In the first XXI century 10 years, among the issues of the eyelids anatomy, journal publications reflected postnatal development and involutive changes of the eyelids [2, 5, 8], the anatomical structure of the tarsal (Meibomian) glands [7, 12], considerable attention was paid to the eyelids clinical anatomy, including various types of their pathology [9, 10, 13, 14, 15, 16]. A study on ultrasound eyelids biomicroscopy under normal conditions and in congenital ptosis is highlighted . In 2003—2017, a number of manuals, atlases, and textbooks containing special sections on the eyelids morphology were published in Russian and foreign literature [1, 3, 4, 6, 11, 16]. Most of them, as well as in journal publications, describe the eyelids structure at the macroscopic and microscopic (mainly cytological) level. There are almost no descriptions and especially photos of preparations at the macromicroscopic level, i.e. at small magnifications of a stereoscopic microscope corresponding to the optical magnifications of operating microscopes. Such macromicroscopic studies could, firstly, fill the "optical range" in the morphology of the eyelids, and secondly, be the anatomical basis for microsurgical interventions on the eyelids. Methodically, the histotopographic method widely used in recent decades would be useful in solving such a problem . In this regard, the purpose of this study is to obtain data on the macromicroscopic anatomy of the eyelid structures of the eye and to present photos of the eyelid structures in the macromicroscopic range.
Material and methods
The material of the study was 24 complexes, including the upper and lower eyelid, medial or lateral angle of the eye, obtained from 12 mature and elderly people subjects who died from causes not related to the face or vision organ pathology. The material was obtained in accordance with Article 68 "Use of the body, organs and tissues of a deceased person" of the Federal Law "On the basics of protecting the health of citizens in the Russian Federation" and Russian Federation Government Decree No. 750 of July 21, 2012. "On approval of the rules for the transfer of unclaimed body, organs and tissues of a deceased person for use in medical, scientific and educational purposes."
The study used a histotopographic method, including the preparation of serial, spatially oriented histotopograms, their staining with Van-Gieson picrofuxin and hematoxylin-eosin, studying, morphometry and photographing under a stereoscopic microscope MBS-10 at 6-and 12-fold increase.
Results and discussion
On cross histotopographic of the upper and lower eyelids (Fig. 1A and B) eyelid main layers are well-defined: skin, subcutaneous tissue, eye circular muscle eyelid part, the eyelid cartilage and conjunctiva (pictured top to bottom Fig. 1A, Fig. 1B from the bottom up).The upper and lower eyelids thickness is 2.6—3.2 mm. The main layers of the upper and lower eyelids thickness is: skin-0.7—0.9 mm, subcutaneous tissue-0.8—1.0 mm, the eyelid part of the circular eye muscle-0.7—1.1 mm, tarsal plate-0.8-0.9 mm, conjunctiva-20-35 microns.
Fig. 1. Transverse histotopograms of the upper (a) and lower (b) eyelids.
Coloring according to Van Gieson, magnification MBS-10, eyepiece 6, objective 2.
Eyelid skin is well detected at histotopographic stained with hematoxylin-eosin. In the areas where the eyelashes come out or the excretory ducts of the sweat glands open, it has a wavy contour, because it contains numerous depressions from the outgoing eyelashes and openings of the ducts of the glands (Fig. 2A). The skin over the greater length of the eyelids forms a smooth surface on the upper and lower eyelids (Fig. 2B).
Fig. 2. Histotopograms of the surface layers of the upper eyelid.
a, b — skin and subcutaneous tissue with eyelash follicles, stained with hematoxylin and eosin, magnification MBS-10, eyepiece 6, objective 2; c — bulbs and the beginning of eyelashes in the subcutaneous tissue, staining according to Van Gieson, magnification MBS-10, eyepiece 6, objective one; d — sebaceous glands (Zeiss), staining with hematoxylin and eosin, magnification MBS-10, eyepiece 6, objective one; e — detail d, magnification MBS-10, about 6, objective 2; f — sweat glands (Moll), staining with hematoxylin and eosin, magnification MBS-10, eyepiece 6, objective 2.
Subcutaneous tissue contains eyelash follicles, sebaceous and sweat glands.
The eyelashes follicles are located in subcutaneous tissue at different depths, forming from 2 to 5 layers. In separate observations, the location of follicles between the marginal muscle bundles of the eyelid part of the upper eyelid muscle was noted. On the above histotopograms Fig. 2A and Fig. 2B, stained with hematoxylin-eosin, the follicles are represented by rings or ovals with an intensely colored cell layer and the root of the eyelash located inside the ring. Otherwise look follicles of the eyelashes on histotopographic, van gieson's stain (Fig. 2E). On such preparations, the intravascular rods of the eyelashes are colored, their location at different depths of the subcutaneous tissue is clearly visible. The outer diameter of the follicles (eyelash bulbs) can reach 0.9 mm. The depth of the location in the subcutaneous tissue is 1.5—2.2 mm, the density of the location is 3—4 in 1 mm2.
Sebaceous and sweat glands are well detected on a histotopogram with predominant hematoxylin staining.
In Fig. 2B and Fig. 2D, the sebaceous glands are located in direct contact with the eyelash follicle in the surface layer of subcutaneous tissue, at a distance of 0.3—0.5 mm from the skin. As a rule, one follicle has two glands with excretory ducts that open directly into the follicle. The transverse size of the sebaceous gland is 0.3—0.7 mm. It is represented by a cluster of lobes with converging flows to the eyelash follicle. This structure is clearly visible at 12x magnification (Fig. 2G). The sebaceous glands density of thesis 2—3 glands in 1 mm2.
Sweat glands are located in the deeper layers of subcutaneous tissue, at a depth of 0.4—1.1 mm, usually deeper than the sebaceous glands. The sweat glands density is 1—2 mm2. The gland has the twisted ball form, with a diameter of 0.5—0.9 mm (Fig. 2D).
The eye circular muscle' eyelid part in the upper and lower eyelids is a muscle with transverse layers on the plane-eyelid arrangement of muscle fibers, assembled into muscle bundles (Fig. 3A and Fig. 3B).
Fig. 3. Histotopograms of the secular part of the circular muscle of the eye and the tarsal glands of the upper eyelid.
Coloring according to Van Gieson, magnification MBS-10, eyepiece 6, objective one.
a, b — differences in the bundle structure of the muscle; c — tarsal glands of the upper eyelid; d — detail c, eyepiece 6, objective 2.
The muscle bundles diameter is 20—80 microns. Muscle bundles are located parallel to each other along the eyelid plane and length. The muscle bundles arrangement density can vary from a dense arrangement to a loose one with the bundles separated by significant layers of connective tissue. The edge of the muscle in the upper eyelid does not reach the edge of the eyelid, been separated from it by a significant layer of subcutaneous tissue. In the lower eyelid, it can almost come close to the edge of the eyelid. Behind the muscle layer is a thin layer of connective tissue up to 80 microns thick, separating it from the tarsal plate.
In the upper and lower eyelids cartilage on the planar histotopograms stained by Van-Gieson, tarsal (Meibomian) glands are perfectly revealed (Fig. 3B and G). Each gland has the form of multiple lobes located around and along the gland duct, located in the cartilage plane and heading to its edge. The length of each gland in the cartilage's middle of the upper eyelid is 2.8—3.0 mm, the lower eyelid — 2.0—2.6 mm. The glands length decreases towards the medial and lateral ends of the cartilage. The tarsal gland diameter is 0.8 mm.
Hysterograms allow to reveal certain details of the structure macro- and microanatomical eyes corners.
Thus, medial angle cross sections with lacrimal pathways: lacrimal tubules, lacrimal sac, nasolacrimal duct, and lacrimal muscle are shown on Fig. 4. At the histotopograms is shown that the lacrimal sac has an irregular oval shape with an wall angular contour, and the nasolacrimal duct has an irregular rounded-quadrangular shape with a sinuous edge. We cannot say that this is their lifetime form of lumen, because here the influence of formalin fixation of the material is possible.
Fig. 4. Histotopograms of the zone of the medial angle of the eye and lacrimal ducts.
Staining with hematoxylin and eosin. magnification MBS-10, eyepiece 6, objective 2 (c — eyepiece 6, objective 1).
a — lacrimal meat; b — the lacrimal canal; c — the area of the medial angle; d — detail B; lacrimal sac and lacrimal canal; e — nasolacrimal duct.
Important details are identified on the eye lateral corner histotopograpms.
First of all, the relationship between the lateral angle apex and the orbital region lateral surface skin is of interest (Fig. 5A and Fig. 5B). As it can be seen on the histotopogram, the distance between the lateral angle top and the orbital area skin, especially if there is a transverse fold on it, can be only mm. In other extreme cases, this distance may be equal to mm.
Another detail concerns the upper and lower eyelid muscles lateral ends. It is generally accepted that muscle bundles in the eye lateral corner are attached to the eyelids lateral ligament, as it is shown at the Fig. 5B. However, as can be seen on the presented histotopograms (Fig. 5G, 5D, 5E) the muscle bundles part can pass from the upper eyelid to the lower one or vice versa, continuing or ending there.
Fig. 5. Histotopograms of the lateral angle of the palpebral fissure. magnification MBS-10, eyepiece 6, objective 1.
a, b — differences in the relationship of the lateral angle with the skin of the orbital region, staining with hematoxylin and eosin; c—f — differences in attachment and relationships of muscle bundles of the upper and lower eyelids of the secular part of the circular muscle of the eye, staining according to Van Gieson.
The data presented in general form indicate the testified of using the histotopographic method to study the macromicroscopic anatomy and microtopography of the eyelids. The method allows to document the information obtained by histotopograms' microphotographs at selected magnifications of a stereoscopic microscope. On this basis, a eyelid structures micrographic images series in the macromicroscopic range was obtained.
As a result of the study, morphometric data on the macromicroscopic structures of the eyelids were obtained: the eyelashes follicles, sebaceous, sweat, tarsal glands, the eye circular muscle' eyelid part. Greatly new information is obtained about the macromicroscopic of anatomy and microtopography of these formations, the differences in distance between the lateral angle top and the orbit region skin, inter-eyelids transitions muscle bundles of old parts of the upper and lower eyelids. The presence of thin connective tissue layer between the muscle and the cartilage of the eyelid anatomically proves the possibility of surgically separating eyelid on musculocutaneous and tarso — conjugated parts in plastic surgery on the eyelids.
The obtained data applied meaning could be seen in it's using as an integral part of the microsurgical interventions anatomical basis on the eyelids, especially in reconstructive and plastic surgery.
Thus the morphometric parameters of the main structures of the eyelids, the features of their microtopography are presented in the article. The resulting complex of morphometric, macro microscopic data and images of intra-eyelid structures complements and develops the eyelid' macromicroscopic anatomy and microtopography. It is important for further detailing the anatomical structure of the eyelids and is of interest for modern ophthalmic microsurgery.
The participation of the authors:
Research concept and design — I.I. Kagan
Collection and processing — I.I. Kagan, E.A. Bazhitova
Statistical processing — I.I. Kagan, E.A. Bazhitova
Writing — E.A. Bazhitova
Editing — I.I. Kagan
The authors declare no conflicts of interest.