The most important part of double eyelid surgery is deciding where to set the double eyelid fold. That being how high the double eyelid fold should be. Another factor is the actual design of the double eyelid fold shape.
Every eye is different and among the right and left eyes, they two are different. One of the main cause of eyelid and eye shape asymmetry is due to bony asymmetry.
When the frontal bone growth is significant, the eyeball protrudes and the lateral canthus is positioned higher than the medial canthus. Therefore, there is a slight palpebral fissure slant. When there is a difference in eyeball protrusion or slant between the two eyes but the double eyelid fold is made symmetrically, then postoperative asymmetrical double eyelid fold will occur. In the eye that has a high lateral canthal tilt, the lateral fold region height should be parallel to the central region fold height. On the contrary, in the eye that does not have the high lateral canthal tilt, the lateral double eyelid fold region height should be higher than the central region double eyelid fold height. When these fine and subtle adjustments are made, then the postoperative result of the double eye fold height and the overall eye appearance will look more similar to each other.