The Japanese term Sanpaku literally translates to “three whites.” This visual phenomenon describes an eye where the white part, or sclera, is prominently visible on three sides of the colored iris. This appearance is fundamentally a biological trait resulting from various anatomical factors. Understanding the causes requires examining both common natural variations and specific underlying medical conditions.
Defining the Appearance and Types
Sanpaku eyes are classified based on where the white sclera is exposed relative to the iris. The most common form is known as Yin Sanpaku, where the sclera is visible only beneath the iris. This type is often characterized by the iris resting lower in the eye socket. Conversely, Yang Sanpaku describes the condition where the sclera is visible only above the iris. Upper sclera exposure tends to be a rarer presentation and is more frequently associated with physical changes to the eye or eyelid position.
Natural Anatomical Variation
For many individuals, the Sanpaku appearance is simply a natural, non-pathological anatomical variation. This trait is often influenced by genetics, affecting the size and shape of the eye socket, or orbit. A relatively larger eyeball or a shallower orbit can push the eye slightly forward, increasing the visible surface area of the sclera.
Variations in the positioning of the eyelids also play a large role in creating this look. The marginal reflex distance, which measures the distance between the upper eyelid margin and the center of the pupil, can be naturally shorter or longer. A slightly retracted or higher-set lower eyelid margin can expose more sclera below the iris, resulting in the Yin Sanpaku type. These small differences in bone structure and soft tissue configuration are common. When the appearance is present from birth and does not change over time, it is usually just an aesthetic feature and not an indication of any underlying health concern.
Related Medical Conditions
While often benign, the sudden or progressive onset of a Sanpaku appearance can signal an acquired medical condition that affects the eye or surrounding structures. One of the most common pathological causes is Thyroid Eye Disease, often associated with Graves’ disease. This condition can cause inflammation and swelling of the tissues and muscles behind the eye, pushing the eyeball forward, a condition known as proptosis.
Proptosis can dramatically increase the visibility of the sclera both above and below the iris. Furthermore, the disease process can cause upper eyelid retraction, where the eyelid muscle pulls back abnormally, resulting in a pronounced Yang Sanpaku appearance. This change is often asymmetrical and develops over time, making it distinct from a lifelong anatomical variation.
Changes in muscle or nerve function that control the eyelids can also be responsible. Severe ptosis, or a droopy upper eyelid, can sometimes be compensated for by the individual raising their chin or forehead, which in turn causes the upper eyelid to retract slightly, exposing the upper sclera. Conversely, conditions like facial nerve paralysis, such as Bell’s Palsy, can reduce the tone of the lower eyelid muscle, causing it to sag and expose the lower sclera, mimicking Yin Sanpaku. Trauma or surgical changes that impact the delicate musculature or nerve supply around the orbit may also alter the resting position of the eyelids, leading to a visible Sanpaku presentation.
Separating Fact from Folklore
Public interest in Sanpaku eyes stems from historical and cultural interpretations, particularly traditional Japanese and Chinese face reading, known as physiognomy. In these systems, the appearance was associated with a lack of balance within the individual’s physical or mental state. Yin Sanpaku was sometimes linked to internal imbalances, while Yang Sanpaku was linked to external threats or dangers.
These traditional associations led to claims that the eye structure could predict personality flaws, misfortune, or impending health crises. However, these ideas are rooted in folklore and superstition and have no basis in modern medical or scientific understanding. Biologically, the Sanpaku appearance is either a harmless anatomical quirk or a visible symptom of an underlying medical condition.