Defining Ideal Double Eyelids With a Morphometric Analysis in Asians

Abstract

Background

Double eyelids are always considered crucial aesthetic symbols. Despite numerous studies conducted on the attractiveness of double eyelids, there remains a dearth of research on quantitative and morphological evaluation of ideal double eyelids.

Objectives

In this we study aimed to investigate the optimal height and morphological characteristics of ideal double eyelids.

Methods

Participants were presented with a total of 9 images, consisting of 1 single eyelid image and 8 double eyelid images, featuring 2 distinct shapes and 4 varied pretarsal shows. Respondents were instructed to assign scores ranging from 1 (least attractive) to 5 (most attractive) for each image. Subsequently, the scores for each image were analyzed based on population demographics, followed by the calculation of aesthetic metrics.

Results

The whole cohort deemed images with a 2-mm fold to be more attractive than 1 mm (P < .001), followed by 3 mm and 0 mm (single eyelid), and finally, 4 mm. Morphologically, significant differences were found between images with the same pretarsal shows of 3 mm (P < .001) and 4 mm (P = .026). Most subgroup analysis results were aligned with those of the cohort, with gender being the most significant factor in distinguishing double eyelid aesthetics. Additionally, aesthetic characteristics of 2-mm folds were found to be comparable to appealing double eyelids in previous studies.

Conclusions

In this study we validated the optimal heights and morphology of double eyelids, thereby addressing the existing gap in aesthetic studies on double eyelids. These findings hold significant implications for surgical planning, effect assessment, and other periocular procedures related to upper blepharoplasty.

Level of Evidence: 4

The double eyelid has long been an important facial aesthetic symbol, and the demand for blepharoplasty in Asia is substantial.¹ Previously, this desire was sometimes attributed to patients pursuing a more Western appearance. However, it should be noted that the double eyelid is also a distinctive characteristic feature among many Asians.^2,3 Both Western individuals and Asians hold similar perceptions of ideal upper lid proportions, that is, medium-width double eyelids are considered to be the most attractive.^4-6

Several studies have been conducted to summarize the aesthetic characteristics of double eyelids.^7-12 Hwang et al conducted a questionnaire survey and found that medium-height double eyelids were more preferred.⁴ Subsequently, researchers have further refined the specific attributes of attractive double eyelids through their studies. Chen et al, utilizing both questionnaire surveys and picture ratings, discovered that the vertical proportion of the lower subunit (eye plus fold) to the whole brow-eye unit at the fold peak (referred to as Chen's ratio) was 0.631 ± 0.023, with a fold/eye ratio of 0.3:1 observed in the most attractive eyes.¹³ Additionally, Patel et al analyzed numerous images and proposed that Asians perceived beautiful eyes to possess certain characteristics, such as a greater palpebral aperture height to upper lid show ratio and a more lateral brow peak.¹⁴ However, most existing assessment of double eyelids has focused on proportional calculation and qualitative analysis rather than quantitative evaluations. Alghoul et al proposed that double eyelids higher than 4 mm were considered less attractive, but this only represents perceptions of Western reviewers.⁶ The formula proposed by Barmettler et al is considered capable of predicting the postoperative height of double eyelids, making quantitative research on the aesthetically pleasing fold height more feasible, because when we determine the most attractive fold heights that formula will enable us to achieve them during the operation.¹⁵ Furthermore, the aesthetic evaluation of double eyelid morphology has previously been overlooked; however, with the implementation of Suo et al's double eyelid design method, which provides detailed instructions on achieving accurate construction of in-fold or out-fold double eyelids, the study of morphology has become more meaningful.¹⁶

In this paper, 2 types of double eyelid shape were included for morphological study: in-fold (in which the height of the medial crease is lower than the height of the central crease), and out-fold (in which the height of the central crease is similar to the height of the medial crease) (Figure 1A-B). Each type corresponds to 4 different pretarsal shows. Our aim was to investigate through a questionnaire which combination of height and shape resulted in the most aesthetically pleasing double eyelids, and to subsequently analyze the aesthetic characteristics.

METHODS

Participants

A total of 441 individuals voluntarily participated in the study by completing digital questionnaires published on Peking Union Medical College Hospital (PUMCH) social media platforms and WeChat promotions of all authors between February 2023 and June 2023. All respondents were anonymously asked to provide their age, gender, occupation, makeup routine, and previous history of double eyelid surgery. The occupational survey focused on whether the participant was a specialist in the field, such as a plastic surgeon, maxillofacial surgeon, beauty industry practitioner, makeup artist, or other related industry professional. The respondents in this study were exclusively from the People's Republic of China, ensuring that potential ethnic and geographical variations were not considered. The research protocol was approved by the Institutional Review Board of the Peking Union Medical College Hospital (reference no. K2502) and adhered to the principles outlined in the Declaration of Helsinki, with the model providing informed consent for the use and modification of her photograph.

Stimulus Material Creation

An image was collected from a young woman who accepted blepharoplasty to achieve in-fold double eyelids. She did not have any other periorbital surgery history and provided written informed consent. The model was instructed to convey a natural facial expression and hold neutral tilt to ensure accurate cornea position during the photographic shoot.¹⁷ Based on the actual measurement of corneal width of 11.0 mm, images with varying morphology and pretarsal shows were generated with Photoshop CC 2020 (Adobe Systems, Inc., San Jose, CA) tools. Initially, the original in-fold upper eyelid crease was vertically adjusted to target heights at intervals of 1 mm, resulting in 4 images (Figure 2A-D, corresponding to upper eyelid crease heights of 1, 2, 3, and 4 mm). Subsequently, the double eyelid folds between the inner canthus and punctum in each image were individually modified respectively, and 4 images of the out-fold double eyelid crease with different heights were obtained (Figure 3A-D, corresponding to upper eyelid crease heights of 1, 2, 3, and 4 mm). Finally, the image lacking an upper eyelid crease was generated by utilizing the lasso tool and patch tool to substitute the upper eyelid folds with adjacent skin texture (Figure 4, single eyelid). Several additional Photoshop techniques were employed to enhance the natural appearance of the images. Consequently, a total of 9 images were produced for inclusion in the questionnaire.

Study Design

The study comprised 2 components: the administration of a questionnaire and the measurement of aesthetic metrics. The questionnaire encompassed demographics and the morphed images. After anonymously providing baseline information, participants were presented with 9 distinct images and instructed to rate each image's attractiveness on a scale from 1 (least attractive) to 5 (most attractive), to determine the most desirable height and shape for double eyelids. The images were presented in a random order and respondents were reminded to focus on the double eyelids. The subsequent analysis of scores involved the cohort analysis and subgroup analysis based on demographic factors, including age, gender, occupation, makeup routine, and experience with upper blepharoplasty. Then, all images were analyzed with Image J (National Institutes of Health, Bethesda, MD). Three linear distances at the midpupillary line were measured, and 2 related linear distances and 3 ratios were calculated to define the aesthetic characteristics of double eyelids (Table 1, Figure 1A-B).

Statistics Analysis

The ratios were calculated with software Microsoft Excel 2019 (Microsoft Corp., Redmond, WA), while other statistical analysis of the data was conducted with SPSS version 25 software (IBM Corp., Armonk, NY). The scores were expressed with means and standard deviations. Normality analysis was performed with the Kolmogorov-Smirnov test, while the Mann-Whitney U test was utilized to compare variables between different groups. A P value of <.05 was considered statistically significant in cohort analysis, and a P value of <.01 was considered statistically significant in subgroup data analysis.

RESULTS

Demographics

The questionnaire was voluntarily completed by a total of 441 individuals, for whom demographic information is presented in Table 2. The mean age of the whole cohort was 35.5 years (age range, 17-64 years), including 89 males (20.18%) with a mean age of 38.2 years (age range, 17-64 years) and 352 females (79.82%) with a mean age of 34.8 years (age range, 17-61 years). Among the whole cohort, 272 individuals were aged 40 years or below, while 169 respondents belonged to the age group above 40 years. Despite nonmedical respondents being nearly 4 times more likely than specialists to respond (356, 80.73% for nonspecialists vs 85, 19.27% for specialists), there were no significant differences in age between the 2 groups (35.9 years, ranging from 21 to 64 years vs 33.8 years, ranging from 17 to 59 years). The proportion of participants with a makeup habit accounted for approximately half (232, 52.61%). Additionally, almost half of the participants had undergone double eyelid surgery (203 individuals, accounting for 46.03%).

Total Cohort Scores

The scores for each image are displayed in Figure 5, while the P values for comparing every pair of images are presented in Table 3. The highest mean scores were obtained for images with a pretarsal show of 2 mm in both the in-fold (3.72) and out-fold (3.65) types of double eyelids, followed by images with pretarsal shows of 1, 3, and 0 mm (absent of upper eyelid crease); the least attractive upper eyelid height was 4 mm. First, the score of the single-eyelid image was pairwise compared with the scores of the other 8 images, revealing significant differences in all pairs except for the comparison between the single eyelid and out-folded double eyelid measuring 3 mm (P = .533). However, this did not impact the finding that 2-mm double eyelids were considered most attractive across both shape types (P < .001). The P value was then calculated among the double eyelid heights, revealing a significant disparity in scores between each pair of images within the same shape group (P < .001).

The scores for in-fold creases were consistently higher than those for out-fold creases at each height. By comparing the scores of images with double eyelids of the same height but different shapes, we observed no statistically significant difference between the 2 morphology groups with identical upper eyelid heights of 1 and 2 mm. However, the attractiveness of double eyelid crease heights measuring 3 and 4 mm exhibited a significant association with morphology (P < .001 for 3-mm upper eyelid creases and P = .026 for 4-mm upper eyelid creases).

Subgroup Score Analysis

The ranking of attractiveness for different heights of double eyelids and the preference for the in-fold double eyelid shape were consistent with that of the overall cohort in each subgroup; however, the results for each subgroup also exhibited distinct characteristics.

Male vs Female

The scores of respondents of different genders are shown in Supplemental Figure 1, available online at www.aestheticsurgeryjournal.com. Both genders rated the 2-mm-high crease as the most attractive in both morphology groups (male, 3.7 for in-fold and 3.85 for out-fold; female, 3.73 for in-fold and 3.6 for out-fold) with no significant difference observed between them. However, gender-based differences were observed in images featuring upper eyelids with heights of 1, 3, and 4 mm, regardless of shape. Females exhibited significantly less interest in upper eyelid creases measuring 1, 3 and 4 mm compared to males regardless of the shape, which likely contributed to the statistically lower scores given by the entire cohort to images displaying these heights' pretarsal shows, considering the substantial number of female respondents.

Respondents Older Than 40 Years vs Respondents 40 Years or Younger

The results of different age groups are presented in Supplemental Figure 2, available online at www.aestheticsurgeryjournal.com. In the age subgroup analysis, the 2-mm-high crease was also deemed the most appealing for the 2 different shapes (≤40 years, 3.71 for in-fold and 3.64 for out-fold; >40 years, 3.73 for in-fold and 3.73 for out-fold). No significant difference was observed in the scores assigned to 5 images (2 images with a fold height of 2 mm, 2 images with a fold height of 1 mm, and 1 image with no double eyelids) between the 2 age groups. In contrast, the comparison between images with pretarsal shows of 3 and 4 mm yielded statistically significant differences in both age groups, and it was observed that older individuals exhibited a higher degree of tolerance toward higher double eyelids.

Specialist vs Nonmedical Respondents

The scores of specialists and nonmedical respondents are displayed in Supplemental Figure 3, available online at www.aestheticsurgeryjournal.com. The 2-mm-high crease was deemed most attractive with different shapes in both subgroups, with no significant difference. It is worth emphasizing that there was a higher degree of homogeneity observed between specialists and nonmedical respondents than initially anticipated, with only 3 images displaying statistically significant differences in ratings. Notably, it was discerned that professionals assigned notably lower scores for more pronounced upper eyelid creases (in-fold 3 mm, out-fold 3 mm, and out-fold 4 mm), potentially reflecting the preferences of the majority of patients seeking double eyelid surgery whom they encounter.

Participants With Makeup Routine vs Participants Without Makeup Routine

The results related to makeup routine of respondents are shown in Supplemental Figure 4, available online at www.aestheticsurgeryjournal.com. Double eyelids with a 2-mm height were agreed to be the most attractive by both subgroups, and it was observed that makeup habits had minimal impact on the aesthetics of double eyelids, as evidenced by significant differences in ratings only for 3 images (in-fold 1 mm, in-fold 4 mm, and out-fold 4 mm).

Participants With or Without Experience of Blepharoplasty

The results are presented in Supplemental Figure 5, available online at www.aestheticsurgeryjournal.com. When the results were analyzed by subgroup based on the experience of blepharoplasty, both subgroups considered a 2-mm eyelid height as the most attractive regardless of shape (with, 3.81 for in-fold and 3.61 for out-fold; without, 3.65 for in-fold and 3.69 for out-fold). The respondents without previous blepharoplasty exhibited higher scores for all 9 images, with statistically significant differences observed in 5 of them (in-fold 3 mm, in-fold 4 mm, out-fold 1 mm, out-fold 3 mm, and out-fold 4 mm), compared to respondents who had had previous blepharoplasty. Similarly, the statistical significance was primarily concentrated in scores of images with higher pretarsal shows.

Aesthetic Characteristic Measurements of Double Eyelids

Three linear distances were measured, from which 2 linear indices and 3 ratios were calculated (Figure 1A-B, Table 1). The results are presented in Table 4. The palpebral aperture height and the brow-eye unit height were consistent across all images (aperture height: 11.072 mm; brow-eye unit height: 20.814 mm). The upper lid show varied based on pretarsal show, while their cumulative value remained constant. Chen's ratio of the image without a fold was 0.532, and it increased proportionally with the augmentation of pretarsal show until it approached the golden ratio of 2 mm (Chen's ratio of 2-mm crease height: 0.630). Interestingly, Chen's ratio with a pretarsal show of 4 mm deviated further from the golden ratio than Chen's ratio without double eyelids (0.724 for 4-mm crease height and 0.532 for single eyelid), which was in line with the image scores. The ratio of the fold to eye and the ratio of palpebral aperture to upper lid show both exhibited an increase with augmentation of pretarsal show, with values of 0.184 and 1.43 corresponding to the most aesthetically pleasing double eyelids.

DISCUSSION

The eye and periorbital structures play a crucial role in nonverbal communication, conveying an individual's emotions and interests, therefore holding significant importance in determining attractiveness.⁴ The presence of a double eyelid, often associated with an ideal upper eyelid, should be emphasized as not exclusive to Caucasians; many Asian individuals also possess this distinctive feature.^2,3 As awareness of its impact on facial beauty has grown, extensive research has been conducted to explore the most appealing characteristics of double eyelids. However, the current research has primarily focused on proportions and qualitative analysis, lacking direct quantitative research and investigations into the morphology of ideal double eyelids. Therefore, we gathered data on the height and shape of the most appealing double eyelid through a questionnaire featuring 9 pictures depicting different shapes and heights of double eyelids. Subsequently, the aesthetic characteristics of double eyelids were analyzed.

Participants demonstrated a high level of consensus in their evaluations of double eyelid aesthetics. The scores for double eyelids measuring 1 to 3 mm were significantly higher than those for single eyelids (P < .001), indicating a consensus on the enhanced beauty associated with double eyelids. In terms of height, both types of 2-mm fold were considered significantly more attractive (P < .001) than other heights, such as 1 mm, followed by 3 mm, 0 mm (single eyelid), and finally 4 mm. The findings suggested that Asians prefer medium double eyelids, consistent with previous studies conducted by Hwang.⁴ Moreover, in a retrospective study conducted by Alghoul et al, it was found that the reviewers' assessment of double eyelid attractiveness in patients with a double eyelid height greater than or equal to 4 mm was significantly lower, indicating that Westerners also consider double eyelids exceeding 4 mm to be aesthetically unpleasing.⁶ However, it is important to note that the scores for the 4-mm upper eyelid crease in our study were lower than those for single eyelids, whereas Hwang et al's results showed the opposite trend, which has 2 potential explanations. First, although in Hwang's study it was concluded that there were no significant racial differences in double eyelid aesthetics based on subgroup analysis, the potential influence of racial aesthetic variations on these findings could not be ruled out. Moreover, this may partially reflect the limitations of qualitative analysis, because it did not surpass the “threshold value” for unattractive high double eyelids, which was 4-mm in our study. Chen et al also proposed that when the ratio of fold to eye exceeded 0.5:1, the score for double eyelids was lower than single eyelids, confirming that when the height of double eyelids surpassed a certain threshold, their attractiveness was not as favorable as that of single eyelids.¹³ Therefore, we recommend avoiding excessively high upper eyelid creases.

This study represents the first direct investigation into ideal double eyelid morphology. By comparing scores assigned to images depicting double eyelids with varying shapes but equal height, we observed that while the in-fold score surpassed the out-fold score in all images, there was no significant distinction between 1- and 2-mm folds; however, a noticeable difference emerged for 3- and 4-mm folds. This suggested that morphology plays a minor role in aesthetics for medium or low upper eyelid creases but exerts greater influence on higher ones. Furthermore, all subgroup analyses showed the same results as the cohort study regarding double eyelid morphology aesthetics. This may be because the slight variation between the 1 forms was primarily observed near the inner canthus, resulting in a less apparent morphological distinction in low or medium folds. However, as the double eyelid widened, this morphological difference gradually became more pronounced. Drawing from Suo et al's study and advancements in surgical technology, we posited that patients should be able to select their preferred shape of double eyelids based on personal preferences.¹⁶

The aesthetic variations in subgroup analysis primarily revolve around the height of the double eyelid. Specifically, young females and individuals with previous blepharoplasty experience or a habitual use of makeup demonstrated lower scores for 3- and 4-mm double eyelids. Moreover, the disparity between these individuals' scored images was more pronounced, indicating their heightened expectations regarding double eyelid height, which was consistent with the characteristics of the population seeking double eyelid surgery. Gender subgroup analysis revealed significant differences in most scores, with females scoring significantly lower than males on images featuring 1-, 3-, and 4-mm folds, indicating that gender is a primary factor influencing the aesthetic of double eyelids. The increased emphasis on double eyelids, as well as the influence of artists, fashion, and other related factors, may have heightened their sensitivity to variations in the height of upper eyelid creases. In contrast, the disparity in aesthetic ratings between specialists and nonmedical respondents was unexpectedly minimal, challenging the notion that a related profession influences aesthetic preferences. Moreover, subgroup analyses revealed minimal significant distinctions among 1-mm folds and no statistically significant differences among 2-mm folds for individuals, indicating a consensus in the aesthetic evaluation of narrow to medium double eyelids.

To investigate the factors contributing to the attractiveness of the 2-mm-high upper eyelid crease, we conducted measurements of 9 images, specifically focusing on 3 linear metrics at the midpupillary line (Figure 1A-B, Table 4). Subsequently, 2 linear distances and 3 proportions were calculated (Figure 1A-B, Table 4). Our findings revealed that Chen's ratio for 2-mm folds closely aligned with the ratios of the most attractive double eyelids observed in Chen et al's article (0.630 vs 0.634). As explanation, Chen et al proposed that the aesthetic modification of double eyelids in the eyes is attributable to a size assimilation illusion effect, which means that the presence of double eyelids is perceived as an integral part of the eye, resulting in an enlargement effect on the eyes.^13,18-20 However, an upper eyelid crease higher than 4 mm or with a fold/eye ratio exceeding 0.5:1 was considered less appealing compared to single eyelids. This could be due to difficulties assimilating excessively wide double eyelids as a natural component of the eye, thereby affecting overall brow-eye unit coordination. The pretarsal show, palpebral aperture height/upper lid show ratio, and the fold/eye ratio closely aligned with the findings summarized by Patel et al in Asian attractive eyes (2 vs 2.21 mm in pretarsal show; 1.438 vs 1.58 for palpebral aperture height/upper lid show ratio; 1.184 vs 1.181 for fold/eye ratio). The attractiveness of 2-mm upper eyelid creases was reasonably confirmed based on these characteristics.

In this study we found that a pretarsal show of 2 mm was deemed the most attractive, while the shape of medium-height double eyelids had minimal impact on aesthetics. This finding held significant guidance for upper blepharoplasty. Currently, patients tend to express their preference for a 6- or 7-mm-high double eyelid, indicating an increased public awareness of the demand for quantifying the upper eyelid crease's height. However, what they refer to as “height” pertains to the distance between the upper eyelid crease and the eye fissure when the eyes are closed, whereas what truly matters is the height when the eyes are open—an aspect that has rarely been explored in the literature. Actually, clinicians usually use the crease height maker or a simple paper clip when discussing the crease height with patients, and low crease heights of 2 or 1 mm are more often chosen. The formula proposed by Barmettler et al establishes a correlation between the heights of upper eyelid creases in the open and closed states, thereby augmenting the significance of this study in investigating the optimal height of upper eyelid creases during eye opening.¹⁵ However, it should be noted that this formula was developed based on data from Caucasians and may not be directly applicable to Asian individuals. The proposed ratio of 1.2:1 by Burusapat and his colleagues defines the optimal position of the upper eyelid crease in Asians, quantitatively describing the height relationship between the upper eyelid crease and upper lid show when the eyes are closed.¹⁰ Nevertheless, there had been no direct study in which the ideal height of double eyelids with open eyes was determined, as we did. Based on our findings, future research may focus on exploring surgical techniques that can effectively achieve the desired height of double eyelids when the eyes are open. This would make a significant contribution to the advancement of blepharoplasty.

The study still had several limitations. First, only 1 model’s image was selected for the questionnaire survey, making it difficult to analyze the impact of factors such as palpebral aperture height on the optimal height of double eyelids. Additionally, all subjects were recruited online, indicating a potential sampling bias toward individuals with higher knowledge or economic status. Third, there was an uneven gender distribution among the subjects, and only Chinese participants were included, limiting the generalizability of the results. Nevertheless, in this study we successfully achieved a well-balanced age range across different subgroups and established an aesthetic theoretical foundation for double eyelid surgery.

CONCLUSIONS

In the present study we have confirmed the optimal characteristics of the double eyelid, that is a 2-mm-high upper eyelid crease with an in-fold shape. Additionally, the attractiveness of 1-mm and 2-mm pretarsal show remained unaffected by morphology. Valuable insights into the aesthetics of the double eyelid have been provided by this study, with significant implications for periorbital aesthetic evaluation, surgical design, and outcome assessment in future double eyelid surgery.

Supplemental Material

This article contains supplemental material located online at www.aestheticsurgeryjournal.com.

Acknowledgments

Drs Chi and Li made an equal contribution to this work as co-first authors.

Disclosures

The authors declared no potential conflicts of interest with respect to the research, authorship, and publication of this article.

Funding

The work was supported by National High Level Hospital Clinical Research Funding, grant nos. 2022-PUMCH-B-041, 2022-PUMCH-A-210, and 2022-PUMCH-C-025.

REFERENCES

Author notes