Patel Bhupendra C., Malhotra Raman
University of Utah
Eyelashes develop from ectoderm between weeks 22 and 26 of gestation. Although the length varies from person to person, they do not grow beyond a certain length and then fall off by themselves. They generally do not need trimming unless there is excessive growth (trichomegaly). If a person pulls a lash out, it takes about 8 weeks to grow back. Eyelash hair is not affected by puberty. Eyelash follicles are 2.4-mm deep in the upper lid and 1.4 mm in the lower lid. There are more active lash follicles in the upper lid compared to the lower lid (41% vs. 15%). The function of eyelashes is to protect the eyes from particulate matter. They are also highly innervated, making them sensitive (have been compared to cat's whiskers) to touch and again help protect the eyes. The human lower eyelid has 75 to 80 lashes in three to four rows, whereas the upper eyelid has 90 to 160 lashes scattered on five to six rows. Each lash has a hair shaft that extends outside the skin, a root that is under the skin, and a bulb that is the enlarged terminal portion. The inferior portion of the bulb is in direct contact with the dermal papilla, which brings key mesenchymal-epithelial interactions in follicle cycling. Unlike the scalp, which has the epidermis, dermis, and hypodermis, eyelid skin is thinner with only the epidermis and dermis. Lash follicles also do not have arrector pili muscles which straighten the hair in response to cold or intense emotions. is the misdirection of eyelashes whereby they grow under the skin through to the surface or posteriorly to the conjunctival surface instead of emerging normally from the eyelid margin. Two types are recognized: 1. Cilium incarnatum internum. 2. Cilium incarnatum externum . Cilium is a neuter noun whose plural is cilia or cilii). Incarnata is the neuter plural of incarnatus, which is the perfect passive participle of incarno, which means "to make or become flesh." Incarnatum is the first supine of incarno. Internum is the adjective neuter form meaning "internal" or "inward." Externum is the adjective neuter form meaning "external" or "outward." The word incarno, from which incarnata and incarnatum are derived imply inflamed, or red and fleshy, as in the Crimson Clover named incarnatum because of its deep crimson color. In the conditions under discussion, there is no inflammation or redness of the eyelid in either of the conditions, and cilium incarnatum internum only causes irritation of the cornea and sometimes a conjunctival inflammation, but no fleshy or inflamed appearance. With that in mind, a more accurate description of these two conditions, derived from the Latin, would be as follows: literally meaning lash growing inward literally meaning lash growing outward.
睫毛在妊娠第22至26周期间由外胚层发育而来。虽然睫毛长度因人而异，但它们不会长到超过一定长度然后自行脱落。通常情况下，除非睫毛过度生长（睫毛过长症），否则一般不需要修剪。如果有人拔掉一根睫毛，大约需要8周才能重新长出来。睫毛不受青春期影响。上睑的睫毛毛囊深度为2.4毫米，下睑为1.4毫米。与下睑相比，上睑有更多活跃的睫毛毛囊（41% 对15%）。睫毛的功能是保护眼睛免受颗粒物侵害。它们也有丰富的神经支配，使其对触摸敏感（被比作猫的胡须），同样有助于保护眼睛。人类下睑有三到四排，75至80根睫毛，而上睑有五到六排，90至160根睫毛分散分布。每根睫毛都有伸出皮肤外的毛干、位于皮肤下的根部以及膨大的末端球部。球部的下部与真皮乳头直接接触，真皮乳头在毛囊周期中带来关键的间充质 - 上皮相互作用。与有表皮、真皮和皮下组织的头皮不同，眼睑皮肤较薄，只有表皮和真皮。睫毛毛囊也没有立毛肌，立毛肌会在寒冷或强烈情绪下使毛发变直。睫毛内翻是指睫毛在皮肤下生长并穿过表面或向后生长到结膜表面，而不是正常地从眼睑边缘长出。可分为两种类型：1. 内翻性倒睫。2. 外倒睫。“cilium”（睫毛）是一个中性名词，其复数形式为“cilia”或“cilii”。“incarnata”是“incarnatus”的中性复数形式，“incarnatus”是“incarno”的完成被动分词，意思是“使或变成肉”。“incarnatum”是“incarno”的第一动形词。“internum”是中性形容词形式，意思是“内部的”或“向内的”。“externum”是中性形容词形式，意思是“外部的”或“向外的”。“incarno”这个词，“incarnata”和“incarnatum”由此派生而来，暗示着发炎，或红色且肉质的，比如绛车轴草因其深红色而被命名为“incarnatum”。在讨论的这些情况中，两种情况的眼睑都没有炎症或发红，内翻性倒睫只会引起角膜刺激，有时还会引起结膜炎症，但没有肉质或发炎的外观。考虑到这一点，从拉丁语派生而来的对这两种情况更准确的描述如下： 字面意思是睫毛向内生长 字面意思是睫毛向外生长 。
