Which cranial nerve is tested using a Snellen chart?

The correct answer is based on the function of cranial nerve II, also known as the optic nerve. This cranial nerve is primarily responsible for vision, and its assessment is crucial in determining an individual's visual acuity. The Snellen chart is a standard tool used in clinical settings to measure how well a person can see at various distances, effectively testing the function of the optic nerve.

During the examination, the patient is instructed to read letters of different sizes from a specific distance, which helps to assess how well the optic nerve is transmitting visual information from the eye to the brain. A decline in visual acuity or any abnormalities detected during this test may suggest issues with the optic nerve or the visual pathways.

The other cranial nerves listed serve different functions: cranial nerve I is involved in the sense of smell, cranial nerve VI controls lateral eye movement, and cranial nerve VII is responsible for facial expressions and some aspects of taste. Therefore, the connection of cranial nerve II to the Snellen chart makes it the correct choice in testing visual capabilities.