canthus

Canthus is the anatomical term for the corner of the eye where the upper and lower eyelids meet. There are two canthi: the medial canthus, located at the nasal (inner) corner, and the lateral canthus, at the temporal (outer) corner. The medial canthus contains the lacrimal caruncle and the openings of the lacrimal puncta, through which tears drain into the lacrimal canaliculi and then into the lacrimal sac, continuing via the nasolacrimal duct into the nasal cavity. The lateral canthus forms the outer corner and serves as the attachment point for the lateral canthal tendon, a key component of eyelid support along with the medial canthal tendon.

Anatomy and function: The canthi are maintained by canthal ligaments and surrounding orbicularis oculi muscle. Their configuration contributes to the eyelid aperture and the direction of tear drainage. The distance between the two medial canthi—the intercanthal distance—is used clinically; abnormalities such as telecanthus (increased distance) or hypotelorism (decreased distance) can indicate craniofacial or genetic conditions.

Clinical relevance: Telecanthus and related anatomical variations can be associated with various syndromes or facial dysmorphisms. Surgical procedures involving the canthi, such as canthoplasty, canthotomy, and cantholysis, are used to adjust eyelid position, treat eyelid laxity, or relieve orbital pressure from fractures. The concept of canthal tilt describes the angular relationship of the lateral canthus to the vertical orbit and can have aesthetic implications.