There are many reasons to affect the height and depth of double eyelids.
Eyelids are a dynamic 3D structure. Once the double eyelid folds of the same shape are placed in the sockets of different depths, different levator muscles and different eye widths, even if they are the same double eyelid folds as eyes close, they are not symmetrical as eyes open.
When the depths of both eye sockets, eye positions and levator muscle functions are different, but you still want to have the same double eyelids when opening eyes, then doctors can only draw different lines on respective eyes so that you can have identical eyes when opening them.
So sometimes in a bid to be symmetrical when opening eyes, doctors will draw different lines when the eyes are closed.
Some have droopy outer eye corners, some have sockets of different depths, and still some have different amount of fat on each eye and Mongolian folds of different degrees, and so in double eyelid surgery, even the convex of both brow bones should be considered. Therefore, it’s not like drawing the same lines on both closing eyes, and they will be the same when eyes open. Every factor must be considered to get a symmetrical result as eyes open. Detailed evaluation and complete planning by an experienced doctor before the surgery can help achieve satisfactory results more.