The upper eyelid skin is considered to be gradually thicker, going upward [1]. However, we empirically know that skin thickness can vary significantly among individuals. Some have uniformly thin skin, while others have thicker skin, and in some cases, the skin may be thinner in the eyelid margin but thicker further upward. As such, the upper eyelid skin shows various types, but this has not been confirmed in a microscopic study.

The present study aimed to microscopically examine the skin thickness at 5 and 12 mm from the eyelid margin in Asian individuals.

A histological evaluation was performed on 20 upper eyelids (10 right and 10 left) from 14 Japanese cadavers (age range: 36–97 years old, average: 68.9). The specimens were fixed in 10% formalin. The skin thickness was measured at 5 and 12 mm from the eyelid margin and compared. The eyelid margin was defined as the anterior edge of the upper tarsal plate. The part with small skin sulci was judged straight, but that with deeper groves, such as a lid crease, was measured by its whole skin length. Statistical analyses were conducted using the Mann–Whitney U-test, with the significance level set at 0.05.

The method used for harvesting and preparing the eyelid samples was described in a previous study [2]. After appropriate pretreatment for microscopic examination, sagittally sliced sections of the specimens were stained with Masson’s trichrome.

Microscopic photographs were taken using a digital camera system attached to the microscope (Swift Microscope World) and merged using Adobe Photoshop 2024 (Adobe Systems Inc.). The positions at 5 and 12 mm from the anterior edge of the upper tarsal plate and skin thickness were measured on the merged photos using Adobe Photoshop 2024. The skin length in areas with both larger and smaller creases was also measured.

The past medical history and clinical evaluation of the cadavers were negative for previous eyelid or orbital trauma, surgery, tumor, Graves’ orbitopathy, cerebral nerve palsy, or any other periocular pathology. However, no information regarding skin disease was available.

All cadavers were registered with the cadaveric service at Aichi Medical University. The institutional review board (IRB) of Aichi Medical University approved this anatomical study, which was conducted in accordance with the tenets of the Declaration of Helsinki and its later amendments (approval number: 2024-194). The IRB granted a waiver of informed consent for this study based on the ethical guidelines for medical and health research involving human tissues established by the Japanese Ministry of Education, Culture, Sports, Science, and Technology and by the Ministry of Health, Labour, and Welfare. The waiver was granted because this study was an anatomical rather than interventional study. Nevertheless, at the request of the IRB, we published an outline of the study on the Aichi Medical University website that was available for public viewing. This also provided the cadavers’ relatives with the option to refuse to participate in the study, although none did. Personal identifiers were removed from the records before analysis.

The skin at 5 and 12 mm from the upper eyelid margin showed statistically similar thickness (p=0.064).

However, the tendency for the skin to thickness upward was categorized into four types. The first type was much thicker at 12 mm (over 2 times thicker), observed in four eyelids from three cases (Table 1, Fig. 1). The second type was moderately thicker at 12 mm (between 1.5 and 2 times thicker), found in three eyelids in three cases (Table 2, Fig. 2). The next type exhibited similar thickness at 5–12 mm and was divided into two subgroups: one was coherently thin at both positions (less than 0.5 mm, four eyelids from three cases) (Table 3, Fig. 3), and the other was consistently thick at both positions (more than 0.5 mm, nine eyelids in eight cases) (Table 4, Fig. 4).

Figure 1. The type of much thicker skin at 12 mm (more than 2 times thicker). A 36 year-old male specimen in left, sliced around center of the upper eyelid, stained with Masson’s trichrome. ⇨, the anterior edge of the tarsal plate; ☆, 5 mm from the anterior edge of the tarsal plate; □, 12 mm from the anterior edge of the tarsal plate.

Figure 2. The type of moderately thicker skin at 12 mm (between 1.5 and 2 times thicker >). A 36 year-old male specimen in right, sliced around center of the upper eyelid, stained with Masson’s trichrome. ⇨, the anterior edge of the tarsal plate; ☆, 5 mm from the anterior edge of the tarsal plate; □, 12 mm from the anterior edge of the tarsal plate.

Figure 3. The type of similar skin thickness between at 5 mm and 12 mm, with coherently thin at both positions (less than 0.5 mm). A 52 year-old male specimen in right, sliced around center of the upper eyelid, stained with Masson’s trichrome. ⇨, the anterior edge of the tarsal plate; ☆, 5 mm from the anterior edge of the tarsal plate; □, 12 mm from the anterior edge of the tarsal plate.

Figure 4. The type of similar skin thickness between at 5 mm and 12 mm, with consistently thick at both positions (more than 0.5 mm). A 45 year-old male specimen in right, sliced around center of the upper eyelid, stained with Masson’s trichrome. ⇨, the anterior edge of the tarsal plate; ☆, 5 mm from the anterior edge of the tarsal plate; □, 12 mm from the anterior edge of the tarsal plate.

Table 1 . The type of much thicker skin at 12 mm (2 times <).

Site	36ML	38MR	74FL	87ML
5 mm	0.59	0.42	0.20	0.18
12 mm	1.28	1.01	0.56	0.60

M, male; L, left; R, right; F, female..

Table 2 . The type of moderately thicker skin at 12 mm (1.5 times <, 2.0 times >).

Site	36MR	38ML	45FL
5 mm	0.79	0.27	0.40
12 mm	1.23	0.51	0.62

M, male; L, left; R, right; F, female..

Table 3 . The type of similar skin thickness between at 5mm and 12 mm, with coherently thin (both positions, 0.5 mm >).

Site	52FR	52FL	81FR	82FR
5 mm	0.38	0.40	0.40	0.49
12 mm	0.45	0.48	0.41	0.62

L, left; R, right; F, female..

Table 4 . The type of similar skin thickness between at 5 mm and 12 mm, with consistently thick (both positions, 0.5 mm <).

Site	45FR	54FR	54FL	61ML	74FR	79MR	85FL	94FL	97MR
5 mm	0.85	0.61	0.59	1.01	0.53	0.76	0.66	0.78	0.90
12 mm	1.04	0.57	0.70	1.01	0.67	0.71	0.67	0.56	0.66

M, male; L, left; R, right; F, female..

The upper eyelid skin thickness was statistically similar at 5 and 12 mm from the eyelid margin, but four types are also illustrated depending on the skin thickness tendency upward.

The upper eyelid skin is generally thought to thicken as it moves upward [1], but the area in front of the tarsal plate was reported to be similar [1]. Hwang et al. [1] measured the skin thickness at four points in the upper eyelid, cilial area, mid-tarsal area, upper tarsal area, and lower border of the eyebrow. In this study, the second and the third, the same points measured as in our study, showed no significant statistical differences in thickness. In this respect, our results are consistent with previous data.

However, our study further categorized four types of variations of skin thickness tendency upward. The first type was much thicker at 12 mm (over 2 times thicker), the second type was moderately thicker at 12 mm (between 1.5 and 2 times thicker), and the third type showed a similar thickness at 5–12 mm. It was divided into two subgroups, with a coherently thin type at both positions (less than 0.5 mm) and a consistently thick type at both positions (over 0.5 mm).

The differential diagnosis of the above four types can be reliably made with imaging such as magnetic resonance imaging, but this is impractical for daily clinical use. Palpation and inspection are often sufficient for assessing skin thickness. In the thicker tendency type, sub-brow blepharoplasty [3] may be preferred over the pinch technique. In the consistent thickness type, pinch blepharoplasty may be more appropriate.

Using formalin-fixed specimens, we measured the skin thickness at 5 and 12 mm from the upper eyelid margin. In the upper eyelid blepharoplasty, we typically set the incision line at 8 mm from the upper eyelid margin, with skin under tension, and remove 8 to 10 mm of skin under similar tension. Empirically speaking, the area at 8 mm from the upper eyelid margin and the skin removal height of 8 to 10 mm under tension in a living person correspond, when relaxed, to the area 5 mm from the upper eyelid margin and a removal height of approximately 7 mm. Since the specimens in our study had been preserved in formalin for a long time, tissue shrinkage may have occurred over time [4]. Additionally, the skin in a living person can be extended. Therefore, the results of this study may apply to surgical procedures in the operating room.

There are several limitations in the present study. First, the sample size was limited, and all cadavers were Japanese, which may not be representative of the Caucasian population. Second, the study was performed on formalin-fixed specimens, and different outcomes may be obtained using fresh cadavers. It was also difficult to determine the position at 5 and 12 mm from the eyelid margin as several cadavers have deeper groves. Although we did not perform statistical analyses for each of the four types owing to the small sample size, this remains another study limitation.

In conclusion, the upper eyelid skin thickness was statistically similar at 5 and 12 mm from the eyelid margin, but four distinct skin thickness types were identified based on the upward distribution.

None.

The authors have nothing to disclose.