There was, and there still is a huge audience of girls who want to fix their monolid eyes to double eyelid ones without going through expensive plastic surgery operation called double eyelid surgery
In 1970’s the Japanese people invented eyelid glue, often heard called as “eye putti” (アイプチin Japanese which is pronounced like “ai puchi”)
There is also variant called double eyelid tape for those who do not want to mess up with the glue.
Anyway, the main function in these 2 is exactly the same – to give an impression of having a double eyelids.
Double eyelid glue is painted on the upper eyelid which is then pushed upwards with a plastic prong. It will then be held in place for a minute to let the glue dry, archiving a good hold.
Glue has its downsides: it does not hold up for more than few hours and then it must be reapplied. It might cause irritation and it takes quite a lot of practice to master using it.
But in other hand, the glue gives more natural look compared to the tape hence its ability of being invisible and it is not thick like the tape is.
Double eyelid tape is fibrous elastic strip which are either cut into the shape to fit the eye or the user needs to do the cutting and trimming by themselves. Double eyelid tape is then placed on the eyelid and it works just like the glue but the tape should be much stronger and hold up the desired look for longer. It is also a bit faster to apply compared to the glue. People looking for the tape should always buy only the tape with medical grade to avoid irritation and nasty infections.
There is also a thing called double eyelid fiber available. Fiber should combine best of both worlds of glue and tape – it is quite invisible and it has a strong hold just like the tape has. For first timers it might be a bit hard to use, but well, practice makes perfect.
These products giving a double eyelid are really popular especially among Japanese and Korean teenagers. Not only females, but even some Asian men are using these methods.
Some western people like to use these methods too, but for a bit different reasons. Main reason for their usage is to balance the uneven eyes.
Here is 3 videos showing glue tape and fiber in action: