Anatomy of the Eye

The human eye is a sensory organ whose primary function is vision. They eye has a spheroidal shape and is structured in 3 layers: a supporting outer fibrous layer, a middle vascular layer, and an inner neural layer. The eye can also be subdivided into 3 compartments: the anterior, posterior, and vitreous chambers. Surrounding the eyeball itself are the extraocular muscles, the lacrimal apparatus, various nerves and vessels, and the bony structure of the orbit Orbit The orbit is the cavity of the skull in which the eye and its appendages are situated. The orbit is composed of 7 bones and has a pyramidal shape, with its apex pointed posteromedially. The orbital contents comprise the eye, extraocular muscles, 5 cranial nerves, blood vessels, fat, the lacrimal apparatus, among others. The Orbit and Extraocular Muscles. Light travels through the compartments of the eye to focus on the retina, which is the location where photoreceptors convert the stimulus into a neural impulse that is carried by the optic nerve to the brain.

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Editorial responsibility: Stanley Oiseth, Lindsay Jones, Evelin Maza

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Development

General

  • Develops from the forebrain
  • Regulated by the PAX6 gene
  • Lens placode gives rise to the lens.
  • Optic cup gives rise to the retina.

Timeline

  • Begins at week 3, with formation of optic grooves from forebrain
  • Optic grooves fuse to become the optic vesicles.
  • At week 4, the optic vesicles form the optic cup, which becomes the retina.
  • Continues through week 10 of embryologic development
Embryologic development of the eyes

Embryologic development of the eye

Image by Lecturio.

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Gross Anatomy

General characteristics

The adult eye is a complex organ contained within the orbital cavity (composed of 7 bones). Each eye has multiple layers and chambers and is surrounded by 6 extraocular muscles.

  • Layers of the eye:
    • Fibrous layer: sclera and cornea
    • Vascular layer (the uvea): choroid, ciliary body, and iris
    • Neural layer: retina and optic nerve
  • Chambers of the eye:
    • Anterior: between cornea and iris
    • Posterior: between iris and lens
    • Vitreous: between lens and posterior eye wall
  • Components of the orbit Orbit The orbit is the cavity of the skull in which the eye and its appendages are situated. The orbit is composed of 7 bones and has a pyramidal shape, with its apex pointed posteromedially. The orbital contents comprise the eye, extraocular muscles, 5 cranial nerves, blood vessels, fat, the lacrimal apparatus, among others. The Orbit and Extraocular Muscles:
    • 6 extraocular muscles:
      • Levator palpebrae superioris
      • Superior oblique
      • Inferior oblique
      • Lateral rectus
      • Medial rectus
      • Inferior rectus
    • Lacrimal apparatus:
      • Lacrimal glands and their associated ducts
      • Produce tears to provide lubrication
    • Nerves and blood vessels
  • Function: sense of sight
    • Refractive media directs and refracts light to the retina. Light travels through the:
      • Cornea
      • Lens
      • Aqueous humor
      • Vitreous body
    • Lens and ciliary body adjust the range of accommodation
    • Retina contains photoreceptors (rods and cones) and the optic nerve
Essential anatomy of the eye illustration

Anatomy of the eye

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Layers of the eye

The eye is composed of 3 layers (fibrous, vascular, neural) and a transparent connective tissue Connective tissue Connective tissues originate from embryonic mesenchyme and are present throughout the body except inside the brain and spinal cord. The main function of connective tissues is to provide structural support to organs. Connective tissues consist of cells and an extracellular matrix. Connective Tissue covering (conjunctiva).

Conjunctiva:

  • Loose, transparent connective tissue Connective tissue Connective tissues originate from embryonic mesenchyme and are present throughout the body except inside the brain and spinal cord. The main function of connective tissues is to provide structural support to organs. Connective tissues consist of cells and an extracellular matrix. Connective Tissue that covers the eye (bulbar conjunctiva).
  • Adheres firmly to the limbus of the cornea
  • Reflects back on itself to form the inner layer of the eyelid (palpebral conjunctiva)
  • Highly vascular
  • Maintains normal lubrication of the eye

Fibrous layer:

  • Cornea:
    • Covers anterior aspect of eye
    • Approximately 15% of fibrous layer
    • Transparent, avascular, and richly innervated
    • Responsible for initial refraction of light
  • Sclera:
    • Continuous with cornea
    • Covers posterior aspect of eye
    • > 80% of fibrous layer
    • Seen as the white part of eye
    • Site of attachment for extraocular muscles
  • Limbus:
    • Border between cornea and sclera
    • Pathway of aqueous humor outflow
    • Site of surgical incision for cataract and glaucoma Glaucoma Glaucoma is an optic neuropathy characterized by typical visual field defects and optic nerve atrophy seen as optic disc cupping on examination. The acute form of glaucoma is a medical emergency. Glaucoma is often, but not always, caused by increased intraocular pressure (IOP). Glaucoma surgery

Vascular layer:

  • Uvea, or uveal tract:
    • Composed of the iris, ciliary body, and choroid 
    • Lies between sclera and retina
    • Anterior portion is the iris and ciliary body.
    • Posterior portion is the choroid.
  • Choroid (posterior uvea):
    • Reddish brown layer between the sclera and retina
    • Contains large external vessels and an innermost capillary bed
    • Source of oxygen/nutrients to retina
    • Continuous anteriorly with ciliary body
  • Ciliary body:
    • Muscular structure that connects the choroid with circumference of iris.
    • Alters shape and thickness of lens (accommodation)
    • Ciliary processes secrete aqueous humor.
  • Iris:
    • Pigmented diaphragm Diaphragm The diaphragm is a large, dome-shaped muscle that separates the thoracic cavity from the abdominal cavity. The diaphragm consists of muscle fibers and a large central tendon, which is divided into right and left parts. As the primary muscle of inspiration, the diaphragm contributes 75% of the total inspiratory muscle force. Diaphragm with central aperture ( pupil Pupil The pupil is the space within the eye that permits light to project onto the retina. Anatomically located in front of the lens, the pupil's size is controlled by the surrounding iris. The pupil provides insight into the function of the central and autonomic nervous systems. Physiology and Abnormalities of the Pupil)
    • On anterior surface of lens
    • Sphincter muscles within the iris adjust pupillary size in response to light and the autonomic nervous system Autonomic nervous system The ANS is a component of the peripheral nervous system that uses both afferent (sensory) and efferent (effector) neurons, which control the functioning of the internal organs and involuntary processes via connections with the CNS. The ANS consists of the sympathetic and parasympathetic nervous systems. Autonomic Nervous System.
    • Light exposure/parasympathetic stimulation:
      • Narrows the pupil Pupil The pupil is the space within the eye that permits light to project onto the retina. Anatomically located in front of the lens, the pupil's size is controlled by the surrounding iris. The pupil provides insight into the function of the central and autonomic nervous systems. Physiology and Abnormalities of the Pupil (miosis)
      • Sphincter pupillae muscle
    • Darkness/sympathetic stimulation:
      • Widens the pupil Pupil The pupil is the space within the eye that permits light to project onto the retina. Anatomically located in front of the lens, the pupil's size is controlled by the surrounding iris. The pupil provides insight into the function of the central and autonomic nervous systems. Physiology and Abnormalities of the Pupil (mydriasis)
      • Dilator pupillae muscle
Iris muscle actions

The sphincter muscles of the iris are responsible for constricting (A) and dilating (B) the pupil Pupil The pupil is the space within the eye that permits light to project onto the retina. Anatomically located in front of the lens, the pupil's size is controlled by the surrounding iris. The pupil provides insight into the function of the central and autonomic nervous systems. Physiology and Abnormalities of the Pupil.

Image by Lecturio.

Neural layer:

  • Visual retina:
    • Neural layer:
      • Light-receptive
      • Ends anteriorly along the ora serrata
    • Pigmented cell layer: 
      • Single layer of cells
      • Absorbs light to reduce scattering of light within eye
    • Optic disc or papilla: 
      • Known as the “blind spot”: no photoreceptors
      • Located in the fundus of the retina, which is the location where sensory fibers of the optic nerve enter the eyeball.
    • Macula: 
      • Contains special photoreceptor cones for visual acuity
      • Lacks blood vessels
    • Fovea:
      • Located in center of macula
      • Responsible for high-acuity vision
      • Densely saturated with cone photoreceptors
  • Nonvisual retina:
    • Portion of retina that is not sensitive to light
    • Anterior continuation of the pigment cell layer plus supporting cells over the ciliary body and posterior surface of the iris
Retina

Retina:
The fovea and macula lack blood vessels and are responsible for high-acuity vision. The optic disc is the entrance point for the vasculature of the eye and does not contain photoreceptors.

Image by Lecturio.

Characteristics of the retina and its layers:

Table: Characteristics of the retina and its layers
Layer of the retina (external to internal) Characteristics
Pigment epithelium Epithelium The epithelium is a complex of specialized cellular organizations arranged into sheets and lining cavities and covering the surfaces of the body. The cells exhibit polarity, having an apical and a basal pole. Structures important for the epithelial integrity and function involve the basement membrane, the semipermeable sheet on which the cells rest, and interdigitations, as well as cellular junctions. Surface Epithelium
  • Most external layer, closest to choroid, from which it supplies nutrition to photoreceptors
  • Contains melanin granules and stores vitamin A
  • Absorbs light and prevents reflection
Layer of rods and cones
  • Photoreceptor cells
  • Rods: slender, cylindrical cells containing rhodopsin, located around the fovea centralis, specialized for night vision (dim light) and motion
  • Cones: flask-shaped cells containing photopsin/iodopsin, located within the fovea centralis, specialized for color vision, bright light, object recognition, and visual acuity
External limiting membrane Supports the photoreceptor cells
Outer nuclear membrane Photoreceptors cell nuclei (1st-order neuron)
Outer plexiform layer 1st synapse Synapse The junction between 2 neurons is called a synapse. The synapse allows a neuron to pass an electrical or chemical signal to another neuron or target effector cell. Synapses and Neurotransmission, between cones and rods and bipolar cells
Middle limiting membrane Supporting membrane
Inner nuclear layer Cell bodies and nuclei of bipolar cells (2nd-order neuron), transmit information to ganglion cells
Inner plexiform layer Second synapse Synapse The junction between 2 neurons is called a synapse. The synapse allows a neuron to pass an electrical or chemical signal to another neuron or target effector cell. Synapses and Neurotransmission, between bipolar cells and ganglion cells
Ganglion cell layer
  • Cell bodies and nuclei of ganglion cells (3rd-order neuron) combine here to form the optic nerve (cranial nerve (CN) II).
  • Transmits information to the hypothalamus Hypothalamus The hypothalamus is a collection of various nuclei within the diencephalon in the center of the brain. The hypothalamus plays a vital role in endocrine regulation as the primary regulator of the pituitary gland, and it is the major point of integration between the central nervous and endocrine systems. Hypothalamus, pretectal nucleus, lateral geniculate body, superior colliculus, and visual cortex
Optic nerve fibers Axons of ganglion cells
Internal limiting membrane Most internal layer, closest to the vitreous humor

Chambers of the eye

  • The eye consists of 3 fused chambers:
    • Anterior: between cornea and iris
    • Posterior: between iris and lens
    • Vitreous: between lens and posterior eye wall
  • Aqueous humor:
    • Produced by the ciliary processes of the ciliary body
    • Travels to the anterior and posterior chambers
    • Absorbed via the lymphatics in the Schlemm canal
  • Vitreous body (also known as vitreous humor): 
    • Occupies the vitreous chamber
    • Encased in the vitreous membrane
    • Fluid-like at center and gel-like at edges
    • Attaches firmly to the serrata, optic disc, retinal vessels, lens capsule, and macula
Structure of limbal region

Diagram of the structure of the limbal region:
The aqueous humor is produced by the ciliary processes (1), circulates through the pupil Pupil The pupil is the space within the eye that permits light to project onto the retina. Anatomically located in front of the lens, the pupil's size is controlled by the surrounding iris. The pupil provides insight into the function of the central and autonomic nervous systems. Physiology and Abnormalities of the Pupil of the iris and into the anterior chamber (2), and finally through the Schlemm canal into the scleral venous sinus.

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Neurovasculature

Blood supply

The entire arterial supply of the eye is provided by branches of the ophthalmic artery and drained by a system of veins Veins Veins are tubular collections of cells, which transport deoxygenated blood and waste from the capillary beds back to the heart. Veins are classified into 3 types: small veins/venules, medium veins, and large veins. Each type contains 3 primary layers: tunica intima, tunica media, and tunica adventitia. Veins that unite to form the central vein of the retina.

  • Ophthalmic artery, branch of the internal carotid artery, in turn gives off branches:
    • Central retinal artery:
      • 1st branch of the ophthalmic artery
      • Supplies the inner layer of the retina and all nerve fibers that form the optic nerve
    • Lacrimal artery:
      • 2nd branch of the ophthalmic artery
      • Supplies the eyelids, lacrimal gland, and conjunctiva
    • Ciliary arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries:
      • Include the long and short posterior ciliary arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries and anterior ciliary artery
      • Supply the choroid and iris
    • Supraorbital artery:
      • Bifurcates to form a superficial and deep branch
      • Supplies the upper eyelid, levator palpebrae muscle, skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Structure and Function of the Skin of the forehead and scalp
    • Ethmoidal arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries:
      • Include the anterior and posterior ethmoidal arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries
      • Supply the ethmoid sinuses
    • Medial palpebral artery:
      • Also known as the internal palpebral arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries—superior and inferior
      • Arises from the ophthalmic artery near its terminal branches 
      • Supplies the eyelids
    • Muscular arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries:
      • Medial and lateral branches of the ophthalmic artery
      • Supply the extraocular muscles
    • Terminal branches:
      • Dorsal nasal artery: supplies the lacrimal sac and tip of the nose Nose The nose is the human body's primary organ of smell and functions as part of the upper respiratory system. The nose may be best known for inhaling oxygen and exhaling carbon dioxide, but it also contributes to other important functions, such as tasting. The anatomy of the nose can be divided into the external nose and the nasal cavity. Anatomy of the Nose
      • Supratrochlear artery: supplies the medial forehead
  • Venous drainage: 
    • Central retinal vein and vortex veins Veins Veins are tubular collections of cells, which transport deoxygenated blood and waste from the capillary beds back to the heart. Veins are classified into 3 types: small veins/venules, medium veins, and large veins. Each type contains 3 primary layers: tunica intima, tunica media, and tunica adventitia. Veins merge with superior and inferior ophthalmic veins Veins Veins are tubular collections of cells, which transport deoxygenated blood and waste from the capillary beds back to the heart. Veins are classified into 3 types: small veins/venules, medium veins, and large veins. Each type contains 3 primary layers: tunica intima, tunica media, and tunica adventitia. Veins 
    • These veins Veins Veins are tubular collections of cells, which transport deoxygenated blood and waste from the capillary beds back to the heart. Veins are classified into 3 types: small veins/venules, medium veins, and large veins. Each type contains 3 primary layers: tunica intima, tunica media, and tunica adventitia. Veins drain into the cavernous sinus, pterygoid venous plexus, and facial vein.

Innervation

  • Vision:
    • Optic nerve (CN II)
    • Innermost retinal layer contains photoreceptors that convert light stimuli into neural impulses that are transmitted by the optic nerve:
      • Rods: best in dim light; about 7 million in each retina
      • Cones: color vision; 100 million in each retina
  • Miosis: 
    • Pupillary constriction 
    • Parasympathetic fibers of short ciliary nerves to the constrictor pupillae muscle
  • Mydriasis:
    • Pupillary dilation
    • Sympathetic fibers of long ciliary nerves to the radial dilator pupillae muscle
  • Accommodation:
    • Thickening of the lens to allow for near vision
    • Short ciliary nerves (branch of cranial nerve III) innervate the ciliary muscles, which change the shape of the lens.
  • Sensation: ophthalmic branch (V1) of the cranial nerve V (trigeminal nerve)

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Function

Vision

  • The function of the eye is to provide the sense of sight.
  • Light rays course through the cornea, aqueous humor, pupil Pupil The pupil is the space within the eye that permits light to project onto the retina. Anatomically located in front of the lens, the pupil's size is controlled by the surrounding iris. The pupil provides insight into the function of the central and autonomic nervous systems. Physiology and Abnormalities of the Pupil, lens, and vitreous humor to focus onto the innermost layer of the retina.
  • The cornea and lens work together to focus light onto the retina.
  • The iris adjusts how much light enters the eye by adjusting the size of the pupil Pupil The pupil is the space within the eye that permits light to project onto the retina. Anatomically located in front of the lens, the pupil's size is controlled by the surrounding iris. The pupil provides insight into the function of the central and autonomic nervous systems. Physiology and Abnormalities of the Pupil in response to the intensity of light and the distance of the object.
  • The photoreceptor cells of the retina generate electrical and chemical impulses, which are transmitted to the brain via the optic nerve (CN II), resulting in an interpretation of the image.

Refractive media of the eye

  • Cornea: 
    • Responsible for the majority of refraction
    • Transparent, owing to its collagen arrangement and avascular state 
  • Lens: 
    • Transparent, biconvex
    • Works with cornea for optimal refraction
    • Refraction varies by the amount of accommodation needed:
      • Distant vision: decreased convexity, lens flattens
      • Near vision: increased convexity, lens spherical
  • Vitreous humor (vitreous body): 
    • Watery fluid within transparent jelly-like substance 
    • Maintains intraocular pressure
  • Aqueous humor: 
    • Transparent, watery fluid
    • Protects the cornea and lens and fills the anterior and posterior chambers
    • Produced by the ciliary processes
    • Drains into the scleral venous sinus via the Schlemm canal at the iridocorneal angle

Photoreceptor cells of the retina

  • Rods: 
    • Function best in dim light
    • Provide black-and-white vision
    • 120 million rods in each retina
  • Cones: 
    • Function best in bright light
    • Provide color vision, visual acuity
    • 6 million cones in each retina

Clinical Relevance

Disorders of visual perception

  • Refractive errors Refractive errors By refraction, the light that enters the eye is focused onto a particular point of the retina. The main refractive components of the eye are the cornea and the lens. When the corneal curvature, the refractive power of the lens, does not match the size of the eye, ametropia or a refractive error occurs. Refractive Errors: conditions in which the shape of the eye does not refract light correctly, resulting in blurry vision. The main types of refractive errors are myopia (nearsightedness), hyperopia (farsightedness), presbyopia (loss of near vision with age), and astigmatism (mismatched curves of the cornea and lens).
  • Disorders of the visual pathway Visual pathway The primary visual pathway consists of a relay system, beginning at the retina, whose ganglion cell axons form the optic nerve. The optic nerve fibers from each eye hemidecussate in the optic chiasm (OC), with nasal fibers joining the temporal fibers of the contralateral nerve. Signals are then transmitted to the primary visual cortex of the occipital lobe. The Visual Pathway and Related Disorders: The structures responsible for disorders of the visual pathway Visual pathway The primary visual pathway consists of a relay system, beginning at the retina, whose ganglion cell axons form the optic nerve. The optic nerve fibers from each eye hemidecussate in the optic chiasm (OC), with nasal fibers joining the temporal fibers of the contralateral nerve. Signals are then transmitted to the primary visual cortex of the occipital lobe. The Visual Pathway and Related Disorders include the retina, optic nerve, optic chiasm, optic tract, optic radiation, and visual cortex of the occipital lobe. The site of damage is often localizable by ophthalmoscopy, pupil Pupil The pupil is the space within the eye that permits light to project onto the retina. Anatomically located in front of the lens, the pupil's size is controlled by the surrounding iris. The pupil provides insight into the function of the central and autonomic nervous systems. Physiology and Abnormalities of the Pupil reactions, and the pattern of visual-field defects.

Systemic diseases that affect the eye

  • Diabetic retinopathy: vascular disease of the retina affecting individuals with long-standing diabetes mellitus Diabetes mellitus Diabetes mellitus (DM) is a metabolic disease characterized by hyperglycemia and dysfunction of the regulation of glucose metabolism by insulin. Type 1 DM is diagnosed mostly in children and young adults as the result of autoimmune destruction of β cells in the pancreas and the resulting lack of insulin. Type 2 DM has a significant association with obesity and is characterized by insulin resistance. Diabetes Mellitus. Loss of vision is typically slow and progressive, and it occurs in most individuals 2–3 decades after the onset of diabetes. 
  • Hypertensive retinopathy Hypertensive retinopathy Hypertension has many adverse effects on the eye, of which retinopathy is the most common presentation. Hypertensive retinopathy consists of retinal vascular changes that develop as a direct effect of elevated blood pressure. In acute increases of blood pressure, autoregulation results in retinal arteriolar narrowing. Hypertensive Retinopathy: retinal changes in individuals with long-standing hypertension. Hypertensive retinopathy Hypertensive retinopathy Hypertension has many adverse effects on the eye, of which retinopathy is the most common presentation. Hypertensive retinopathy consists of retinal vascular changes that develop as a direct effect of elevated blood pressure. In acute increases of blood pressure, autoregulation results in retinal arteriolar narrowing. Hypertensive Retinopathy usually includes arterial narrowing and hemorrhage.

Miscellaneous disorders of the eye

  • Conjunctivitis Conjunctivitis Conjunctivitis is a common inflammation of the bulbar and/or palpebral conjunctiva. It can be classified into infectious (mostly viral) and noninfectious conjunctivitis, which includes allergic causes. Patients commonly present with red eyes, increased tearing, burning, foreign body sensation, and photophobia. Conjunctivitis: inflammation Inflammation Inflammation is a complex set of responses to infection and injury involving leukocytes as the principal cellular mediators in the body's defense against pathogenic organisms. Inflammation is also seen as a response to tissue injury in the process of wound healing. The 5 cardinal signs of inflammation are pain, heat, redness, swelling, and loss of function. Inflammation of the conjunctiva due to an infectious (including bacterial, viral, or fungal agents), allergic, or autoimmune reaction. Individuals present with conjunctival hyperemia, eye discharge that may be watery or purulent, discomfort, or a foreign-body sensation. 
  • Retinal detachment Retinal detachment Retinal detachment is the separation of the neurosensory retina from the retinal pigmented epithelium and choroid. Rhegmatogenous retinal detachment, the most common type, stems from a break in the retina, allowing fluid to accumulate in the subretinal space. Retinal Detachment: medical emergency in which a layer of retinal tissue peels off from the underlying supporting choroid layer. Retinal detachment Retinal detachment Retinal detachment is the separation of the neurosensory retina from the retinal pigmented epithelium and choroid. Rhegmatogenous retinal detachment, the most common type, stems from a break in the retina, allowing fluid to accumulate in the subretinal space. Retinal Detachment may be due to trauma or a high degree of myopia, and individuals often have a family history of this disorder. Retinal detachment Retinal detachment Retinal detachment is the separation of the neurosensory retina from the retinal pigmented epithelium and choroid. Rhegmatogenous retinal detachment, the most common type, stems from a break in the retina, allowing fluid to accumulate in the subretinal space. Retinal Detachment should be treated within 24–48 hours or it can lead to permanent loss of vision.
  • Cataracts: decrease in vision due to a cloudiness or loss of transparency of the lens, common in advancing age. Treatment of cataracts requires surgical extraction of the opaque lens and, in most cases, implantation of a new lens.
  • Glaucoma: condition of increased pressure within the eye as a result of inadequate drainage of aqueous humor, usually due to a blockage. Unless medically treated or surgically corrected, glaucoma Glaucoma Glaucoma is an optic neuropathy characterized by typical visual field defects and optic nerve atrophy seen as optic disc cupping on examination. The acute form of glaucoma is a medical emergency. Glaucoma is often, but not always, caused by increased intraocular pressure (IOP). Glaucoma can lead to gradual vision loss owing to damage to the optic nerve. 
  • Horner syndrome Horner syndrome Horner syndrome is a condition resulting from an interruption of the sympathetic innervation of the eyes. The syndrome is usually idiopathic but can be directly caused by head and neck trauma, cerebrovascular disease, or a tumor of the CNS. Horner Syndrome: This syndrome is caused by disruption of the sympathetic nerve supply to the eye and is characterized by ipsilateral miosis, partial ptosis, enophthalmos, and hemifacial anhidrosis.
  • Retinoblastoma Retinoblastoma Retinoblastoma is a rare tumor but the most common primary intraocular malignancy of childhood. It is believed that the condition arises from a neuronal progenitor cell. Retinoblastoma can be heritable or nonheritable. Retinoblastoma: intraocular malignancy that begins in the retina. Retinoblastoma Retinoblastoma Retinoblastoma is a rare tumor but the most common primary intraocular malignancy of childhood. It is believed that the condition arises from a neuronal progenitor cell. Retinoblastoma can be heritable or nonheritable. Retinoblastoma typically manifests during childhood with an abnormal pupillary reflex to light, known as leukocoria (white pupil Pupil The pupil is the space within the eye that permits light to project onto the retina. Anatomically located in front of the lens, the pupil's size is controlled by the surrounding iris. The pupil provides insight into the function of the central and autonomic nervous systems. Physiology and Abnormalities of the Pupil).

References

  1. Bales, T.R., Lopez, M.J., Clark, J. (2021). Embryology, eye. StatPearls. https://www.ncbi.nlm.nih.gov/books/NBK538480/
  2. Silverman, M.A., Brenner, B.E. (2021). What is the conjunctiva and what is its function? Medscape. https://www.medscape.com/answers/797874-22279/what-is-the-conjunctiva-and-what-is-its-function
  3. Nguyen, J.D., Duong, H. (2021). Anatomy, head and neck, eye nerves. StatPearls. https://www.ncbi.nlm.nih.gov/books/NBK549919/
  4. Bird, B., Stawicki, S.P. (2021). Anatomy, head and neck, ophthalmic arteries. StatPearls. https://www.ncbi.nlm.nih.gov/books/NBK482317/
  5. Dahl, A.A., Gest, T.R. (2017). Retina anatomy. Medscape. https://emedicine.medscape.com/article/2019624-overview
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  9. Smith, A.M., Czyz, C.N. (2020). Neuroanatomy, cranial nerve 2 (optic). StatPearls. https://www.ncbi.nlm.nih.gov/books/NBK507907/

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