Why would an ECP perform a test using the tonometer?

Using a tonometer is specifically designed to measure intraocular pressure (IOP) in the eyes, which is crucial for diagnosing conditions like glaucoma. Elevated IOP can lead to optic nerve damage and vision loss, making this measurement an essential part of a comprehensive eye examination. When the eye care professional performs this test, they are assessing the fluid pressure inside the eye, which helps in determining whether the patient has a normal range of pressure or if there are any abnormalities that require further investigation or management.

While the other options pertain to different aspects of eye health, they do not involve the measurement of intraocular pressure. Analyzing visual acuity focuses on how well a person can see, assessing pupil reaction evaluates how the pupils respond to light, and evaluating eye muscle function tests the coordination and movement of the eyes. None of these directly relate to monitoring pressure within the eye. Thus, the primary purpose of using a tonometer is accurately reflected in the identification of excessive intraocular pressure.