What are Monolids?

Monolids, also known as single eyelids, are an eye shape in which the upper eyelid doesn’t have a visible crease, and there is a smooth, single fold of skin from the brow to the eyelashes.

In addition to an absent upper eyelid crease, monolid eyes often have an epicanthic fold. Sometimes called an epicanthal fold, this skin fold of the upper eyelid covers the inner corner of the eye, medically known as the medial canthus.

While monolids are most prevalent in people of Asian descent, they can occur in people of any ethnicity.

Having monolid eyes is not inherently harmful or dangerous. However, some people wish to create or emphasise the crease in their upper eyelid for a number of reasons:

• Aesthetic preferences
• Facial balance
• Functional concerns

Cadogan Clinic has brought together a team of specialist Consultant Eye Surgeons who are all experts in their field. In 2025, over 1 in 10 of the procedures our surgeons performed included Blepharoplasty.

What Are the Symptoms of Monolid Eyes?

There are several signs and features which characterise monolid eyes and epicanthal folds:

• Smaller eye appearance - Reduced distance between the upper and lower eyelids can make the eyes appear smaller
• Flatter eye appearance – The lack of upper eyelid crease gives the eye area less definition and dimension
• False crossed eyes (pseudoesotropia) – Although the eyes are aligned correctly, they may appear closer together or crossed due to the inner corners being covered
• Swollen eyelids – Excess ocular subcutaneous fat and tissue can cause the eyes to look swollen or puffy

For the majority of individuals, mono eyelids and epicanthic folds are harmless and pose no medical concern. However, in some severe cases, they may cause functional concerns which require treatment:

• Obscured vision – Although extremely rare, pronounced epicanthal folds can limit the field of vision
• Eyelid skin tension – Severe epicanthal eye folds can result in extra tension being placed on the upper eyelid and eyelashes, causing discomfort

The signs associated with monolids vary between individuals. While some people may find they aren’t affected, others may have significant symptoms which require intervention.

What Causes Monolid Eyes?

Monolid eyes primarily occur as a result of genetics. However, there are several variations in these causes, which it is important to understand:

Ethnicity

Monolids and epicanthal folds are common physical characteristics found in many ethnic groups. Although they are most often associated with people of Asian descent and appear in around 50% of people with an Asian background, they also often occur in populations including:

• Indigenous Americans
• Polynesians and Micronesians
• Sámi, an indigenous Arctic group
• Khoisan group in Southern Africa
• Nilotic group in Central Eastern Africa

Several theories have been proposed to explain why monolids and epicanthic folds developed in these communities, including as an adaptation to certain climates and environments. However, these theories have never been fully proven, and the exact reason remains unclear.

Although monolids and epicanthic folds are especially common in people of these ethnic groups, they can occur in people of any ethnic descent.

Genetic Conditions

Monolids and epicanthal folds are commonly seen in several genetic conditions. This is typically due to abnormalities in genes or chromosomes that disrupt normal facial development.

It is important to remember that the presence of monolids or epicanthal folds does not indicate a genetic condition. For individuals with a genetic condition, monolids and epicanthal folds are still not harmful or dangerous.

Genetic conditions which are often associated with monolids and epicanthal folds include:

• Down’s Syndrome – An extra chromosome causes specific physical traits and developmental delays
• Turner Syndrome – Only affecting females, a missing X chromosome results in reduced height and developmental delays
• Williams Syndrome – A missing portion of chromosome 7 causes certain facial features, developmental delays and learning difficulties
• Noonan Syndrome – Certain gene mutations cause distinct facial characteristics and heart concerns
• Triple X Syndrome – Only affects females and is caused by an additional X chromosome
• Zellweger Syndrome – A genetic mutation severely affects the nervous system and metabolism
• Rubinstein-Taybi Syndrome – Caused by a genetic mutation, resulting in enlarged toes and thumbs, reduced height, and learning difficulties
• Blepharophimosis Syndrome – A genetic mutation which affects eyelid development, resulting in narrow eye openings and drooping eyelids.

Genetic conditions are usually identified soon after birth or in early childhood. Although eye shape may be considered when testing and diagnosing these conditions, medical professionals will look for a wide range of signs and symptoms.

Foetal Alcohol Syndrome

Foetal Alcohol Syndrome (FAS) is a permanent condition which affects physical and mental development, caused by drinking alcohol during pregnancy.
The signs and symptoms of Foetal Alcohol Syndrome vary between individuals, but can include:

• Distinct facial features, including small eyes with monolids, epicanthal folds, and a smooth ridge between the nose and upper lip
• Reduced height and weight
• Vision and hearing problems
• Developmental delays and learning difficulties
• Poor coordination
• Hyperactivity and difficulty concentrating

Foetal Alcohol Syndrome occurs because when consumed, alcohol passes through the mother’s bloodstream to the foetus through the umbilical cord. 

The baby cannot process alcohol properly, and it stays in their system for a longer period of time. This leads to cell death and abnormal development, particularly in the central nervous system.

Additionally, alcohol constricts blood vessels, reducing blood flow to the placenta, and preventing sufficient oxygen and nutrients from reaching the foetus.

It is important to remember that the presence of mono eyelids and epicanthal folds does not inherently indicate that someone has Foetal Alcohol Syndrome.

Why Do People Want to Adjust Monolid Eyes?

Bearing in mind that, for most people, monolid eyes and epicanthal folds are not harmful and, in most cases, do not cause functional concerns, it may not be obvious why people wish to address or change their eye shape.

There are several reasons people wish to adjust their monolids:

Aesthetic Preferences

For many people, the motivation to change the shape of their monolid eyes is aesthetic.

Although it is often assumed that this is caused by a desire to appear more in line with Western beauty standards, this is often not the case.

Aesthetic reasons that people want to change their eye shape include:

• Achieving larger eyes
• Making the eyes look more open
• Enhancing expression
• Improving the definition of the eye area
• Reducing excess tissue to address the appearance of puffiness or under-eye bags

Procedures to address aesthetic concerns related to monolid eyes often aim to preserve the overall impression of the eyes while enhancing their shape and expression.

Facial Balance

There are several ways the appearance of monolid eyes may affect facial balance and proportions.

• Asymmetry – Many people find that they have a monolid or epicanthal fold on one side, but not the other, or that they have slightly more crease definition in one eye, due to slight differences in muscle strength and connection
• Small eyes – Small eyes may appear disproportionate or imbalanced to other facial features
• False crossed eyes – In cases where the eyes look misaligned due to monolids or epicanthic folds, it can affect the balance of the face
• Disproportionately drawing attention – Individuals with severe epicanthic eye folds may feel that the feature draws more attention than they would like

Defining the upper eyelid crease and reducing epicanthal folds can create a more balanced, proportionate overall facial appearance.

Functional Concerns

Although functional concerns caused by monolids and epicanthal folds are relatively rare, they are often among the reasons people seek to adjust the shape of their monolid eyes.

Functional concerns in monolids usually arise as reduced vision, or eyelid strain and tension.

In monolids, typically, the field of vision can be reduced because:

• An increase in skin laxity under the brow bone causes loose skin to hang over the upper eyelid, obscuring vision
• In rare cases, an epicanthal fold may be significant enough to block vision

Reduced vision can significantly impact the ability to carry out daily activities, confidence and independence.

Eyelid tension in monolids is caused by the upper eyelid naturally resting against the lash line, which puts pressure on the eye area. In double eyelids, the natural crease provides extra support, reducing pressure on the upper eye; however, monolids lack this structure, allowing the skin to push down on the eyelashes.

Over time, this pressure can cause tension on the eyes, increasing eye strain and fatigue, impacting comfort and quality of life.

If you are concerned about reduced vision or eye strain caused by monolids or epicanthic folds, it is important to speak with an experienced Consultant Eye Surgeon to prevent these concerns from worsening.

Words From Our Founder