Background: Double eyelidplasty can enhance the eye size and facial attractiveness of Asian individuals with single eyelids. The authors hypothesize that a supratarsal fold can induce an eye size assimilation illusion to enhance eye dimensions and aesthetics, and seek to define the optimum vertical proportion between a supratarsal fold and the eye fissure associated with maximal induction of the size assimilation illusion.
Methods: A photometric study of the replicated photographs of ten female Taiwanese patients after double eyelidplasty was designed. Each photograph was edited by shifting the supratarsal folds vertically at a regular fold/eye ratio increment of 0.1. The perceived attractiveness of edited photographs of each patient was rated by 100 adult observers using a score of 1-5. The palpebral parameters were measured and analyzed.
Results: The mean rating score increased gradually when a supratarsal fold was added and peaked when the fold/eye ratio was 0.3 and the mean Chen's double eyelid fold ratio was 0.631 ± 0.023. After the peak, the mean score decreased gradually and was lower than the photograph without a fold when the fold/eye ratio exceeded 0.5 and the mean Chen's ratio exceeded 0.729 ± 0.027.
Conclusion: Within the optimal ranges of the fold/eye ratio and Chen's double eyelid fold ratio, eyes are perceived as larger and more attractive due to a hybrid presentation of two interdependent eye size assimilation illusions induced by a supratarsal fold in the brow-eye unit. "Chen's double eyelid fold illusion" is proposed to describe this complex visual phenomenon.
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Keywords: Chen’s double eyelid fold illusion; Chen’s double eyelid fold ratio; Delboeuf illusion; Double eyelid; Double eyelid blepharoplasty; Double eyelidplasty.