{"id":3064,"date":"2020-12-13T21:28:09","date_gmt":"2020-12-13T19:28:09","guid":{"rendered":"https:\/\/meddists.com\/learn\/pre-clinical\/histology\/neurohistology\/eyes-eyelids\/external-layer\/"},"modified":"2021-12-04T11:16:15","modified_gmt":"2021-12-04T09:16:15","slug":"external-layer","status":"publish","type":"page","link":"https:\/\/meddists.com\/learn\/pre-clinical\/histology\/nervous-system\/eyes-eyelids\/external-layer\/","title":{"rendered":"External Layer"},"content":{"rendered":"\n<figure class=\"wp-block-image size-large is-resized\"><a href=\"https:\/\/meddists.com\/learn\/wp-content\/uploads\/2021\/12\/external-eye.png\" target=\"_blank\" title=\"External Layer\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/meddists.com\/learn\/wp-content\/uploads\/2021\/12\/external-eye-1024x768.png\" alt=\"\" class=\"wp-image-8746\" width=\"840\" height=\"630\" srcset=\"https:\/\/meddists.com\/learn\/wp-content\/uploads\/2021\/12\/external-eye-1024x768.png 1024w, https:\/\/meddists.com\/learn\/wp-content\/uploads\/2021\/12\/external-eye-300x225.png 300w, https:\/\/meddists.com\/learn\/wp-content\/uploads\/2021\/12\/external-eye-768x576.png 768w, https:\/\/meddists.com\/learn\/wp-content\/uploads\/2021\/12\/external-eye.png 1186w\" sizes=\"auto, (max-width: 840px) 100vw, 840px\" \/><\/a><figcaption><strong>Figure 1. Section of the eye showing the external and middle portions of the eye.<\/strong><\/figcaption><\/figure>\n\n\n<span class=\"block-heading\" id=\"header_1\">\n<h3 class=\"wp-block-heading\" class=\"wp-block-heading\" class=\"title_collection title1\">Cornea<\/h3>\n<\/span><span class=\"block-content\" id=\"contents_1\">\n\n\n<div class=\"wp-block-columns is-layout-flex wp-container-core-columns-is-layout-8f761849 wp-block-columns-is-layout-flex\">\n<div class=\"wp-block-column is-vertically-aligned-top is-layout-flow wp-block-column-is-layout-flow\" style=\"flex-basis:66.66%\">\n<p class=\"wp-block-paragraph\">The cornea consists of 5 layers, formed by cells and connective tissue (stroma), from the outside-inside:<\/p>\n\n\n\n<ol class=\"wp-block-list\"><li>Epithelium<\/li><li>Bowman&#8217;s membrane<\/li><li>Stroma<\/li><li>Descemet&#8217;s membrane<\/li><li>Endothelium<\/li><\/ol>\n<\/div>\n\n\n\n<div class=\"wp-block-column is-layout-flow wp-block-column-is-layout-flow\" style=\"flex-basis:33.33%\">\n<figure class=\"wp-block-image size-medium\"><a href=\"https:\/\/meddists.com\/learn\/wp-content\/uploads\/2021\/12\/cornea-histology.png\" target=\"_blank\" title=\"External Layer\"><img loading=\"lazy\" decoding=\"async\" width=\"300\" height=\"108\" src=\"https:\/\/meddists.com\/learn\/wp-content\/uploads\/2021\/12\/cornea-histology-300x108.png\" alt=\"\" class=\"wp-image-8751\" srcset=\"https:\/\/meddists.com\/learn\/wp-content\/uploads\/2021\/12\/cornea-histology-300x108.png 300w, https:\/\/meddists.com\/learn\/wp-content\/uploads\/2021\/12\/cornea-histology-1024x369.png 1024w, https:\/\/meddists.com\/learn\/wp-content\/uploads\/2021\/12\/cornea-histology-768x277.png 768w, https:\/\/meddists.com\/learn\/wp-content\/uploads\/2021\/12\/cornea-histology.png 1183w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption><strong>Figure 2. Histology section of the cornea (a), drawing of the upper layers including the epithelium, Bowman&#8217;s membrane, and upper stroma (b).<\/strong><\/figcaption><\/figure>\n<\/div>\n<\/div>\n\n\n<\/span><span class=\"block-heading\" id=\"header_2\">\n<h3 class=\"wp-block-heading\" class=\"wp-block-heading\" class=\"title_collection title1\">Sclera<\/h3>\n<\/span><span class=\"block-content\" id=\"contents_2\">\n\n\n<ul class=\"wp-block-list\"><li>The &#8220;white of the eye&#8221;<\/li><li>Consists of <strong>dense irregular connective tissue<\/strong><\/li><li>From the outside, the external (&#8220;visible&#8221;) part of the sclera is covered by the delicate epithelium of the <strong>bulbar conjunctiva<\/strong><\/li><\/ul>\n\n\n<\/span><span class=\"block-heading\" id=\"header_3\">\n<h4 class=\"wp-block-heading\" class=\"wp-block-heading\" class=\"title_collection title2\">Parts of the sclera<\/h4>\n<\/span><span class=\"block-content\" id=\"contents_3\">\n\n\n<p class=\"wp-block-paragraph\">The sclera can be divided into three parts, from superficial to deep:<\/p>\n\n\n\n<ol class=\"wp-block-list\"><li><strong>Episclera<\/strong><ul><li>The external layer<\/li><\/ul><\/li><li><strong>Substancia propria<\/strong><ul><li>Also known as the sclera proper (also known as Tenon&#8217;s capsule)<\/li><li>Where the tendons of the ocular muscles attach<\/li><\/ul><\/li><li><strong>Suprachoroid lamina<\/strong><ul><li>Contains many resident connective tissue cells (macrophages, fibroblasts)<\/li><\/ul><\/li><\/ol>\n\n\n\n<p class=\"wp-block-paragraph\">Between the episclera and substancia propria, we can find the <strong>episcleral space&nbsp;<\/strong>(<strong>Tenon&#8217;s&nbsp;space<\/strong>) which allows the eye to rotate freely within the orbit.<\/p>\n\n\n<\/span><span class=\"block-heading\" id=\"header_4\">\n<h4 class=\"wp-block-heading\" class=\"wp-block-heading\" class=\"title_collection title2\">Cornocleral limbus (&#8220;limbus region&#8221;)<\/h4>\n<\/span><span class=\"block-content\" id=\"contents_4\">\n\n\n<p class=\"wp-block-paragraph\">The junction between the cornea and sclera.<\/p>\n\n\n\n<ul class=\"wp-block-list\"><li>Do not forget that the external sclera is covered by the bulbar conjunctiva<\/li><li>The location where Bowman&#8217;s membrane ends and the uppermost epithelium thickens up to 12 layers near the conjunctiva, with both corneal and conjunctival epithelial cells<\/li><\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">The <strong>iridocorneal angle<\/strong> which is located at the limbus is an important landmark due to the presence of the <strong>canal of Schlemm<\/strong> which is formed by a series of channels forming a trabecular meshwork &#8212; the <strong>spaces of Fontana<\/strong>, that allow the outflow of the aqueous humor.<\/p>\n\n\n\n<div class=\"wp-block-image\"><figure class=\"aligncenter\"><a href=\"https:\/\/meddists.com\/wp-content\/uploads\/2019\/02\/flow1.png\" target=\"_blank\" title=\"External Layer\"><img decoding=\"async\" src=\"https:\/\/meddists.com\/wp-content\/uploads\/2019\/02\/flow1-600x450.png\" alt=\"\" class=\"wp-image-8917\"\/><\/a><figcaption><strong>Figure 3. Flow within the chambers of the eye<\/strong><\/figcaption><\/figure><\/div>\n\n\n<\/span><span class=\"block-heading\" id=\"header_5\">\n<h3 class=\"wp-block-heading\" class=\"wp-block-heading\" class=\"title_collection title1\">References<\/h3>\n<\/span><span class=\"block-content\" id=\"contents_5\">\n\n\n<ol class=\"wp-block-list\"><li><strong>Figure 1, 3.<\/strong> Blausen.com staff (2014). CC BY-SA 4.0<\/li><li><strong>Figure 2.<\/strong> Peterson JL, Ceresa BP. Epidermal Growth Factor Receptor Expression in the Corneal Epithelium.&nbsp;<em>Cells<\/em>. 2021; 10(9):2409. https:\/\/doi.org\/10.3390\/cells10092409, CC BY<\/li><\/ol>\n<\/span><div id=\"the_titles\" style=\"display:none;\"><h3 class=\"wp-block-heading\" class=\"wp-block-heading\">Cornea<\/h3><h3 class=\"wp-block-heading\" class=\"wp-block-heading\">Sclera<\/h3><h4 class=\"wp-block-heading\" class=\"wp-block-heading\">Parts of the sclera<\/h4><h4 class=\"wp-block-heading\" class=\"wp-block-heading\">Cornocleral limbus (&#8220;limbus region&#8221;)<\/h4><h3 class=\"wp-block-heading\" class=\"wp-block-heading\">References<\/h3><\/div>","protected":false},"excerpt":{"rendered":"<p>Cornea The cornea consists of 5 layers, formed by cells and connective tissue (stroma), from the outside-inside: Epithelium Bowman&#8217;s membrane Stroma Descemet&#8217;s membrane Endothelium Sclera The &#8220;white of the eye&#8221; Consists of dense irregular connective tissue From the outside, the external (&#8220;visible&#8221;) part of the sclera is covered by the delicate epithelium of the bulbar [&hellip;]<\/p>\n","protected":false},"author":23,"featured_media":0,"parent":3033,"menu_order":1,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-3064","page","type-page","status-publish","hentry"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v28.0 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>External Layer &#8211; Meddists<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/meddists.com\/learn\/pre-clinical\/histology\/nervous-system\/eyes-eyelids\/external-layer\/\" \/>\n<meta name=\"twitter:label1\" content=\"Est. reading time\" \/>\n\t<meta name=\"twitter:data1\" content=\"2 minutes\" \/>\n<script type=\"application\/ld+json\" class=\"yoast-schema-graph\">{\"@context\":\"https:\\\/\\\/schema.org\",\"@graph\":[{\"@type\":\"WebPage\",\"@id\":\"https:\\\/\\\/meddists.com\\\/learn\\\/pre-clinical\\\/histology\\\/nervous-system\\\/eyes-eyelids\\\/external-layer\\\/\",\"url\":\"https:\\\/\\\/meddists.com\\\/learn\\\/pre-clinical\\\/histology\\\/nervous-system\\\/eyes-eyelids\\\/external-layer\\\/\",\"name\":\"External Layer &#8211; Meddists\",\"isPartOf\":{\"@id\":\"https:\\\/\\\/meddists.com\\\/learn\\\/#website\"},\"primaryImageOfPage\":{\"@id\":\"https:\\\/\\\/meddists.com\\\/learn\\\/pre-clinical\\\/histology\\\/nervous-system\\\/eyes-eyelids\\\/external-layer\\\/#primaryimage\"},\"image\":{\"@id\":\"https:\\\/\\\/meddists.com\\\/learn\\\/pre-clinical\\\/histology\\\/nervous-system\\\/eyes-eyelids\\\/external-layer\\\/#primaryimage\"},\"thumbnailUrl\":\"https:\\\/\\\/meddists.com\\\/learn\\\/wp-content\\\/uploads\\\/2021\\\/12\\\/external-eye-1024x768.png\",\"datePublished\":\"2020-12-13T19:28:09+00:00\",\"dateModified\":\"2021-12-04T09:16:15+00:00\",\"breadcrumb\":{\"@id\":\"https:\\\/\\\/meddists.com\\\/learn\\\/pre-clinical\\\/histology\\\/nervous-system\\\/eyes-eyelids\\\/external-layer\\\/#breadcrumb\"},\"inLanguage\":\"en-US\",\"potentialAction\":[{\"@type\":\"ReadAction\",\"target\":[\"https:\\\/\\\/meddists.com\\\/learn\\\/pre-clinical\\\/histology\\\/nervous-system\\\/eyes-eyelids\\\/external-layer\\\/\"]}]},{\"@type\":\"ImageObject\",\"inLanguage\":\"en-US\",\"@id\":\"https:\\\/\\\/meddists.com\\\/learn\\\/pre-clinical\\\/histology\\\/nervous-system\\\/eyes-eyelids\\\/external-layer\\\/#primaryimage\",\"url\":\"https:\\\/\\\/meddists.com\\\/learn\\\/wp-content\\\/uploads\\\/2021\\\/12\\\/external-eye.png\",\"contentUrl\":\"https:\\\/\\\/meddists.com\\\/learn\\\/wp-content\\\/uploads\\\/2021\\\/12\\\/external-eye.png\",\"width\":1186,\"height\":889},{\"@type\":\"BreadcrumbList\",\"@id\":\"https:\\\/\\\/meddists.com\\\/learn\\\/pre-clinical\\\/histology\\\/nervous-system\\\/eyes-eyelids\\\/external-layer\\\/#breadcrumb\",\"itemListElement\":[{\"@type\":\"ListItem\",\"position\":1,\"name\":\"Home\",\"item\":\"http:\\\/\\\/meddists.com\\\/learn\\\/\"},{\"@type\":\"ListItem\",\"position\":2,\"name\":\"Pre-clinical\",\"item\":\"https:\\\/\\\/meddists.com\\\/learn\\\/pre-clinical\\\/\"},{\"@type\":\"ListItem\",\"position\":3,\"name\":\"Histology\",\"item\":\"https:\\\/\\\/meddists.com\\\/learn\\\/pre-clinical\\\/histology\\\/\"},{\"@type\":\"ListItem\",\"position\":4,\"name\":\"Nervous system\",\"item\":\"https:\\\/\\\/meddists.com\\\/learn\\\/pre-clinical\\\/histology\\\/nervous-system\\\/\"},{\"@type\":\"ListItem\",\"position\":5,\"name\":\"Eyes &#038; Eyelids\",\"item\":\"https:\\\/\\\/meddists.com\\\/learn\\\/pre-clinical\\\/histology\\\/nervous-system\\\/eyes-eyelids\\\/\"},{\"@type\":\"ListItem\",\"position\":6,\"name\":\"External Layer\"}]},{\"@type\":\"WebSite\",\"@id\":\"https:\\\/\\\/meddists.com\\\/learn\\\/#website\",\"url\":\"https:\\\/\\\/meddists.com\\\/learn\\\/\",\"name\":\"Meddists\",\"description\":\"Let&#039;s Get Studying\",\"potentialAction\":[{\"@type\":\"SearchAction\",\"target\":{\"@type\":\"EntryPoint\",\"urlTemplate\":\"https:\\\/\\\/meddists.com\\\/learn\\\/?s={search_term_string}\"},\"query-input\":{\"@type\":\"PropertyValueSpecification\",\"valueRequired\":true,\"valueName\":\"search_term_string\"}}],\"inLanguage\":\"en-US\"}]}<\/script>\n<!-- \/ Yoast SEO plugin. -->","yoast_head_json":{"title":"External Layer &#8211; Meddists","robots":{"index":"index","follow":"follow","max-snippet":"max-snippet:-1","max-image-preview":"max-image-preview:large","max-video-preview":"max-video-preview:-1"},"canonical":"https:\/\/meddists.com\/learn\/pre-clinical\/histology\/nervous-system\/eyes-eyelids\/external-layer\/","twitter_misc":{"Est. reading time":"2 minutes"},"schema":{"@context":"https:\/\/schema.org","@graph":[{"@type":"WebPage","@id":"https:\/\/meddists.com\/learn\/pre-clinical\/histology\/nervous-system\/eyes-eyelids\/external-layer\/","url":"https:\/\/meddists.com\/learn\/pre-clinical\/histology\/nervous-system\/eyes-eyelids\/external-layer\/","name":"External Layer &#8211; Meddists","isPartOf":{"@id":"https:\/\/meddists.com\/learn\/#website"},"primaryImageOfPage":{"@id":"https:\/\/meddists.com\/learn\/pre-clinical\/histology\/nervous-system\/eyes-eyelids\/external-layer\/#primaryimage"},"image":{"@id":"https:\/\/meddists.com\/learn\/pre-clinical\/histology\/nervous-system\/eyes-eyelids\/external-layer\/#primaryimage"},"thumbnailUrl":"https:\/\/meddists.com\/learn\/wp-content\/uploads\/2021\/12\/external-eye-1024x768.png","datePublished":"2020-12-13T19:28:09+00:00","dateModified":"2021-12-04T09:16:15+00:00","breadcrumb":{"@id":"https:\/\/meddists.com\/learn\/pre-clinical\/histology\/nervous-system\/eyes-eyelids\/external-layer\/#breadcrumb"},"inLanguage":"en-US","potentialAction":[{"@type":"ReadAction","target":["https:\/\/meddists.com\/learn\/pre-clinical\/histology\/nervous-system\/eyes-eyelids\/external-layer\/"]}]},{"@type":"ImageObject","inLanguage":"en-US","@id":"https:\/\/meddists.com\/learn\/pre-clinical\/histology\/nervous-system\/eyes-eyelids\/external-layer\/#primaryimage","url":"https:\/\/meddists.com\/learn\/wp-content\/uploads\/2021\/12\/external-eye.png","contentUrl":"https:\/\/meddists.com\/learn\/wp-content\/uploads\/2021\/12\/external-eye.png","width":1186,"height":889},{"@type":"BreadcrumbList","@id":"https:\/\/meddists.com\/learn\/pre-clinical\/histology\/nervous-system\/eyes-eyelids\/external-layer\/#breadcrumb","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"http:\/\/meddists.com\/learn\/"},{"@type":"ListItem","position":2,"name":"Pre-clinical","item":"https:\/\/meddists.com\/learn\/pre-clinical\/"},{"@type":"ListItem","position":3,"name":"Histology","item":"https:\/\/meddists.com\/learn\/pre-clinical\/histology\/"},{"@type":"ListItem","position":4,"name":"Nervous system","item":"https:\/\/meddists.com\/learn\/pre-clinical\/histology\/nervous-system\/"},{"@type":"ListItem","position":5,"name":"Eyes &#038; Eyelids","item":"https:\/\/meddists.com\/learn\/pre-clinical\/histology\/nervous-system\/eyes-eyelids\/"},{"@type":"ListItem","position":6,"name":"External Layer"}]},{"@type":"WebSite","@id":"https:\/\/meddists.com\/learn\/#website","url":"https:\/\/meddists.com\/learn\/","name":"Meddists","description":"Let&#039;s Get Studying","potentialAction":[{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https:\/\/meddists.com\/learn\/?s={search_term_string}"},"query-input":{"@type":"PropertyValueSpecification","valueRequired":true,"valueName":"search_term_string"}}],"inLanguage":"en-US"}]}},"_links":{"self":[{"href":"https:\/\/meddists.com\/learn\/wp-json\/wp\/v2\/pages\/3064","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/meddists.com\/learn\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/meddists.com\/learn\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/meddists.com\/learn\/wp-json\/wp\/v2\/users\/23"}],"replies":[{"embeddable":true,"href":"https:\/\/meddists.com\/learn\/wp-json\/wp\/v2\/comments?post=3064"}],"version-history":[{"count":10,"href":"https:\/\/meddists.com\/learn\/wp-json\/wp\/v2\/pages\/3064\/revisions"}],"predecessor-version":[{"id":8761,"href":"https:\/\/meddists.com\/learn\/wp-json\/wp\/v2\/pages\/3064\/revisions\/8761"}],"up":[{"embeddable":true,"href":"https:\/\/meddists.com\/learn\/wp-json\/wp\/v2\/pages\/3033"}],"wp:attachment":[{"href":"https:\/\/meddists.com\/learn\/wp-json\/wp\/v2\/media?parent=3064"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}