What does the canthus refer to in an eye examination?

The term "canthus" refers specifically to the angle at the corner of the eyelids where the upper and lower eyelid meet. In the context of an eye examination, understanding the canthus is important for various reasons, including assessing eye health, determining the proper placement of contact lenses, or performing certain eye procedures.

Recognizing the canthus can help in evaluating conditions such as conjunctivitis or other eyelid abnormalities, as changes in the canthus can indicate underlying health issues. Additionally, the canthus is a reference point for measuring distances in ophthalmic imaging and procedures.

The other options, such as the surface of the cornea, the pupil's size, and the position of the iris, refer to different structural or functional attributes of the eye and do not relate to the anatomical significance of the canthus. Thus, option A accurately captures the definition within the context of eye examination.