I've noticed on a number of eyelids among asians wherein the eyelashes seem more prominent following eyelid surgery, and it seems like among some of them, the upper eyelids are covering the eyelashes. Is this something intrinsic to asian eyelids (I don't see it among all of them, though. I've seen alot with single eyelids and eyelid edges that show just fine.) or some other genetic trait?
Anatomy of Asian Eyelids
Doctor Answers 6
Eyelashes Move Up When a Crease is Made
You have made a good observation in that a person without double eyelids will have eyelashes that are aiming down. Also, not only would the eyelashes be aiming down, but if there is excess upper eyelid skin pushing down against the eyelashes, then it can also cause irritation to the cornea or irritation in sensation. However, by having a double eyelid surgery the eyelashes move up. One can think of the mechanism as a blanket that is just hanging versus somebody pushing that blanket in. Then what happens is that the bottom part of the blanket would elevate in height but still would want to touch the ground due to gravity. Just like this, when a crease is made on the eyelid, the eyelashes that are aiming down move up about 90 degrees. This is just a pure physical mechanism of a surface area that is being pushed in a concave manner.
Eyelashes are uncovered by surgery
Your observation about the change in eyelid length has to do with their relative length. In before and after photos where the eyelashes appear to grow longer, the change is actually due to the fact that the extra skin pushing against and hiding a part of the eyelashes is either pulled upwards or removed during the course of double eyelid surgery. This allows you to see the full length of the eyelashes, and so they appear much longer.
Eyelashes ARE more noticable after double eyelid surgery
Often, the skin of a single (fold) eyelid overhangs the eyelashes, thus making them appear shorter. With double eyelid surgery, the excess skin overhanging the eyelash is either pushed into the new crease and/or removed so much more of the eyelashes can be seen, thus making them appear longer. (Also, you will get less mascara smudges onto your eyelid skin since the skin will not be overhanging and pressing onto the eyelashes).
The amount of excess "skin" covering the eyelashes will depend on each person's anatomy, such as the quanitity of orbital fat, height of levator insertion onto overlying skin, etc.
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The upper eyelashes will evert after Double fold surgery
The unique anatomy of the asian single fold lid does affect the eyelash orientation .The lashes of these patients may tend to be aimed downwards or sometimes even towards the eyeball. When double fold surgery is performed, the lashes tend to 'unfurl' and evert. This leads to the change in appearance that you have observed.
As for the genetics behind this observation, it appears directly related the presence of single fold lids. The genetics of asian eyelids is not entirely understood. It appears that double folds are 'dominant' with mixed race asian/caucasian children. However, this does not always hold true with asian children born to asian parents when at least one parent has double folds.
Eyelashes can be affected by asian eyelid skin
Eyelashes can be affected by asian eyelid skin. When you lack a double eyelid crease, the extra skin can lay over the eyelashes and can affect the way they are positioned. When you do a double eyelid crease procedure, the skin can be positioned higher and this can allow the eyelashes to rise up higher. Also there are ways to attach the levator muscle to the skin and orbicularis muscle to elevate the eyelashes to a different degree with Asian double eyelid surgery / eyelid crease formation surgery. Sometimes this relation of the eyelashes with the eyelid is natural depending on the person's anatomy and what they inherited.
Asian eye lid
I am not sure you can make a blanket statement on the external look or as you say anatomy of the asian eye lid.
The internal anatomy is well known. External look, you should allow for individual variation as in any other racial attributes.