There are medical terms for single eyelids and heavy eyelids, with single eyelids being the colloquial term for a single eyelid and heavy eyelids being the natural double eyelids. Unilidirectional and blepharoplasty are the more standard medical terms for the presence or absence of a natural fold in the upper eyelid area. The difference between single and heavy eyelids is the effect on appearance. Some heavy eyelids allow more eyelashes to be upturned and the cornea of the eye to be more exposed, giving a potentially more spiritual appearance. Nowadays, there are many people seeking double eyelid surgery, mainly to improve their appearance.