The outer corner of the eyelids where the upper and lower eyelids meet are rounded instead of joining in a discrete angle. This area is called the outer canthus or the lateral canthus. In most cases, the outer canthus is slightly higher (approximately 2 mm) than the inner canthus, giving the eyelid aperture an upward slope from the inner corner to the outer corner of the eyelids.
The outer canthal angle is formed by tendinous bands that extend from the upper and lower eyelid tarsal plates (connective tissue support structures in the upper and lower eyelids) to the orbital bone underlying the canthal angle. These canthal tendons attach the eyelids to the orbital rim and maintain the shape of the eyelid opening and the canthal angle. Rounding of the outer canthus can be associated with a narrowing of the horizontal eyelid opening.
Causes of lateral canthal rounding
A separation or dehiscence of the lateral canthal tendon from the bone insertion at the outer corner of the eyelids can result in rounding of the lateral canthal angle in addition to a horizontal shortening of the eyelid opening. This may take place with normal aging or after an injury.
Surgery can lead to lateral canthal rounding if scar tissue forms at the junction of the upper and lower eyelids at the outer corner. Lateral canthotomy, when the junction of the upper and lower eyelid angle is split at the outer corner, creates some risk of lateral canthal angle blunting.
A tarsorraphy, or intentional surgical closure of the eyelids (or a portion of the eyelids), can also create a rounded lateral canthal angle.
Often seen with
After eyelid surgery (canthoplasty, blepharoplasty, etc.), normal aging.
What you see in the mirror
The outer corner of the eyelid is rounded instead of meeting at a sharp angle. The horizontal eyelid opening may be narrowed.