[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Anatomy](https://durgical.com/en/anatomy/) › [Head and neck](https://durgical.com/en/anatomy/region/head-and-neck/) › Cornea [Sense organs](https://durgical.com/en/anatomy/system/sense-organs/) · [Head and neck](https://durgical.com/en/anatomy/region/head-and-neck/) # Cornea The cornea is the clear dome at the front of the eye; it does about two thirds of the eye's focusing and is the part reshaped by laser eye surgery. [See in 3D →](https://durgical.app/?from=durgipedia&lang=en#region=head_neck&select=cornea&side=r) Opens in the Durgical app, no sign-up needed. ## What it is The clear dome at the front of the eye. ## What it does Does about two thirds of the eye's focusing; LASIK reshapes it. ## Key points - Five classic layers from front to back: epithelium, Bowman layer, stroma (most of its thickness), Descemet membrane and endothelium (some texts add a pre-Descemet layer) - Clarity depends on the endothelial pump keeping the stroma dehydrated; endothelial cells do not regenerate, so their loss leads to corneal oedema - Corneal reflex: afferent V1 (nasociliary nerve), efferent [facial nerve (VII)](https://durgical.com/en/anatomy/facial-nerve/) to [orbicularis oculi](https://durgical.com/en/anatomy/orbital-part-of-orbicularis-oculi/); touching one cornea makes both eyes blink - Having no vessels gives corneal grafts a lower rejection rate than most other tissue transplants ## Key facts **Where** Front sixth of the outer coat of the eye **Blood supply** Avascular: aqueous humour, tears, limbal vessels **Nerve** V1 (long ciliary nerves): corneal reflex **Function** Two thirds of the eye's focusing power (~43 D) ## Relations **In front** Tear film, and the [eyelids](https://durgical.com/en/anatomy/superior-tarsus/) when the eye is closed **Behind** [Anterior chamber](https://durgical.com/en/anatomy/anterior-chamber-of-eyeball/) and its aqueous humour, which feeds the endothelium; the [iris](https://durgical.com/en/anatomy/iris/) lies behind, across the chamber **Contents** Fine branches of the long ciliary nerves (V1), which lose their myelin as they enter so the stroma stays clear; no blood or lymph vessels ## How to find it The clear dome in front of the iris; its edge is the limbus, where it meets the [sclera](https://durgical.com/en/anatomy/sclera/) and the conjunctiva and where corneal stem cells live. Under the slit lamp each layer can be told apart in a thin optical section. ## Examination - Corneal reflex with a wisp of cotton: no blink in either eye points to a V1 lesion on the touched side; a blink only in the other eye points to a facial nerve lesion on the touched side - Fluorescein staining under blue light: abrasions and ulcers glow green; a branching (dendritic) pattern suggests herpes simplex keratitis - Seidel test: leaking aqueous washes out concentrated fluorescein, revealing a full-thickness wound ## On imaging Corneal topography and tomography map curvature and thickness (keratoconus shows focal, often inferior, steepening and thinning); pachymetry measures thickness; specular microscopy counts endothelial cells. ## Common problems - Refractive errors (short- or long-sightedness, astigmatism) come partly from its curve. - Scratches and ulcers (contact- [lens](https://durgical.com/en/anatomy/lens/) wearers are at risk): pain, redness, light sensitivity. - Keratoconus: the cornea thins and bulges into a cone. ## How it is diagnosed Slit-lamp exam, a dye that shows scratches, and corneal maps (topography) before laser surgery. ## Treatment - Glasses or contact lenses. - Laser reshaping of the cornea (LASIK and similar). - Antibiotic drops for ulcers; corneal cross-linking for keratoconus; a corneal transplant for scarring. ## Clinical notes - Thin corneas make tonometry read falsely low and thick ones falsely high, so thickness is measured when assessing glaucoma - Kayser–Fleischer ring: a golden-brown ring of copper in Descemet membrane at the periphery, a sign of Wilson disease - Arcus: a grey-white lipid ring just inside the limbus; common in older people, it may point to hyperlipidaemia in the young - Fuchs endothelial dystrophy: gradual endothelial loss with blurred vision worse on waking; it can be treated by transplanting only the endothelial layer - Laser refractive surgery reshapes the stroma, either under a cut flap or after removing the epithelium; a thin or irregular cornea rules it out ## Development The epithelium comes from surface ectoderm; the stroma and endothelium come from neural crest cells. ## Memory aid Layers from front to back: Every Boy Should Do Exercise (Epithelium, Bowman, Stroma, Descemet, Endothelium). ## Related conditions - [Hurler syndrome (mucopolysaccharidosis type I)](https://durgical.com/en/conditions/hurler-syndrome/) - [Morquio syndrome (mucopolysaccharidosis type IV)](https://durgical.com/en/conditions/morquio-syndrome/) - [Xeroderma pigmentosum](https://durgical.com/en/conditions/xeroderma-pigmentosum/) - [Vitamin A deficiency (night blindness and xerophthalmia)](https://durgical.com/en/conditions/vitamin-a-deficiency/) - [Wilson disease](https://durgical.com/en/conditions/wilson-disease/) - [Free-living amoeba infections (Naegleria meningoencephalitis, Acanthamoeba)](https://durgical.com/en/conditions/free-living-amoeba-infections/) - [Onchocerciasis (river blindness)](https://durgical.com/en/conditions/onchocerciasis/) - [Chemical eye injury](https://durgical.com/en/conditions/chemical-eye-injury/) - [Corneal abrasion and ocular foreign body](https://durgical.com/en/conditions/corneal-abrasion-and-ocular-foreign-body/) - [Keratitis and corneal ulcer](https://durgical.com/en/conditions/keratitis-and-corneal-ulcer/) - [Herpes zoster ophthalmicus](https://durgical.com/en/conditions/herpes-zoster-ophthalmicus/) - [Ocular trauma: hyphema and open globe injury](https://durgical.com/en/conditions/ocular-trauma-hyphema-and-open-globe-injury/) - [Refractive errors and presbyopia](https://durgical.com/en/conditions/refractive-errors-and-presbyopia/) - [Trachoma](https://durgical.com/en/conditions/trachoma/) - [Pterygium](https://durgical.com/en/conditions/pterygium/) - [Dry eye disease](https://durgical.com/en/conditions/dry-eye-disease/) - [Graves disease (hyperthyroidism)](https://durgical.com/en/conditions/graves-disease/) - [Open-angle glaucoma](https://durgical.com/en/conditions/open-angle-glaucoma/) - [Acute angle-closure glaucoma](https://durgical.com/en/conditions/acute-angle-closure-glaucoma/) - [Conjunctivitis](https://durgical.com/en/conditions/conjunctivitis/) ## Test yourself Think of the answer, then tap the question to see it. ## What are the five classic layers of the cornea from front to back? Epithelium, Bowman layer, stroma, Descemet membrane and endothelium; the stroma makes up most of the thickness. ## What keeps the cornea clear, and why does endothelial loss cause corneal oedema? The endothelial pump keeps the stroma dehydrated; endothelial cells do not regenerate, so their loss lets the stroma swell. ## What are the afferent and efferent limbs of the corneal reflex? Afferent: V1 (nasociliary nerve); efferent: facial nerve (VII) to orbicularis oculi. Touching one cornea makes both eyes blink. ## What is a Kayser–Fleischer ring and what does it indicate? A golden-brown ring of copper in Descemet membrane at the corneal periphery: a sign of Wilson disease. ## Why is corneal thickness measured when assessing glaucoma? Thin corneas make tonometry read falsely low and thick corneas falsely high. [Add to my cards (5)](https://durgical.app/estudiar/?add=/en/anatomy/cornea/) Educational information, not medical advice. For any symptom, see a health professional. ## Its names **Official Latin (TA2)** cornea TA2 6744 **Official Spanish (DeCS)** Córnea DeCS D003315 **English (TA2)** Cornea ## Related - [Anterior chamber](https://durgical.com/en/anatomy/anterior-chamber-of-eyeball/) Sources: Terminologia Anatomica (TA2); [DeCS](https://decs.bvsalud.org/es/ths/resource/?id=3333); [Anatomy, Head and Neck, Eye Cornea](https://www.ncbi.nlm.nih.gov/books/NBK470340/); [Keratoconus](https://www.ncbi.nlm.nih.gov/books/NBK470435/). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/anatomy/cornea/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/anatomy/cornea/