It is generally accepted that Korean eye looks smaller than Western eye and double-folded eye looks bigger than single-folded eye. The upper eyelid covers 1 to 2 mm of the cornea in Caucasians, but few study of the criteria of Koreans has been described. Therefore, so far, the criteria of Caucasian eyelid has been used for the treatment of blepharoptosis. And, there has been no literature about the reason why double-folded eye looks bigger than single eye.
 The purpose of this study is to determine the normal upper eyelid covering-level of limbus of cornea, the width and height of palpabral fissure, diameter of the cornea and MRDI(Margin Reflex Distance 1), measured from 202 Korean adults in their twenties. 

 The results are as follows: 
1) The width of palpabral fissure is 29.1±1.1mm and the heigth is 7.8±1.2mm. 
2) The horizontal diameter of cornea is 11.9±0.4mm and the vertical si 11.2±0.4mm 
3) The corneal coverage of upper eyelid is 3.1±0.9mm and that of lower lid is 0.3±0.5mm 
 In group with double fold, upper eyelids cover 2.7±0.9mm of the cornea. In group that has single eyelid without pseudoblepharoptosis, lids cover 3.2±0.7mm. In group with pseudoblepharoptotic singe eyelid, those cover 4.0±0.9mm. 
4) The MRD1 is 2.4±1.0mm
 In conclusion, the value of corneal coverage by upper eyelid among Koreans is 3.1mm, Which is significantly different form 1 to 2mm of Caucasians. So, we must correct the criteria of diagnosis and operation on blepharoptosis among Koreans. The upper lid covers the cornea in single eyelid more than double eyelid and the double fold operation may increase actual palpabral fissure height.