controlling the amount of light that enters the eye. The terms ectiris, choroidoiritis, and iralgia describe different conditions related to the iris and eye pain.
Step-by-step explanation:
The combining form shared by the terms ectiris, choroidoiritis, and iralgia is 'ir'.
The combining form 'ir' refers to the iris, which is the colored part of the eye. It is involved in regulating the size of the pupil and controlling the amount of light that enters the eye. In the terms ectiris, choroidoiritis, and iralgia, 'ir' is combined with other word parts to describe different conditions related to the iris and eye pain.
For example, ectiris refers to inflammation of the iris, choroidoiritis refers to inflammation of both the iris and the choroid (a layer of the eye), and iralgia refers to pain in the iris or eyepain.