| BACKGROUNDThe periocular region is the most decisive segment for the facial attractiveness, also plays a powerful role in both ethnic and individual identity. As often be seen in various media, a portrait of a person with mosaic periocular area cannot be identified even. Eyes can express different emotions, responses and interest though different degree of exposure of white sclera and black iris, which is managed mainly by the movement of upper eyelid.An eyelid with well-defined crease is considered universally to be conforming to aesthetic standards. But the reality is that almost half of the Asian women are born with no crease or unsatisfactory crease. Therefore, it is not surprising that the creation of eyelid crease has been the most popular plastic surgery procedure for several decades in Asia. Meanwhile, the rapid development of economy accompanied with increasing competitive pressure of society, and more open values for beauty will result in absolute growth in demand for the procedure.The anatomic characteristic of Asian eyelid and the causative factor of double eyelid crease have been well studied. Accordingly, considerable progress has been achieved in surgical technique since the unremitting efforts of plastic surgeon all over the world/worldwide, especially Korean, American and Chinese surgeon. To this day, it is not difficult any more to create simply a lid crease in a single eyelid; but in contemporary environment only a functional and natural-appearing eyelid crease could satisfy mostly patients, also a responsible surgeon. But some problems in blepharoplasty keep unsolved, even have always been ignored, intentionally or otherwise.In upper eyelid blepharoplasty, the width of lid crease is very important parameter for beauty, and also is the main concern of patients seeking cosmetic double eyelid procedure. In addition, the crease height is the most important determinant of crease width and crease shape. However, in our review of literature, we found that when counseling patients or performing blepharoplasty, to the selection of crease height, the following statement has been widely regarded as the guideline:5 to 6mm creates a low lid crease; 7 to 8mm creates a moderate lid crease; 9 to 10mm creates a high lid crease. Many other standards are almost exactly the same with above-mentioned, only the value varies slightly. There are no commentaries associated with these statements about the reason why the designed crease line should be located at these positions. Moreover, the value of crease height given is only that at mid-pupillary axes across the whole eyelid; there are no recommendations about the accurate values at the other part. Therefore, in performing double eyelid procedure, these values are determined absolutely according to surgeons’ personal experience.There is no doubt that the value at mid-pupillary axes could be used as reference to determine the position of crease at the other section, but the relationship between eyelid crease height at mid-pupillary and that at the other part hasn’t been determined until now. Therefore, still, the position of crease at the rest segment is determined based on individual clinical experience. The potential basis of these statements is that crease height is the only significant factor affecting crease width. A lot of research showed the causative factor of Asian double eyelid is diverse. Likewise, we consider that the determinant of crease width is various, rather than the only crease height.Meanwhile, a youthful, natural-appearing eyelid with attractive crease, which is almost the same as the native one, is exactly the desiring of the Asian individuals who pursue upper blepharoplasty. Luckily, in contrast to the commonly describled statement that Asian universally posses single eyelid with narrow palpebral fissure, full characteristic, in fact, inherent eyelids with well-defined crease occupy a certain proportion in the population.Therefore, we try to study in detail the properties of inherent double eyelid crease and associated factors in order to provide valuable references for plastic surgeon to achieve the most natural-looking result while maintain ethnic characteristic.MethodsA total of 32 healthy Chinese women aged 19-26 who had inherent double eyelid crease were recruited. All the volunteers included hadn’t undergone any periobital procedure for cosmetic, also hadn’t any congenital or acquired eye diseases. The study was fit the rule of the 1975 Declaration of Helsinki and informed consent were obtained.Photographs and Relevant Variables MeasurementsThree landmarks were marked on the surface of the eyelid skin with a brow-pencil when the eye was gently closed. The three landmarks were the intersection of the lid crease line and the vertical line through the lateral limbal, mid-pupillary and medial limbal point. In fact, in our study, almost all the creases line (3/64) could be viewed obviously when the eye was in gently closed position. The only ambiguous crease got clearly the moment the subject opened her eye slightly.The volunteers were asked to sit down in the front of a standard blue background and look at the front lens horizontally. The assistant held a millimeter-guage ruler vertically next to the orbit. The photographs of both eyes, open and closed, were taken by a Nikon D-90 camera (Nikon Corp, Tokyo, Japan) with 160cm object-lens distance,72mm focal distance. All the photographs were performed by a constant photographer.The measured items were as follows:(1) Upper eyelid crease width at 5 levels, the vertical distance between the superior palpebral crease and the eyelid margin in the vertical axis though pupillary center, lateral limbus and 5 mm lateral to lateral limbus, medial limbus and 5mm medial to medial limbus when the eye was open.(2) Upper eyelid crease height at 5 levels, the vertical distance between the superior palpebral crease and the eyelid margin in the vertical axis though papillary center, lateral limbus and 5 mm lateral to lateral limbus, medial limbus and 5mm medial to medial limbus when the eye was closed.(3) Upper eyelid movement distance, the distance that the upper eyelid margin moved in the mid-pupillary axes from gently closed position to primary position.(4) Medial end of the crease to endocanthion (MC-EN), the vertical distance from the interal extremity of crease to the vertical line through endocanthion.(5) Lateral end of the crease to ectocanthion (LC-EC), the vertical distance from the lateral extremity of crease to the vertical line through ectocanthion.If the medial end of the crease was found to be lateral to endocanthion, the MC-EN was assigned a negative value; if medial to endocanthion, a positive value was assigned. On the contrary, if the lateral end of the crease was found to be lateral to ectocanthion, the LC-EC was assigned a positive value; if medial to ectocanthion, a negative value was assigned. The line connecting bilateral medial canthus was difined as the horizontal baseline. If multiple creases were showed, the most complete and highest one was regarded as the standard line. The pixel units dimension was measured using Adobe Photoshop CS5 (Adobe Systems Inc., San Jose, CA, U.S.A.) and we acquired the real world values by arithmetic conversion as following:Formular 1:D(mm)=PD1×10(mm)/PD0D:actual distance; PD1:pixel distance; PDo:pixel distance of 10mm in each photographMRI and eyelid thickness measurementT1 weighted Magnetic Resonance (MR) images were obtained by a Philips INTERA ACHIEVA 3.0 T superconductive MRI system with a short spin echo sequences (echo time=16 ms, repetition time=400 ms). The scanning plane was an oblique sagittal direction that was parallel to the optic nerve axis and 1.5mm thickness without gap. MRI was performed when the eyelids were naturally open and gently closed respectively.The MR image through the center of optic nerve was selected for analysis by using RadiAnt DICOM Viewer R 2.2 software. The thickness of eyelid tissue thick (preaponeurotic or pretarsal tissue, including preaponeurotic fat, orbit septum, submuscular fibro-adipose tissue, orbicularis oculi muscule, subcutaneous fat and skin) at 5 mm,7.5 mm,10 mm,15 mm from the eyelid margin were measured. The line connecting the apex of corneal surface and the center of optic disc was regarded as the horizontal reference line. If the angle between this defined reference line and the inferior edge line of MR image was less 5°, for simplicity, we regarded the edge line of image as the horizontal baseline.StatisticsThe one way ANOVA (normality and equal variances assumed) and Kulskal-Wallis test (normality and equal variances not assumed) were used for comparison between groups (≥ 3). Multiple stepwise regression analysis was used to determine the correlation of lid crease width and lid crease height, distance and thickness at pupillary central axes. The stepping method criteria required probability of F-statistics as "0.05" to enter a variable and probability of F-statistics as "0.10"to remove a variable at each step. All statistical computations were performed using SPSS Windows version 19.0 software (SPSS, Inc, an IBM Company, Chicago, Illinois). All tests were 2 tailed and differences between groups were considered significant for all statistical analysis if p was less than 0.05.RESULTSThe difference of lid crease height, width and proportions among the 5 measured points were statistically significant (p< 0.001). For the crease width, the values at 5 mm laterally from lateral limbus, lateral limbus, pupillary center, medial limbus and 5 mm medially from medial limbus were 4.1 mm.3.4 mm,3.1 mm,2.8 mm,2.1 mm, respectively. The value at the papillary center (mean,3.1 mm) was larger than at 5mm medially from medial limbus (mean,2.1 mm) and medial limbus (mean,2.8 mm), but only reached statistical significance comparing with that at 5 mm medial limbus (p< 0.001); and was smaller than at 5 mm laterally from lateral limbus (mean, 4.0 mm) and lateral limbus (mean,3.4 mm),but only reached statistical significance comparing with that at 5 mm lateral limbus (p< 0.001). Among the five measured points, the value at 5 mm-medial limbus was the least and the value at 5 mm-lateral limbus was the largest, which were confirmed by comparing the two least values (p= 0.001) and the two largest value (p< 0.001) respectively. In five of the 64 double eyelids, the value at 5 mm-medial limbus was 0, that is to say the crease disappeared absolutely at 5 mm-medial limbus. There was an obvious increasing trend in the lid crease width from 5 mm-medial limbus to 5 mm-lateral limbus.The height of eyelid crease at 5 mm laterally from lateral limbus, lateral limbus, pupillary center, medial limbus and 5 mm medially from medial limbus were 5.6 mm,6.8 mm,7.2 mm,6.1 mm,3.8 mm, respectively. The value at pupillary center was greatest among the measurements (5 mm-lateral:p< 0.001, medial:p< 0.001,5 mm-medial:p< 0.001), but the result was not statistically significant comparing with that at lateral limbus (p=0.077). The eyelid crease height at lateral limbus was significantly higher than that at medial limbus (p=0.004). Similarly, the height at 5 mm-lateral limbus was also significantly higher than that at 5 mm-medial limbus (p< 0.001). In this study, we did not examine the precise position at which the crease height was the largest, but it was observed that the peak of crease was between pupillary center and medial limbus.For the ratio of eyelid crease width and height at the corresponding position, the value at 5 mm laterally from lateral limbus, lateral limbus, pupillary center, medial limbus and 5 mm medially from medial limbus were 0.73,0.51,0.43,0.46,0.53, respectively. The value at papillary center was the smallest among the 5 measured points (5 mm-lateral:p< 0.001, lateral:p=0.024,5 mm-medial:p=0.005, respectively), but the result was not statistically significant comparing with that at medial limbus (p=0.386). The value at 5 mm-lateral limbus was significantly larger than that at 5 mm-medial limbus (p< 0.001). The mean value at lateral limbus was 0.50 and at medial limbus was 0.46, without statistical significance (p=0.160).For ULMD, the mean value measured was 9.3 mm; it was obvious that the parameter is smaller than palpebral fissure height. Cho et al. reported the value of palpebral fissure height was 10.8 mm in Chinese American aged 27 to 31 years old, which was larger than that of ULMD. All (64/64) the lid crease lines were identified to extended laterally beyond ectocanthion on temporal side (mean,3.5 mm), whereas most (61/64) did not reach endocanthion on nasal side (mean,-1.6 mm).The thickness of eyelid at 5 mm,7.5 mm,10 mm,15 mm from the eyelid margin was statistically different (p< 0.001). The average thickness at 5 mm from the lid margin was 2.1 mm and at 7.5 mm from the lid margin was 2.4 mm, without significant difference (p= 0.112). The thickness at 15 mm from the eyelid margin was significantly thicker than at 10 mm from the eyelid margin (p<0.001).The result of multiple linear regression of lid crease width, with crease height, crease thick and upper eyelid margin movement distance (ULMD) in mid-pupillary axes as independent variables showed that lid crease width was significantly correlated with the three independent variables. Also, it was identified that crease height was a positive and more effective factor to crease width, whereas tissue thick and ULMD were negative and less effective compared with crease height. The result of variance analysis showed that the regression model was significant (F= 16.046, p < 0.001) and all the three partial regression coefficients are proven to be significant. The determination coefficient R2 was 0.667, which indicated that as much as 66.7% variation in crease width was explained with the help of the three independent variables.DISCUSSIONThe anatomic properties of typical inherent Asian eyelid crease were demonstrated though photograph metric and radiographic measurement. Although the sample size of our study was relatively small, the data obtained still was representative because the subjects in the study were relatively homogeneous population with a small range of age, only female involved. Moreover, neither did we intend to investigate the incidence rate of lid crease, nor to show only the frequency of different types of crease. All the volunteers included in the study signed up independently and proactively after seeing our description which was entitled "recruitment of volunteers who have natural double eyelid crease" and published in the capture. The term "natural" has the meaning of "beautiful" in contemporary Oriental thoughts. Therefore, maybe it was reasonable for us to consider the lid crease studied beautiful, or at least the volunteers considered themselves to be having beautiful lid crease.Meanwhile, young women make up most of the patients who seek double eyelid blepharoplasty, and they desire exactly attractive and unartificial appearing postoperatively. That is, the result and conclusion obtained in this study are based on attractive and inherent double eyelid of Asian women in physiological status, rather than that of older age groups, almost the whole population or cadaver specimens. Thus, the result matches better with clinical application and is greater reference for plastic surgeon to create an attractive, natural-looking eyelid crease.For crease width, Cho et al. reported mean values of 3.7 mm at medial limbus, 3.9 mm at mid-pupillary axes,4.6 mm at lateral limbus in Asian American aged 27 to 31 years old, whereas our research reported mean values of 2.8 mm at medial limbus, 3.1 mm at mid-pupillary axes,3.4 mm at lateral limbus. These values were smaller than that of study by Cho et al, but both showed the tendency that the double eyelid flared up laterally. For the crease height at mid-pupillary axes, Park et al. reported a mean value of 6.5 mm in Asian adult females above 20 years old. Cho et al. reported mean values of 7.1 mm in Chinese American and 7.2 mm in Korean American. The present study showed a similar result with 7.2 mm average value.It was found that the ratio of crease width to height at pupillary axes was 0.43, in agreement with previous report by Cho et al. It is worth noting that the ratio at 5 mm laterally from lateral limbus was largest among the 5 measured points. The higher ratio may indicate higher "conversion" rate of crease height to crease width. The extent of pretarsal skin show near medial canthus was smaller, meanwhile the ratio at the same section was larger (5 mm medially:0.53). Therefore, when designing the crease line at medial part of the eyelid, the line should be marked at a lower position. Possibly for this reason, Xu et al. recommended that the arc of the curve designing line at medial aspect should not be very round. The ratios at other 4 points were investigated in the study to provide richer data for designing crease line.Up to now, to the designing of crease height for achieving prospective double eyelid morphology, specially the crease width, many statements have been postulated, but all of them give few objective data. In clinical practice, the following statement has been widely regarded as the guideline:5 to 6 mm creates a low lid crease; 7 to 8 mm creates a moderate lid crease; 9 to 10 mm creates a high lid crease. Many other standards are almost exactly the same with the standard above-mentioned, only the value varies slightly. There are no commentaries associated with these statements about the reason why the crease should locate at these positions. Another commonly applied method is as follows:position a paperclip or toothpick on eyelid skin surface when the eyes are closed; with the eye opened, gently invaginate the skin to simulate and validate whether the appeared crease is at the desired level or not. But the magnitude and direction of force are highly variable, which has a major impact on the simulated crease morphology. Some hold that the crease should not be placed higher than two-third the height of superior palpebral (the distance between upper eyelid margin and inferior margin of eyebrow in the papillary axis when the eye is open). Although all the designing methods are widely applied in practical clinic, and proved to be effective, however, these designing methods are largely based on surgeons’personal experience or lacking of individualized consideration, which may account for the high rate of complication postoperatively, specially the asymmetric appearing of eyelid crease.The result of multiple linear regression showed that the direction of partial regression coefficient of eyelid thick and ULMD in the regression model is negative. This result suggested that, when other condition is equal, the lager the value of ULMD is, the smaller the value of crease width will become. The conclusion is similar for the relationship between eyelid tissue thick and crease width. As commonly recognized, the crease height was demonstrated accurately to be the greatest weight among the three main determinants of crease width. Among the three correlated factors, the crease height and eyelid tissue thick are the variables that surgeon could manage to construct specific size and shape of double eyelid. The ULMD should not be changed unless the ptosis was diagnosed.Surgeons having some experience in creation of double eyelid have been confused by the phenomenon occurred occasionally that although the designed crease height was the same preoperatively (different eyelids in one individual or different individual), and the removal of skin and eyelid tissue were conservative and consistent, the acquired crease width was different. Therefore, we hypothesized the determinants of crease width were various rather than the only designed crease height, given that the causative factors are multiple. The result of our study confirmed this hypothesis and showed that eyelid thickness and ULMD were also the associated factor of crease width. Based on the partial regression coefficient of each independent variable, the designed crease height was the greatest weight factor, which might be the major reason that why satisfactory postoperative outcome could be acquired frequently, although only rely on crease height when performing double eyelid surgery.Allen et al. found palpebral fissure height (PFH) and margin reflex distance (MRD) were correlated with the degree of definition of eyelid crease in blepharoptosis. AHN et al. found that function of levator palpebrae superioris muscle was one of the factors that determined crease width and its formation. PFH and MRD could be considered as the indicator of levator function (LF) in some extent, and the most accurate indicator for judging the degree of LF was the excursion of upper eyelid from downgaze to upgaze position. Nevertheless, in the regression analysis, we suggested a newly defined parameter, ULMD, as an independent variable indicating the degree of LF. The ULMD is distance the upper eyelid margin moves from gently closed position to primary position. This defers from PFH which is the distance between upper eyelid margin and lower eyelid margin in the mid-pupillary axis when the eye is open. PFH includes the distance that lower eyelid moves during opening the eye, which has no influence to topographical appearance of the upper eyelid. The parameter is also different from the excursion of upper eyelid from downgaze to upgaze position. However, the status, deciding whether a eye is attractive or not, is based on the morphological variation of upper eyelid from gently closed-eye position to natural open-eye position, rather than from downgaze to upgaze position. Therefore, it is more reasonable to adopt the ULMD as the representative parameter to explore the possible influence of levator function to the width of double eyelid crease.A mechanical analysis of eyelid morphology demonstrated large eyes (opening angle of eye) favor of the formation of eyelid crease, the large eyes have same meaning with large value of ULMD. According to the result of multiple linear regression in our study, a consistent conclusion was confirmed in normal eyelid. Furthermore, we found that when the normal opening angle of eye is enough to make the soft tissue fold up, the visible height of pretarsal skin (i.e., eyelid crease size or crease width) will gradually decrease as ULMD gets larger.In total, the eyelid thickness was relatively homogeneous at the segment at least below 7.5 mm, but it increased significantly at latest at the level of 10 mm from lid margin. Multiple linear regression analysis showed that eyelid thickness was negative influence to crease width. Based on previous research results, and imaging anatomic properties showed in this paper, we explain the mechanism as follows:the thicker the tissue above crease line is, the more the preseptal tissue tends to fold up, rather than move orientating superiorly and intraorbitally. The folding up will resulting in more pretarsal skin hooded over, thus diminishing visible height of pretarsal skin.The skin redundancy occurs commonly in Asian single eyelids, therefore a proper amount of skin has always been excised in double eyelid procedure. However, we did not consider this obvious factor when analyzing the correlated factors of crease width, because the objects included almost did not exhibit skin redundancy.Although we demonstrated the critical factors affecting crease width, even investigated the linear relationship between crease width and associative factors, it is still difficult to achieve a precise predictable surgical algorithm in practical clinical application. In other words, at present the plastic surgeon cannot create a double eyelid to meet patient’s exact specifications because the eyelid tissue is viscoelastic material, to a certain extent, some slight changes during procedure have subtle effect on the characteristic of eyelid crease. For example, when closing the incision, if suturing the inferior skin of incision to higher and deeper position with obvious tension, the crease will be wider and appear prominent.In the present study, we demonstrate critical determinants of crease width and their respective influence direction and force, give normal value of various parameters (crease width, crease height, ratio of crease width to height, UEMD, tissue thick and other relevant anatomic particularities) in vivo with the eyes closed and open respectively. The result obtained in the paper may provide useful insights for Asian blepharoplasty, to achieve a natural-appearing and youthful eyelid crease.CONCLUSIONSMore complete measurements of double eyelid in beautiful and Asian young women, in conjunction with photographs and corresponding MRI are presented. In surgical planning for upper blepharoplasty, referencing to these data from inherently lid crease will be useful for achieving natural-appearing crease. Specially, it is imperative to take into account not only crease height, but also eyelid crease thick and upper eyelid margin movement distance (ULMD) among individuals when planning crease line for prospective size and shape of crease. |
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