The canthus is the angle where your upper and lower eyelids meet. You have two on each eye: the inner (medial) canthus near your nose and the outer (lateral) canthus near your temple. These small corners do far more than frame the visible eye. They anchor tendons that hold the eyelids taut, house part of the tear drainage system, and serve as landmarks for everything from facial recognition to surgical planning. The anatomy packed into each canthus is surprisingly complex, and problems in the area can affect both how you see and how you look.
What Sits Inside Each Corner
The medial canthus, the inner corner, is the busier of the two. Beneath the skin lies the medial canthal tendon, a fibrous band that connects the orbicularis oculi muscle (the muscle you use to blink and squeeze your eyes shut) to the bone of the nasal bridge. This tendon keeps the inner eyelid firmly pressed against the eyeball. Cadaveric measurements show the medial canthal tendon sits in a tight relationship with the lacrimal sac, the small pouch that collects tears before they drain into the nose. The upper rim of the tendon consistently falls below the top of the lacrimal sac but above the sac’s internal fornix, with distances between these landmarks averaging roughly one to two millimeters.
1PubMed. The Relationship Between Lacrimal Sac Fundus, Lacrimal Sac Lumen Fornix, and Medial Canthal TendonTucked into the medial canthus you can also see the caruncle, that small, fleshy pink mound. It is a piece of modified skin tissue containing hair follicles, sweat glands, sebaceous glands, and accessory lacrimal glands.
2Diagnostic Pathology. Histopathological study of lesions of the caruncle: a 15-year single center reviewThe lateral canthus, at the outer corner, has a somewhat simpler anatomy but its own set of surgical challenges. It is anchored to the lateral orbital wall by the lateral canthal tendon. Identifying its exact insertion point matters during reconstructive surgery. In imaging studies, the lateral canthal insertion sat an average of about 4.4 mm from the lateral orbital margin and roughly 13.9 mm above a bony reference point called the Jugale. The height of this insertion was strongly predicted by the overall height of the lateral orbital wall, meaning orbital bone shape determines exactly where the outer corner of the eye is anchored.
3PubMed Central. Anatomy of the lateral orbital wall: A topographic investigation for identification of the lateral canthal attachmentHow the Canthus Helps Drain Your Tears
Every time you blink, your eyelids do not just spread tears across the cornea. They also pump used tear fluid out of the eye and into the nose. The machinery behind this lives at the medial canthus. The tiny openings visible at each inner lid margin, called puncta, lead into narrow channels (canaliculi) that funnel into the lacrimal sac. From there, tears travel down the nasolacrimal duct and empty behind your nose, which is why your nose runs when you cry.
A small muscle called Horner-Duverney’s muscle, attached to the medial canthal tendon, drives this pump. When the muscle contracts during a blink, it squeezes the first two-thirds of the canaliculi shut, pressing tear fluid toward the lacrimal sac. The inner third of the channels and the sac entrance are then compressed from behind as the muscle shortens and thickens, pushing fluid further along the path.
4PubMed. New insights into the lacrimal pumpOther connective tissue structures near the medial canthus act as counterforces to this muscle contraction. The medial horn and a sheet of tissue called the capsulopalpebral fascia pull against the orbicularis muscle during the pumping cycle, creating the push-and-pull action that keeps tear drainage moving efficiently.
5PubMed. The medial horn and capsulopalpebral fascia in the medial canthus are significant antagonists of the orbicularis oculi muscle for lacrimal drainageWhen this system fails, the results are immediately noticeable: chronic watering of the eyes, recurring infections, or crusting along the inner lid margin. Surgeons who operate on the lacrimal system need precise knowledge of the medial canthal tendon’s position relative to the lacrimal sac, because placing an incision even a couple of millimeters too high or too low can miss the target or damage supporting structures.
The Epicanthal Fold and Why Inner Canthi Look Different Across Populations
An epicanthal fold is a crescent of skin that partially covers the inner canthus. It is one of the most visible sources of variation in eye appearance worldwide. Early in embryonic development, all human eyes begin with lateral placement on the head. Between the fifth and ninth weeks, they migrate medially. As this happens, the orbicularis muscle converges near the medial canthus, and a fold of skin forms over it. This fold appears in all fetuses at roughly three to six months of gestation and typically regresses before birth in most populations of European descent, especially as the nasal bridge grows and pulls the skin taut. In most East Asian populations, the fold persists into adulthood. Researchers attribute this to a relatively flatter nasal root combined with an excess of horizontal skin at the medial canthus relative to a vertical shortage.
6PLoS ONE. Relationship between lower eyelid epiblepharon and epicanthus in Korean childrenEpicanthal folds are sometimes visible in infants of European descent who have a low nasal bridge, but they are rare after adolescence in those populations. The fold’s presence or absence does not affect vision; it is a normal anatomical variation. It does, however, influence how the inner canthus looks and how measurements like intercanthal distance are perceived. A prominent fold can make the eyes appear closer together even when the bony distance between the orbits is perfectly average.
Canthal Measurements and Facial Proportions
Clinicians and surgeons rely on several canthal measurements when assessing the face. Inner intercanthal distance is the span between the two medial canthi. Outer intercanthal distance measures from one lateral canthus to the other. Canthal tilt describes whether the lateral canthus sits higher or lower than the medial canthus, giving the eye opening its upward or downward slant.
These measurements differ systematically across populations and between sexes. A three-dimensional imaging study comparing young Caucasian and Chinese adults found that Caucasian males had larger palpebral fissure heights, greater canthal tilt, and larger lateral canthal angles, while Chinese males had greater inner and outer intercanthal distances. Similar patterns held for women, with Caucasian females showing wider palpebral fissures and steeper canthal tilt, and Chinese females having wider intercanthal spacing.
7PubMed Central. Racial and sexual differences of eyebrow and eyelid morphology: three-dimensional analysis in young Caucasian and Chinese populationsPerceptions of attractiveness are also linked to canthal geometry. A biometric study across multiple ethnic groups found that attractive Asian faces tended to have a less steep palpebral slant compared to the average Asian face, while attractive Caucasian and African faces had a steeper slant than average. Across all groups, faces rated as attractive tended to have wider-set eyes.
8PubMed. Biometric study of eyelid shape and dimensions of different races with references to beautyTelecanthus Versus Hypertelorism
When the inner canthi are spaced unusually far apart, two distinct conditions can be responsible, and confusing them has real clinical consequences. Telecanthus (sometimes called pseudo-hypertelorism) means the soft tissue of the medial canthi is displaced outward, making the eyes appear widely separated, but the bony orbits are in a normal position. True orbital hypertelorism means the bony eye sockets themselves are too far apart.
9PubMed Central. HypertelorismThe distinction matters because the treatments are completely different. Correcting telecanthus is a relatively straightforward soft-tissue procedure involving the medial canthal tendon. Correcting true hypertelorism requires moving the bony orbits closer together, which means major craniofacial surgery involving both the skull and the face. The terminology in the literature has been historically confused, with different authors using different definitions for the same measurements, so clinicians have worked to standardize the language.
10PubMed. Telecanthus and hypertelorism in frontoethmoidal meningoencephaloceles and the surgical correction of these conditionsWhat Happens to the Canthus With Age
Aging loosens the canthal tendons, particularly the lateral one. As the tendon stretches, the lower eyelid loses its grip against the eyeball. This is one of the main causes of involutional ectropion, a condition where the lower lid turns outward, exposing the inner lining. The eye dries out, becomes irritated, and tears spill onto the cheek instead of draining through the puncta. Multiple factors contribute, including both horizontal laxity of the lid and vertical traction from surrounding tissue changes.
11PubMed Central. Involutional ectropion: etiological factors and therapeutic managementAt the medial canthus, similar laxity can pull the inner lid away from the eye, disrupting the tear drainage mechanism. The medial tarsal strip procedure addresses this by repositioning and tightening the medial lower or upper eyelid to restore normal anatomy. Standard medial canthal tendon plications (essentially folding and stitching the tendon tighter) have been attempted but often lack permanence and fail to achieve proper posterior and medial placement of the canthal angle.
12JAMA Network. The Medial Tarsal StripAt the lateral canthus, the lateral tarsal strip procedure has become the most commonly performed and effective surgery for correcting horizontal eyelid laxity. In a ten-year review of lower blepharoplasty with routine lateral canthal support, the rate of lid malposition requiring a second operation was about 3.5 percent. The most common complication was chemosis (swelling of the conjunctiva), occurring in roughly 12 percent of patients, while more serious problems like orbital hematoma were rare.
13Plastic & Reconstructive Surgery. Primary Transcutaneous Lower Blepharoplasty with Routine Lateral Canthal Support: A Comprehensive 10-Year ReviewSkin Cancer Near the Inner Canthus
The medial canthal region is a common site for basal cell carcinoma, the most frequent type of skin cancer. This area gets cumulative sun exposure, and the concave contour of the inner canthus means tumors here can grow inward along the lacrimal pathway before they become obvious on the surface. If a tumor is not completely removed, it tends to recur or spread deeper along these channels.
14PubMed Central. Utility of the Glabellar Flap in the Reconstruction of Medial Canthal Tumors after Mohs SurgeryReconstruction after tumor removal in this area is especially difficult. The medial canthus sits at a convergence of skin with different thickness, texture, and mobility. A patch of skin from the forehead does not match the thin, delicate skin near the nose, and the contour is concave rather than flat, making it hard to lay a flap smoothly. Surgeons have developed various local flap techniques, including glabellar flaps (using skin from the area between the eyebrows) and combinations of advancement and rotation flaps, to cover defects while maintaining both the structural integrity of the lid and an acceptable cosmetic result.
15International Journal of Dermatology and Venereology. Treatment of Basal Cell Carcinoma Involving the Medial Canthus by Multiple Local Flaps: A Case ReportRepairing a Torn Medial Canthal Tendon
Trauma to the inner canthus, whether from a dog bite, a car accident, or a fall, can sever the medial canthal tendon and damage the tear drainage channels simultaneously. This is one of the more challenging injuries in facial surgery because you need to restore three things at once: the structural anchor of the lid, the patency of the lacrimal system, and a clean lid margin. The recommended sequence of repair starts with intubating the lacrimal canaliculi to keep them open, then reattaching the medial canthal tendon to bone, and finally repairing the lid margin. Following this order gives the best chance of preserving both tear drainage and a sharp lid angle.
16FPSAM Video Journal. Complex Medial Canthal Tendon Laceration: Sequence of RepairCosmetic Epicanthoplasty
Epicanthoplasty is the surgical modification of the epicanthal fold to expose more of the inner canthus. It is one of the most commonly requested cosmetic procedures in East Asia, often performed alongside double-eyelid surgery. The technical challenge is that simply cutting away the fold tends to leave visible scars, because the skin at the medial canthus is under tension from the underlying orbicularis muscle and a fibrous band beneath the fold.
A recently described five-step technique focuses on releasing this tension before designing any skin flap. The surgeon removes the fibrous band beneath the fold and releases the orbicularis muscle, then performs a traction test: pulling the skin toward the nose to confirm the fold has disappeared. Only then is the remaining wound closed with a flap tailored to the actual wound shape. This “tension release first” approach is a departure from older methods that pre-planned the flap geometry before making any incision.
17PubMed Central. The five-step medial epicanthoplasty: simple and standardizedAn alternative approach, the adjustable V-flap epicanthoplasty, has been performed on hundreds of patients. This technique uses a V-shaped skin incision combined with a layered procedure: cutting the skin, then the muscle, then plicating (tightening) the medial canthal ligament to reshape the inner corner of the eye. The layered approach allows the surgeon to adjust the final lid position during the procedure rather than committing to a fixed design from the outset.
18PubMed. Adjustable V-Flap Epicanthoplasty Based on Desired Eyelid MorphologyAngular Blepharitis at the Lateral Canthus
The lateral canthus is prone to a specific form of eyelid inflammation called angular blepharitis: redness, scaling, and cracking of the skin right at the outer corner of the eye. The usual culprits are bacteria, most commonly Staphylococcus and Moraxella species. Treatment typically involves antibiotic ointment applied to the area.
When angular blepharitis does not respond to standard therapy, a less obvious cause may be at work. Demodex mites, tiny parasites that live in human hair follicles, have been identified as a cause of refractory cases. In one documented instance, skin biopsy revealed multiple Demodex folliculorum organisms within hair follicles and on the skin surface, surrounded by pockets of inflammation. The lesson for anyone with persistent, treatment-resistant irritation at the outer corner of the eye is that the mites should be considered, particularly when topical steroids are not helping.
19The American Journal of Cosmetic Surgery. Case of Angular Blepharitis Caused by Demodex folliculorumCrow’s Feet and Botulinum Toxin Injections
The lines that fan out from the lateral canthus when you smile, colloquially called crow’s feet, are technically known as lateral canthal rhytids. They form because the orbicularis oculi muscle contracts every time you squint, smile, or laugh, and years of repetitive folding eventually creases the overlying skin permanently.
Botulinum toxin injections are the most common non-surgical treatment. The toxin relaxes the orbicularis oculi muscle, smoothing the lines. Anatomical research has refined where exactly to place the injections for the best results, mapping the surface landmarks of the muscle fibers responsible for the lines. The injection points are not simply “at the wrinkles” but at specific locations relative to the underlying muscle anatomy and nearby structures, since the orbicularis oculi muscle interacts with other facial muscles in the region.
20PubMed Central. Novel Anatomical Proposal for Botulinum Neurotoxin Injection Targeting Lateral Canthal RhytidsThe Semilunar Fold and Its Evolutionary Past
If you look closely at your inner canthus, you will notice a small, pinkish fold of tissue curving over the inner corner of the eye, just lateral to the caruncle. This is the plica semilunaris, or semilunar fold. In humans it is a modest crescent, but in many other mammals, the equivalent structure is a full third eyelid (nictitating membrane) that sweeps horizontally across the eye to moisten and protect it. Morphological studies of the human semilunar fold at different developmental stages show that its origin from this ancestral third eyelid can still be recognized to a degree, even though it has lost the ability to move or cover the cornea.
21PubMed. The structure of the human semilunar plica at different stages of its development–a morphological and morphometric studyThe fold still serves a minor role: it helps sweep debris toward the caruncle and contributes to tear film management in the inner corner. Occasionally the plica becomes inflamed or develops cysts, but for most people it sits quietly in the medial canthus, a small souvenir of a time when our ancestors could blink sideways.