Cornea
The cornea forms the fibrous layer of the anterior portion of the eye. It functions to refract light entering the eye.
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Summary
- location: anterior one-sixth of the eyeball
- blood supply: avascular
- innervation: long ciliary nerves
- relations: continuous with the sclera posteriorly and covered by the conjunctiva anteriorly
Gross anatomy
Anteriorly, the cornea is a convex structure covered by bulbar conjunctiva. The curvature is greater than that of the rest of the eyeball covered by the sclera. Posteriorly, the cornea is concave and round. It is made up of five layers.
Transparency
Transparency of the cornea is due to the regular arrangement of the collagen fibrils in lamellae in the stroma.
Arterial supply
The cornea is largely avascular. The peripheral parts are related to capillaries from the anterior ciliary arteries. It is nourished by the aqueous humor and gaseous exchange occurs through the tear film.
Lymphatic drainage
The cornea is an alymphatic organ.
Innervation
Densely innervated by the long ciliary nerves, branch of the nasociliary nerve, which is derived from the ophthalmic division of the trigeminal nerve.
Histology
Histologically, the cornea is made up of 5 layers (from superficial to deep):
- epithelium
- Bowman's membrane
- stroma (substantia propria)
- Descemet's membrane
- endothelium
Radiographic features
Imaging of the cornea can be performed by a number of techniques, including:
- corneal topography: characterizes the shape of the cornea qualitatively and quantitatively
- anterior segment optical coherence tomography (AS-OCT): produces a cross-section image of the cornea and other anterior segment structures
- ultrasound biomicroscopy: high-frequency and high resolutions are required
CT and MRI are not performed for imaging of the cornea.
History and etymology
Derived from the Latin cornea tela (“horny tissue”) and from cornu (“horn”).
Related pathology
- astigmatism: refractive error due to aspheric or uneven cornea curvature
- keratoconus: most common corneal ectasia, is a progressive corneal condition characterized by central thinning and steepening of the cornea
- Fuchs endothelial dystrophy: non-inflammatory dystrophy of the cornea
- keratitis
Related Radiopaedia articles
Anatomy: Head and neck
- skeleton of the head and neck
-
cranial vault
- scalp (mnemonic)
- fontanelle
-
sutures
- calvarial
- facial
- frontozygomatic suture
- frontomaxillary suture
- frontolacrimal suture
- frontonasal suture
- temporozygomatic suture
- zygomaticomaxillary suture
- parietotemporal suture (parietomastoid suture)
- occipitotemporal suture (occipitomastoid suture)
- sphenofrontal suture
- sphenozygomatic suture
- spheno-occipital suture (not a true suture)
- lacrimomaxillary suture
- nasomaxillary suture
- internasal suture
- basal/internal
- skull landmarks
- frontal bone
- temporal bone
- parietal bone
- occipital bone
- skull base (foramina)
-
facial bones
- midline single bones
- paired bilateral bones
- cervical spine
- hyoid bone
- laryngeal cartilages
-
cranial vault
- muscles of the head and neck
- muscles of the tongue (mnemonic)
- muscles of mastication
-
muscles of facial expression
- occipitalis muscle
- circumorbital and palpebral muscles
- nasal muscles
- buccolabial muscles
- elevators, retractors and evertors of the upper lip
- levator labii superioris alaeque nasalis muscle
- levator labii superioris muscle
- zygomaticus major muscle
- zygomaticus minor muscle
- malaris muscle
- levator anguli oris muscle
- risorius muscle
- depressors, retractors and evertors of the lower lip
- depressor labii inferioris muscle
- depressor anguli oris muscle
- mentalis muscle
- compound sphincter
- orbicularis oris muscle
- incisivus superior muscle
- incisivus inferior muscle
- muscle of mastication:
- elevators, retractors and evertors of the upper lip
- muscles of the middle ear
- orbital muscles
- muscles of the soft palate
- pharyngeal muscles
- suprahyoid muscles
- infrahyoid muscles
- intrinsic muscles of the larynx
- muscles of the neck
- accessory muscles of the neck
- deep cervical fascia
-
deep spaces of the neck
- anterior cervical space
- buccal space
- carotid space
- danger space
- deep cervical fascia
- infratemporal fossa
- masticator space
- parapharyngeal space
- stylomandibular tunnel
- parotid space
- pharyngeal (superficial) mucosal space
- perivertebral space
- posterior cervical space
- pterygopalatine fossa
- retropharyngeal space
- suprasternal space (of Burns)
- visceral space
- surgical triangles of the neck
- orbit
- ear
- paranasal sinuses
- nose
- oral cavity
- pharynx
- larynx
- viscera of the neck
- blood supply of the head and neck
-
arterial supply
-
common carotid artery
- carotid body
- carotid bifurcation
- subclavian artery
- variants
-
common carotid artery
- venous drainage
-
arterial supply
- innervation of the head and neck
-
cranial nerves
- olfactory nerve (CN I)
- optic nerve (CN II)
- oculomotor nerve (CN III)
- trochlear nerve (CN IV)
-
trigeminal nerve (CN V) (mnemonic)
- trigeminal ganglion
- ophthalmic division
- maxillary division
- mandibular division
- abducens nerve (CN VI)
- facial nerve (CN VII)
-
vestibulocochlear nerve (CN VIII)
- vestibular ganglion (Scarpa's ganglion)
- glossopharyngeal nerve (CN IX)
-
vagus nerve (CN X)
- superior laryngeal nerve
- recurrent laryngeal nerve (inferior laryngeal nerve)
- (spinal) accessory nerve (CN XI)
- hypoglossal nerve (CN XII)
- parasympathetic ganglia of the head and neck
- greater occipital nerve
- third occipital nerve
-
cervical plexus
- muscular branches
- longus capitis
- longus colli
- scalenes
- geniohyoid
- thyrohyoid
-
ansa cervicalis
- omohyoid (superior and inferior bellies separately)
- sternothyroid
- sternohyoid
- phrenic nerve
- contribution to the accessory nerve (CN XI)
- cutaneous branches
- muscular branches
- brachial plexus
- pharyngeal plexus
-
cranial nerves
- lymphatic drainage of the head and neck
- embryological development of the head and neck
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