How far horizontally does lateral canthoplasty expand? What we know so far

Lateral canthoplasty is a surgical procedure that expands the outer edge of the eye outward to change the impression of the eye's horizontal width. In textbooks, it is described as potentially changing the dimensions of the palpebral fissure (eyelid opening) by extending the lateral canthus[1]. However, there are no studies showing exactly how many millimeters it expands or what proportion reverts, so this is not a surgery that can be discussed in numerical terms.

What happens at the depth of the lateral canthus?

The outer lateral canthus is not a single ligament but a support structure formed by multiple fibers. In textbooks, it is explained that the lateral canthal ligament, cord-like tissues supporting the tarsal plate, the lateral leg of the muscle that raises the eyelid, and ligaments supporting the eyeball from below come together to form the lateral support mechanism[2]. The lateral canthal ligament has a dual attachment pattern, with the superficial layer attaching to the lateral orbital rim and the deep layer attaching to Whitnall's tubercle on the inner surface of the zygoma[2]. Anatomical studies have also confirmed that this tubercle is an attachment point for multiple tissues including the lateral canthal ligament[3].

How far does it expand? Why we can't provide numbers

There are no quantitative studies demonstrating how much the horizontal width increases. Textbooks state that extending the lateral canthus can change the palpebral fissure dimensions,[1]but they do not provide a value in millimeters. The amount that can be expanded depends on how much space is available at the outer lateral canthus and the positional relationship with the bone edge, so it is influenced by the original shape.[3][2]It is more useful to have a physician examine how much space your lateral canthus has rather than to ask about average values.

Does it revert?

As for reversion, there are also no studies demonstrating the rate of reversion. Since lateral canthus surgery involves cutting the lateral support structure and reconstructing the position, the shape inevitably changes during the healing process[3][2]. The absence of data does not mean the risk is small; it means we cannot quantify the expected outcome. Therefore, it is practical to discuss in advance what to do if reversion occurs.

How is surgery on the medial canthus side different?

The medial canthus involves a separate issue of how to manage the epicanthal fold. Multiple techniques for medial canthal surgery have been reported, and the Japan Plastic Surgery Association guideline also introduces reports that performing it simultaneously with double-eyelid surgery produces more natural results[4]. On the other hand, in Asian patients, there is a tendency for scars to become hypertrophic or discolored more easily, so the visibility of medial canthal scars becomes a common concern, and various techniques to avoid this have been reported[5]. The lateral and medial canthi differ both in the direction they can be expanded and in where scars remain.

Surgery for function versus surgery for appearance

Even with the same lateral canthal surgery, the strength of evidence differs depending on the purpose. In congenital blepharophimosis syndrome where the eyelid opening is naturally narrow, the Japan Plastic Surgery Association guideline states that surgery is expected to not only improve appearance but also reduce the risk of developing amblyopia[4]. However, this is not an evaluation of lateral canthal surgery alone but rather of the overall treatment combining ptosis surgery and medial canthal surgery[4]. We cannot directly apply this effect to cosmetic lateral canthoplasty.

What to confirm during consultation

In surgery involving the lateral canthus, attention must be paid to corneal dryness and exposure due to difficulty closing the eyes. Textbooks also state that in procedures involving this area, corneal exposure and eye dryness become issues and additional procedures such as lateral canthus opening or fixation may be necessary[2]. There are three things to confirm. How much expansion margin your lateral canthus has, where the scar will remain on the outside, and what to do if reversion occurs or the visibility of the white of the eye changes. Because this is an area with limited numerical evidence, please receive an explanation tailored to your own eyes from your physician's consultation before deciding.