Eye I Flashcards
What are the accessory structures of the eye?
- Eyelid
- Conjunctiva
- Lacrimal Gland
What is the function of the eyelid?
Protect eyeball
Prevent evaporation of tears when closed
Distribute tear film across surface of eyeball
Maintain moisture
What are the characteristics of the eyelid?
Thin skin externally
Palpebral conjunctiva internally
Orbicularis oculi - skeletal muscle that closes the eye
Tarsal plates - skeleton of eyelid
What are the tarsal plates of the eyelid?
Provide structural support of eyelid
What are the glands of the eyelid?
Glands of Zeis - Sebaceous glands of eyelashes
Glands of Moll - modified apocrine glands of eyelashes that open into eyelash follicles
Tarsal (Meibomian) glands
What is the function of the Tarsal (Meiobomian) glands of the eyelid?
Modified sebaceous glands within the tarsal plates
Open onto free edge of the lid
Oily secretion slows the evaporation
What occurs when there is a blockage to the Tarsal (Meibomian) glands?
Chalazion which is inflammation of the tarsal gland
What is a bacterial infection of the sebaceous glands of eyelashes (Glands of Zeis)?
Stye
What is the function of the conjunctiva?
Maintain moisture, provide lubrication between eyeball and eyelid
What are the parts of the conjunctiva?
Bulbar - covers sclera
Palpebral - covers inside of eyelid
Stratified columnar epithelium with goblet cells - mucous secretion of goblet cells lubricate and protect anterior aspect of the eye
Continuous with corneal epithelium - transition to stratified squamous at corneosclera limbus and continuous with corneal epithelium
What is the function of the lacrimal gland?
Maintain moisture
Removal of foreign materials
What is the structure of the lacrimal gland and what does it contain?
Compound tubuloacinar gland that secretes lacrimal fluid (tears)
Lacrimal fluid (tears) - sterile, composed mostly of water, contains lysozyme (antibacterial agent).
Maintains hydration of eyeball, flush irritants from surface of eyeball
What is the structure of lacrimal canaliculi?
Stratified squamous
What is the structure of lacrimal sac?
Pseudostratified ciliated columnar
What is the structure of nasolacrimal duct?
Pseudostratified ciliated columnar
What is flow of lacrimal fluid?
Produced by lacrimal gland
Secreted onto eyeball by lacrimal ducts
Flow medially across the surface of the eyeball
Collected by the lacrimal canaliculi (lined with stratified squamous epithelium)
Canaliculi drain into the lacrimal sac - lacrimal sac lined by pseudostratified ciliated columnar epithelium
Lacrimal sac drains into nasolacrimal duct - lined by pseudostratified ciliated columnar epithelium
Nasolacrima duct drains into nasal cavity
What is pseudostratified ciliated columnar epithelium considered?
Respiratory epithelium
What is the anterior segment of the eye and what does it contain?
Anterior to lens and ciliary body and filled with aqueous humor. Contains anterior and posterior chamber.
Contains:
Cornea
Anterior sclera
Iris
Pupil
Ciliary body and muscle
Aqueous humor = aqueous fluid
What is the anterior chamber?
Anterior to the iris
What is the posterior chamber?
Posterior to the iris
What is the posterior segment of the eye and what does it contain?
Posterior to the lens and ciliary body and filled with vitreous humor
Contains:
Posterior sclera
Choroid
Retina
Vitreous body
What is vitreous humor?
Transparent gel made of mainly water, but also contains collagen, hyaluronic acid, and hyalocytes.
What are hyalocytes?
Vitreous cells
Function as macrophages and synthesize hyaluronic acid
What are the layers of the eye and what is it divided up into?
Fibrous layer - most external layer of the eye and divided into sclera and cornea
Vascular layer - divided into iris, ciliary body, and choroid
Retina - divided into retinal pigment epithelium (RPE) and neural retina
What are the characteristics of the Lens? What is its function?
Biconvex, transparent and very elastic
Avascular
No innervation
Layers include lens capsule, subscapular epithelium, and lens fibers
Function is to focus light rays on the retina
What is the structure of the lens capsule?
Basement membrane/basal lamina of the subscapular epithelial cells
What is the structure of the subscapular epithelium?
Cuboidal layer of cells
Only present on the anterior surface of the lens
Differentiate into lens fibers near the equator of the lens
What is the structure of the lens fibers?
Subscapular epithelial cells differentiate into lens fibers
Near equator of lens
Produced throughout life, rate decreases with age
Mature fibers lose nuclei and acquire crystallins (lens proteins)
Fibers stiffen and enlarge with age
What are the function of crystallins within lens fibers?
Proteins that increase refractor index of lens fibers
What is cataracts?
Loss of transparency of the lens
What can occur when lens fibers stiffen and enlarge with age?
Leads to presbyopia
Age related farsightedness related to loss of accomodation
What is the structure and function of the sclera?
Posterior 5/6 of the eyeball
White of the eye
Tough fibrous connective tissue (collagen and elastic fibers)
Extraocular muscles insert on the sclera
Pierced by the optic nerve, blood vessels, and other nerves
Function is to maintain the shape of the eyeball
What is the structure and function of the cornea?
Anterior 1/6 of the eyeball
Continuous with the sclera
Transparent and avascular
Highly innervated
Main site of light refraction in the eye
Six layers
What is the corneoscleral limbus?
Junction of cornea and sclera
Transition from highly vascularized sclera to avascular cornea
Transitions from stratified columnar epithelium to stratified squamous corneal epithelium
Trabecular meshwork (Spaces of Fontana)
Scleral venous sinus (Canal of Schlemm)
What is the structure and function of the trabecular meshwork or Spaces of Fontana of the corneoscleral limbus?
Channels combine to form the scleral venous sinus
Drains aqueous humor from anterior chamber
What is the structure and function of the scleral venous sinus or Canal of Schlemm of the corneoscleral limbus?
Drains aqueous humor into aqueous veins in sclera
Apparatus for outflow of aqueous humor
What is the flow of aqueous humor?
Aqueous humor produced by ciliary epithelium
Secreted into posterior chamber
Flows into anterior chamber into the pupil
Drains through trabecular meshwork
Drains into scleral venous sinus to network of scleral veins
What are the six layers of the cornea from external to internal?
Epithelium
Bowman’s membrane
Stroma
Pre-Descemet Layer
Descemet’s membrane
Endothelium
What is the structure and function of the epithelium of the cornea?
Continuous with bulbar conjunctiva
Non-keratinized stratified squamous
Cells replaced every 7 days
Richly innervated
Cells have microvilli to help retain tears and prevent drying
What is the structure and function of Bowman’s Membrane of the Cornea?
Acellular and does not regenerate
Ends at corneoscleral limbus
Contributes to strength and stability of cornea
Acts as barrier to infection
What is the structure and function of the stroma of the cornea?
Most of corneal thickeness - substantia propria
Parallel collagen fibrils organized into lamellae
Precise orientation of lamellae maintain transparency of cornea
Corneal fibroblasts interspersed between lamellae to help with repair process
What is the structure and function of Pre-Descemet Layer of the cornea?
Protects cornea from damage
Thin, tough collagenous membrane
Rupture leads to aqueous fluid leaking into cornea
What is the structure and function of Descemet’s membrane?
Basal lamina of corneal endothelium
Secreted and maintained by corneal endothelial cells
Thickens with age
Helps maintain corneal curvature
What is the structure and function of the endothelium of the cornea?
Faces anterior chamber of the eye
Simple squamous epithelium
Removes excess fluid from corneal stroma to maintain transparency
What is the structure and function of the iris?
Muscular diaphragm anterior to the lens
Controls size of the pupil and amount of light that contacts retina
Melanocytes in stroma and pigment epithelium of iris bock passage of light in the eyes
Stroma
Pupil
What is the structure and function of the pupil?
Central aperture of the iris
Sphincter pupillae - constricts pupil, innervated by parasympathetics
Dilator pupillae - Dilates pupil, sympathetic innervation
What is the structure and function of the stroma of the iris?
Vascularized loose CT
Contains melanocytes - determine eye color
Sphincter pupillae
What is the structure and function of pigment epithelium?
2 rows of cuboidal cells
Function is to block light rays
Posterior row adjacent to posterior chamber
Anterior row is myoepithelium
Basal surface is dilator pupillae muscle
What is the structure and function of the ciliary body?
Ciliary Muscle + Ciliary Processes
Ciliary muscle - sphincter muscle, parasympathetic innervation, responsible for accomodation
Ciliary processes - zonular fibers (suspensory ligaments), lined with ciliary epithelium that secretes zonular fibers and aqueous humor
What is accomodation?
Contraction of ciliary muscle relaxes suspensory ligament allowing lens to round for near vision
Relaxation of ciliary muscles puts tension on suspensory ligament flattening lens for far vision
What is the structure and function of the ciliary epithelium?
Double layer of cuboidal cells
Only outer layer pigmented and continuous with the retinal pigment epithelium and nonphotosensitive retina
Inner layer is non pigemented and produces aqueous humor and secretes zonular fibers
What is the structure and function of the choroid?
Between retina and sclera
Heavily pigmented and vascularized - absorbs light that has passed through retina and prevents reflection
Provides blood to outer layers of retina
2 layers:
Choriocapillary layer - inner vascular layer with fenestrated blood vessels, and provides nutrients to outer layers via the opthalamic artery
Bruch’s membrane - thin hyaline membrane, innermost, attached to first layer of retina
What is glaucoma?
Increase in intraocular pressure due to an increase in volume of aqueous humor - either due to overproduction or impeded drainage
Sustained increase in pressure can prevent flow to eye
2 types:
Open angle glaucoma - drainage of aqueous humor slowed by blockage of trabecular meshwork , iridocorneal angle is open
Closed angle - closing of iridocorneal angle limits or obstructs drainage of aqueous humor
