Chen's Double Eyelid Fold Illusion: An Eye Size Assimilation Illusion Induced by a Supratarsal Fold in the Brow-Eye Unit, A Preliminary Report.

[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.

[LEVEL OF EVIDENCE IV] This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to Table of Contents or the online Instructions to Authors www.springer.com/00266 .