What is the term for the angle at either end of the slit of the eyelids?

The term for the angle at either end of the slit of the eyelids is known as the canthus. This anatomical feature is significant in discussing the structure of the eye and eyelids, as it defines the inner and outer corners of the palpebral fissure—the space between the eyelids when they are open. The inner canthus is located where the upper and lower eyelids meet closest to the nose, while the outer canthus is found at the opposite side, towards the temples.

Understanding the canthus is crucial in optometry and ophthalmology because it can play roles in certain procedures and in diagnosing conditions related to the eyelids or surrounding structures. For instance, during eyelid surgeries or assessments of tear drainage, knowledge of the canthi and their positioning can influence surgical outcomes and treatment plans.

The other options refer to different anatomical terms or concepts that do not accurately describe the angles at either end of the eyelid slit. The endothelium refers specifically to the inner layer of cells lining blood vessels or the cornea, while the term "orbital exterior angle" is not recognized in anatomical terminology. An acute angle, while a valid geometric term, does not have a specific relationship to the anatomy of the eyelids.