Lateral canthoplasty is an operation performed at the outer corner of the eye where the upper and lower eyelid join together known as the lateral canthus. The tendon that holds the joined eyelids to the bone at this point is called the lateral canthal tendon, hence the name "canthoplasty."

In non-Asian patients, lateral canthoplasty is used commonly in older patients to reconstruct a stretched or weakened lateral canthal tendon for the purpose of improving support for the aging lower eyelid.

Asian lateral canthoplasty is an entirely different operation with a confusingly similar name. More accurately, it is a canthotomy, or a roughly horizontal cut made all the way through the lids at the corner.

The procedure is designed to widen the eyelid opening in patients born with lids that seem too short horizontally and especially narrowed or rounded at the outer corner. Not only does the operation have nothing to do with repairing a deficient canthal tendon as in normal canthoplasty, but the very process of Asian lateral canthoplasty may end up weakening normal anatomic relationships around the tendon and predispose to support problems later in life.

Some patients mistakenly believe that lateral canthoplasty is the equivalent of epicanthoplasty but on the opposite side of the eye. Because of eyeball's spherical shape, however, simply widening the eyelids' lateral opening (palpebral fissure) creates an odd gap between the eyeball and any extended lid tissue. Any widening of the fissure must be pulled backwards towards the bone to maintain normal eye/eyelid contact.

Consequently, there is not much visible lengthening effect when the eye is viewed from the front; the slight widening of 1-2 mm is only noticeable in a side profile view. The widened segment has no lashes and so may call attention to itself if makeup is not used as camouflage.

As with epicanthoplasty, the operation requires the creation of tiny flaps and so visible scarring can be a problem. While an interesting approach to lengthening a narrowed fissure, few patients truly benefit from this approach.