Published 13 November 2026 · Reviewed by Dr Sin Yong
A double eyelid has a visible crease above the lashes. A single eyelid, or monolid, has none. The difference is anatomical: it depends on whether fibres of the muscle that lifts the lid reach the skin, and on how low the fat inside the lid sits.
Short answerA double eyelid has a crease because fibres from the lifting muscle of the lid attach to the skin and pull it in when the eye opens. In a single eyelid, or monolid, those attachments are fewer and the fat inside the lid sits lower, so no crease forms. Both are normal anatomy. A crease can be created only by surgery. Dr Sin Yong assesses lids on Orchard Road, Singapore, treats hooding from lax skin or a low brow without surgery, and refers where surgery is the right route.
The upper lid is lifted by a muscle called the levator. Its flat tendon, the levator aponeurosis, fans out as it reaches the lid. In a double eyelid, the aponeurosis joins the orbital septum at or above the top edge of the firm plate inside the lid, and its fibres attach to the muscle and skin in front. When the eye opens, those fibres pull the skin in and a crease appears (American Academy of Ophthalmology EyeWiki).
In a single eyelid, that junction sits lower and fewer fibres reach the skin. The fat that lies in front of the aponeurosis also sits lower, and is thought to get in the way of those attachments. An anatomical study comparing Asian and Caucasian upper lids described these differences (Jeong 1999).
Single eyelid vs double eyelid, side by side
Swipe sideways to see the whole table.
Lines that appear with smiling are from muscle movement. Illustrative image, not a patient.
Single eyelid (monolid)
Double eyelid
Crease
None, or very low and hidden
Visible above the lashes
Fibres from the lifting muscle to the skin
Fewer
Present; they pull the skin in as the eye opens
Where the aponeurosis meets the septum
Lower, below the top edge of the tarsal plate
At or above the top edge of the tarsal plate
Fat inside the lid
Sits lower
Sits higher
Function of the eye
Normal
Normal
There are in-between forms too: a low crease, a crease that tapers towards the nose, more than one fold, or a fold that comes and goes with swelling or tiredness.
How common is each?
Reported figures vary widely with the population studied. Summaries of the literature give a double eyelid in roughly 24 to 45 per cent of Koreans, 67 to 83 per cent of Chinese and about 82 per cent of Japanese (American Academy of Ophthalmology EyeWiki). Single and double eyelids both occur across ethnic groups, which is why some authors prefer to speak of a low or a high crease.
Can a single eyelid become a double eyelid?
It can change on its own. With age, loss of fat and thinning skin, a crease sometimes appears where there was none, or a crease that was there becomes hidden under loosening skin.
Tape and glue hold the skin in a fold for the day and wash off. They do not change the anatomy.
Surgery is what creates a lasting crease. In the suture method, stitches are buried to join the skin to the deeper layer. In the incisional method, a cut is made, tissue may be removed, and the skin is fixed to the aponeurosis. Risks described for both include asymmetry, a crease in the wrong place, difficulty closing the eye, a drooping lid and bleeding; the suture method can loosen with time, and the incisional method leaves a scar (American Academy of Ophthalmology EyeWiki).
A single eyelid is how the lid was built. A lid that has become heavier over the years is a different matter, with three usual causes: loosened lid skin, a brow that has come down, or a weakened lifting muscle, which is called ptosis. These are explained on droopy and hooded eyelids.
A lid that droops suddenly, on one side, or with double vision or a change in pupil size needs a doctor the same day.
How Dr Sin Yong assesses the upper lid
Crease or no crease. Whether a crease exists, how high it sits and whether skin now covers it.
Skin, brow or muscle. Which of the three is making the lid look heavy.
What can be treated without surgery. Lax or finely wrinkled lid skin with the FSX Laser, and a brow that has dropped with the VF Periorbital Eyelift, as set out on non-surgical eyelid lift.
What is referred. Creating a crease, a weak lifting muscle and marked excess skin are surgical, and are referred to a specialist who performs eyelid surgery.
Your next step
1. MessageWhatsApp the clinic with what is bothering you. A reply comes from the clinic, not a bot.
2. AssessmentDr Sin Yong examines you himself on Orchard Road, Singapore.
3. A plan in writingWhat he would do, what he would not, the fee factors, and the option of no treatment.
Every treatment is performed by Dr Sin Yong personally. Singapore Medical Council registered · invited to share his clinical expertise internationally for CLASSYS, DEKA, Fotona, Hironic and Ilooda.
The lid, the brow and the skin are examined before any plan is made. How consultations work.
A double eyelid has a visible crease above the lashes; a single eyelid, or monolid, does not. The crease forms where fibres from the muscle that lifts the lid attach to the skin. In a single eyelid those attachments are fewer and the fat inside the lid sits lower.
Yes. Monolid is the everyday word for a single eyelid, an upper lid with no visible crease.
Sometimes. With age, as fat inside the lid reduces and the skin thins, a crease can appear. It can also come and go with swelling or tiredness.
No. Lasers, radiofrequency and ultrasound can tighten lid skin or lift the brow, but they do not create a crease. A lasting crease is created by surgery.
No. It is normal anatomy and the eye works normally. A lid that droops and covers part of the pupil is a different condition, called ptosis, and should be examined.
No. Tape and glue hold the skin in a fold while they are on. They do not change the attachments inside the lid.
References
Jeong S, Lemke BN, Dortzbach RK, Park YG, Kang HK. The Asian Upper Eyelid: An Anatomical Study With Comparison to the Caucasian Eyelid. Archives of Ophthalmology, 1999. source
American Academy of Ophthalmology. Single Fold/Double Fold Lid Surgery. EyeWiki, accessed 2026. source
About this page: written and medically reviewed by Dr Sin Yong, MBBS (NUS), MRCS (Edinburgh) · Last reviewed 13 November 2026 · Illustrative images only, not patients · Editorial policy
