Which cranial nerve is assessed when patients are asked to read an eye chart?

When patients are asked to read an eye chart, the cranial nerve being assessed is cranial nerve II, which is the optic nerve. This nerve is primarily responsible for vision, as it transmits visual information from the retina of the eye to the visual cortex within the brain. By asking a patient to read from an eye chart, the examiner is evaluating the function of the optic nerve and assessing the acuity of the patient's vision.

Cranial nerve III, known as the oculomotor nerve, is involved in eye movements and controls most of the eye's movements, as well as pupil constriction. Cranial nerve IV, the trochlear nerve, innervates the superior oblique muscle, contributing to eye movement as well, while cranial nerve VI, the abducens nerve, is responsible for lateral eye movement. While these cranial nerves are important for overall eye function and movement, they do not specifically relate to the ability to perceive visual detail, which is what reading an eye chart assesses. Thus, the primary nerve evaluated when reading an eye chart is cranial nerve II.