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You are watching: How many eyelashes do we have

StatPearls . Sweetheart Island (FL): StatPearls Publishing; 2021 Jan-.


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Anatomy, Head and Neck, Eyelash

Bhupendra C. Patel; Michael J. Lopez; Zachary P. Joos.

Author Information

Introduction

The Greek word because that eyelid is “blepharon,” from i m sorry is obtained the prefix "belpharo," which has been in use due to the fact that antiquity. The Greek for an eyelash is “blepharida” which is no used in medication today. The Latin for eyelid is “palpebra” and also that for eyelash is “cilium” a word only in use because the beforehand 18 century.

Eyelashes and also eyebrows are essential anatomical structures which are main not just in the confront but main to all perceived human interactions. Eyebrow movement conveys emotions (sad, happy, angry, surprise, pensive, etc.) and eyebrows defend the eye by be sure the “curtain rods” the they effectively are when tired, thereby relaxing the top eyelid skin and also contributing to lid closure and eye protection. Eyebrow hair direction offer to defend the eye from particulate matter and also sweat.

Eyelashes and also eyebrows have constantly been critical part of facial beauty. They have been plucked, accentuated and also modified in innumerable ways to boost the beauty of the face and eyes in certain in plenty of cultures. The Egyptians and also the Indians have actually used products like kohl to boost brows and lashes for centuries. The emphasis of the eyes manifests in the contemporary world v the usage of mascara, eyeliner, and eyeshadow. Curlers are supplied to exaggeration the herbal curve that lashes. Although long lashes space prized in many cultures, specific cultures (the Hazda, the last of the hunter-gatherer people of Tanzania) trim their lashes.

Comparative Anatomy

Mammals have eyelashes; some, choose the camel, have profoundly long lashes, lengthy used come accentuate features in cartoons. Cows have long directly lashes which are medially oriented. A summary of “cow lash deformity” is offered when viewed as a complication that blepharoplasty, often affecting the lateral third of the top eyelid.<1> Other big mammals favor horses also have similar long, relatively straight lashes.

The eyelash viper is claimed by part in south America to wink after striking that victim. The “lashes” room not lashes, but modified scales above the eyes. And, of course, snakes cannot wink together they have no eyelids!


Structure and also Function

Surface Anatomy

In humans, there space 75 to 80 lasheson the lower eyelid., and also the top eyelid has 90 come 160 lashes. Lash length is variable from individual to individual: they carry out not grow beyond a details length (usually much less than 12 mm) and also then fall off by themselves. Existing thinking is that lash length is limited because the growth rate and the anagen phase are shorter than scalp hair. Eyebrow hairs might be longer, particularly with age (Denis Healey brows). Eyelashes generally execute not need trimming unless there is too much growth (trichomegaly). Ms. Girlfriend Jianxia the Shangai stop the world document for the longest eyelashes in 2018: her lashes measure up 12.40 cm!  after ~ lash remove by pulling, it takes around eight main to flourish back. Eyelash hair is not influenced by puberty.

Lashes curve in all ethnicities. The curvature has been presented to occur since of asymmetric cell types along the concave and also convex sides of the bulb. Similarly, this asymmetry is additionally present in curly hair. The curve of the lashes is much more in Caucasians compared to Asians. Lashes have actually lift-up and also curl-up angles which have been measure photographically producing a phototrichogram.

Cross-sectional Anatomy

Each lash has actually a hair obelisk that extends outside the skin, a source which is under the skin and a bulb which is the enlarged terminal portion. The inferior portion of the pear is in direct contact with the dermal papilla, which has a vascular supply, allowing interactions which result in follicle cycling. The lash has an inside medulla written of cells, a surrounding medulla or cortex, which is stiffer and gives the lash strength and rigidity, and the outer concentric layer which is the cuticle. The cuticle, i m sorry is impermeable, protects the inner part of the lash. 

The outermost layer, the cuticle is 7 to ten great thick and made up of transparent overlapping scales. 

The next layer, the cortex is the thickest portion of the lash and also is composed of keratin.; this layer includes melanin. 

The eyelash follicle (follis, Latin for bag): the term follicle refers to the complicated that is responsible because that hair growth and also is written of the dermal papilla i m sorry is connective tissue v a capillary loop, the germinal hair matrix approximately the papilla and the lash source or bulb. The germinal layer has dividing cells which give rise to the hair, and also the bulb is wherein the process of keratinization begins. The hair follicle embeds in the dermis that the eyelid (which has actually two layers, epidermis and dermis, as opposed to the scalp which has actually an epidermis, dermis and also a hypodermis). Eyelash follicles space 2.4 mm deep in the top lid and 1.4 mm in the lower lid. There are more active lash follicles in the upper lid contrasted to the reduced lid (41% vs. 15%).<2>

The hair ~ above the body has actually arrector pili muscles which straighten the hair in the cold or solution to a solid emotion (fear, excitement) causing what is generally termed “goose-bumps” or “goose pimples” due to the fact that of the resemblance to plucked goose skin. The lash follicle has actually no arrector pili muscles. Therefore, lashes carry out not change position in these circumstances.

Lash follicles attach to two types of secretory glands:


Zeiss glands are holocrine glands i beg your pardon liberate the complete cell content, sebum, which acts as a lubricant and also has antimicrobial properties.
Glands that Moll space only found in eyelids and also are apocrine, which way the cells fragment, thereby producing secretions which are thought to have antimicrobial properties.

Eyelash Pigmentation

Melanocytes synthesize melanin by melanogenesis. Lashes seem to come to be gray or white much later than scalp hair. Continued expression of enzymes such as tyrosinase-related protein 2 (TRP-2), which impacts melanocytes, is assumed to be the reason. Scalp hair not only suffers depletion the melanocytes by apoptosis and also oxidative tension but additionally reduced expression that enzymes like TRP-2. There has actually not been adequate research on the alters in lash pigmentation with period in various races.

Aerodynamics around Lashes

Eyelashes have vital role in the protection of the eye. Aerodynamic studies have demonstrated the the best lash must be one-third the width of the eye. As well as protecting the cornea native particulate matter, it shows up that the aerodynamic flow of air due to the fact that of the curve and also density the lashes dram a duty in corneal protection. The exact ways in i beg your pardon evaporation might be enhanced or lessened by lashes is unknown. Although in vitro studies have been attempted, there have actually been no in vivo researches performed on person lashes and also corneas. 

Life cycle of Lashes

Lashes flourish at 0.12 come 0.14 mm every day (as compared to scalp hair which grow at 0.2 to 1.1 mm every day). The 3 phases of lash development in the eyelash growth cycle are:

The expansion phase as soon as the root of the hair is splitting lengthening the pillar (anagen) which varies from four to ten weeks

The destruction phase (catagen) throughout which the lash converts come a club hair together the hair is cut off native the blood it is provided 15 days

The resting phase (telogen) which causes shedding of the hair, lasts four to ripe months

Half the eyelashes room in one anagen phase: periocular hair has the shortest anagen come telogen ratio. After the telogen phase, the lash drops out, and also the cycle starts anew v the anagen phase. The entirety lash bike is from 4 to eleven months.

The stages of the life bike of lashes contrasted to the eyebrows and the scalp is as follows:


Lash microflora: Propionibacterium, Streptophyta, Staphylococcus, Corynebacterium, and enhydrobacter are usual bacteria uncovered on lashes. In the existence of blepharitis, Staphylococcus, Streptophyta, Corynebacterium, and Enhydrobacter increase. Ineterestingly, Propionibacteriumis often reduced in the visibility of blepharitis. 

Demodex folliculorum and Demodex brevis are natural parasites which boost in numbers through age. By the period of 70 years, almost 100% of people will have actually these parasites. D. Folliculorum live in eyebrows, scalp hair, ears and eyelashes, whilst D. Brevis is uncovered in the sebaceous oil glands in the face and also in Meibomian glands. Inflammation the eyelids is caused when the parasite die (bursts), releasing its components which is inflammatory. Cylindrical debris is found roughly the lashes and also is pathognomonic that demodex.


Embryology

Condensation the mesenchymal cells first occurs in ~ week nine developing eyelash follicles and also their appendages. In ~ this stage, the tarsal plate and the orbicularis oculi additionally develop together with evidence of blood vessels. By main 12, lot of eyelash follicles have the right to be viewed under the skin and also by main 14, eyelashes together with sweat glands and sebaceous glands appear.<3>


Blood Supply and also Lymphatics

The superior and inferior marginal arteries native the ophthalmic artery supply the upper and also lower eyelids, respectively. The top eyelid marginal arterial arcade is near the follicles that the eyelashes, anterior come the tarsal plate and 2 mm exceptional to the lid margin. The superior arcade lies between the Muller muscle and the levator aponeurosis. The lower eyelid may have one or two arcades, but the arcades are more from the lid margin, at the inferior border that the tarsal plate. The internal carotid artery gives the eyelids via the ophthalmic artery and the external carotid artery v the angular and temporal arteries. Therefore, there is extensive collateral supply from these two systems. 

Venous drainage is pretarsal and also posttarsal: the pretarsal venous drainage is right into the angular vein medially and the superficial temporal vein laterally. The posttarsal venous drainage is into the superior and inferior ophthalmic vein and also the pterygoid plexus and also anterior face vein. 

Lymphatic drainage native the medial eyelids is come the submandibular lymph nodes; the from the lateral eyelids is to the preauricular nodes.


Nerves

The eyelid margin is among the many sensitive parts of the human body as confirmed by the pains experienced throughout the administration of a local anesthetic remove of eyelid margin lesions. Cost-free nerve end envelop the eyelashes. Addition, lanceolate and also circular Ruffini nerve end (also referred to as corpuscles) room present, which provide touch, pressure, vibration, heat, and mechanoreception. Besides eyelashes, the anterior eyelid cutaneous surface has fine vellus hairs: this possess comparable innervation. Furthermore, Meissner corpuscles (sensitivity to light touch) are also found, especially on the occlusal surface of the eyelids. This profusion of intricate innervation provides the lashes and the eyelid margins especially sensitive.<4> The sensitivity of eyelashes is similar to the sensitivity the a cat or computer mouse whiskers with comparable function.


Muscles

Eyelashes lack the arrector chili muscle discovered elsewhere, so the lashes carry out not change position in the existence of cold, emotion, etc. 


Physiologic Variants

Age-related travel in Lashes

Studies that lashes in different age teams have presented that there is a generalised reduction in the thickness, pigmentation, and length of lashes through age but there are few proper longitudinal studies. Thibault enhanced our understanding of lashes and also the adjust over time by studying defined lashes over nine months, measure the length each week.

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Canities is the natural gradual graying of hair shafts because of tyrosine manufacturing decrease in the hair bulb.


Surgical Considerations

Knowledge that the structure and distribution the eyelashes, and also of the depth that the lashes in the upper and lower eyelids is an essential when performing surgical procedure that entails the eyelid margin. 


Clinical Significance

The anatomy the the eyelash different from hair elsewhere in the body in countless respects. Expertise of these differences is essential when addressing eyelid, eyelid margin, and eyelash problems. There are distinct eyelash troubles which room not seen in hair in other places on the body because of the certain anatomical differences and also the relationship of the growth, curvature, and location to the cornea.