Eye Flashcards
What is in the aqueous chamber?
Anterior chamber, posterior chamber, aqueous humor
What is in the vitreous chamber?
Region posterior to lens, contains vitreous body that fills the cavity
What are the three concentric tunics of the eye?
Fibrous tunic, uvea/vascular tunic, retinal tunic
What is in the fibrous tunic?
Sclera, cornea
What is in the uvea/fibrous tunic?
Choroid, ciliary body, iris
What is in the retinal tunic?
Outer pigmented layer, inner neural layer
What is the cornea?
Transparent structure, lacks blood vessels and lymph, highly sensitive with rich nerve supply
What clinical correlate is special regarding the cornea?
Easy for transplant with little risk of rejection by hosts immune system due to lack of blood vessels and lymphatics
How does the cornea retain moistness from tear film?
Microvilli
What are the 5 layers of the cornea?
Corneal epithelium
Bowmans membrane
Stroma
Descemets membrane
Corneal endothelium
What is the corneal epithelium lined with?
Stratified squamous non keratinized
What are cells attached by in corneal epithelium?
Desmosomes
What do the nuclei of the corneal epithelium contain?
Ferritin, iron storage protein, protects corneal DNA from free radical damage from UV light
What does the corneal epithelium have a rich supply of that trigger blinking reflex?
Free nerve endings
What is the limbus or corenosclera junction?
Site when the sclera becomes the cornea, epithelium continues with the conjunctiva epithelium that covers the sclera
How do minor injuries of the cornea heal rapidly?
Migration of the cells from limbus junction
Where are hemidesmosomes present in the cornea?
Between basal layer of cells and the underlying basal lamina
How is the basal lamina of cornea attached to underlying stroma?
Anchoring fibrils
Anchoring filaments
Anchoring plaques
Keratin filaments
What is the corneal bowmans membrane?
Layer of dense accumulation of interwoven collagen fibrils, connective tissue, *free of cells
Can the bowmans membrane regenerate?
No, if damaged, vison will be impaired
When does the bowmans membrane end?
Ends at corneosclera junction limbus
What is the function of the bowmans membrane?
Provides support to the epithelium, acts as a barrier to spread of infections
What is the corneal stroma/substantia propria?
Thin lamellae consisting of parallel bundles of collagen fibrils, type 1 and 5 collagen.
Devoid of blood vessels or lymphatics
Between lamellae are sheets of slender fibroblasts called keratocytes
What is function of keratocytes in corneal stroma?
Produce extracellular ground substance which contains lumican and keratocan
What does type 5 collagen and ground substance do for the corneal stroma?
Regulate the precise diameter and spacing of the collagen fibrils
Where is the corneal stroma derived from?
Neural crest
What is the descemets membrane ?
Type 4 collagen, represents basal lamina to endothelial cells, PAS positive stain
What does the descemets membrane separate in the cornea?
The corneal endothelium from the adjacent stroma
What does the descemets membrane extend to be, peripherally beneath sclera meshwork?
Pectinate ligament
What does pectinate ligament do for the cornea?
Helps maintain normal curvature of cornea
What is the cornea endothelium?
Single layer of squamous cells, covers corneal surface that faces the anterior chamber
What are cells attached by in the corneal endothelium?
Zonula adherents
Zonula occludens
Desmosomes
What do the cells of corneal endothelium contain?
Mitochondria, vesicles, rER and golgi, Na/K ATPase pumps on lateral plasmalemma
What is the sclera made up of?
Dense connective tissue, scattered fibroblasts, fine network of elastic fibers and ground substance
What are the three layers of the sclera?
Episclera
Sclera Proper
Lamina Fusca/Suprachoroid lamina
What is the episclera layer of the sclera?
External layer, loose connective tissue
What is the sclera proper of sclera called?
Tennons capsule
What is the sclera proper/tennons capsule?
Dense network of thick collagen fibers, dense collagen
What is the lamina fusca/suprachoroid lamina of the sclera?
Thin collagen fibers, melanocytes, elastic fibers
Adjacent to choroid
What does the conjunctiva cover?
Anterior part of sclera and lines the eyelids
When does the avascular cornea stroma transition abruptly to a well vascularized stroma, and corneal collagen fibers merge with those of the sclera?
Corneoscleral junction/limbus
Where are the descemets membrane and its simple endothelium replaced with the trabecular meshwork?
At the corneosclera junction/limbus
What does the trabecular meshwork merge to form a larger space of in the scleral venous sinus?
Canal of Schlemm
What is aqueous humor produced by?
Ciliary processes
What is process of aqueous humor drainage?
Aqueous humor leaves ciliary processes and passes through the posterior chamber to get to the anterior chamber, where it passes through the trabecular meshwork into the canal of Schlemm, fluid then enters collecting veins in the sclera
What is glaucoma caused by?
Hindrance of drainage of aqueous humor from anterior chamber, can be caused by obstruction of the trabecular meshwork or obstruction of canal of schlemm
What are the two types of glaucoma?
Primary open angle
Acute angle closure/closed angle
What is primary open angle glaucoma?
Slow process, drainage channels and canal of schlemm get blocked
What is acute angle closure/closed angle glaucoma?
Serious with sudden onset of vision loss
Occurs when the iridocorneal angle is more narrow than usual, this obstructs the aqueous humor drainage at the trabecular meshwork
What does the middle uveal tunic form?
Forms the pigmented vascularized tunic of the eye, three parts: iris, ciliary body, choroid
What is the iris?
Arises from the anterior border of the ciliary body, forms a contractile diaphragm, has a central aperture called the Pupil
What does the anterior surface of the iris consist of?
Matted layer of interdigitating fibroblasts and melanocytes, marked with ridges and grooves due to this, no epithelium, exposed to aqueous humor in anterior chamber
What does the posterior surface of the iris consist of?
Double layer of pigmented cells: anterior and posterior
What does the anterior pigmented epithelium of the posterior surface of iris consist of?
Contractile myoepithelial cells, less heavily pigmented, comprise the dilator pupillae muscle
What is the dilator pupillae muscle supplied with?
Sympathetic nerves
What does the posterior pigmented epithelium of the posterior surface of iris consist of?
Basal lamina faces the posterior chamber, very rich in melanin granules that protects the interior eye from an excess of light, continuation of the pigment layer of the ciliary epithelium
What is the intermediate core of the iris?
Thick core of heavily vascularized connective tissue stroma, contains the sphincter pupillae muscle
What is the sphincter pupillae muscle supplied with?
Parasympathetic nerves
What is the Ora Serrata?
Marks the anterior limit of retina and choroid
What are the radial ridges of the anterior third of the ciliary body called?
Ciliary processes
What does the ciliary body stroma consist of?
Two layers:
Outer- smooth muscle called ciliary muscle, contraction changed the shape of the lens
Inner- vascular layer, extends into ciliary processes
What is the epithelium of the ciliary body?
Double layer of low columnar pigmented and non pigmented epithelial cells
Where is the epithelium of ciliary body derived from?
Two layers of optic cup
The epithelial cells directly covering the stroma of the ciliary body contain lots of?
Melanin, corresponds to the anterior projection of the pigmented retina epithelium
The surface layer of epithelial cells of the ciliary body lack?
Melanin, continuous with the sensory layer of the retina
What are the functions of ciliary process epithelium?
Secretion of aqueous humor
Secretion and anchoring of zonular fibers, forms suspensory ligaments of lens
Major component of blood aqueous barrier
What junctional complexes does the blood aqueous barrier have?
Tight junctions between non pigmented epithelial cells
Where are the zonular fibers produced from?
Non pigmented cells of the epithelium in ciliary process
What is role of zonular fibers?
Anchors the lens in the center of ciliary body
What do zonular fibers attach to?
The fibrous ECM of the lens capsule
What does the choroid consist of?
Loose, well vascularized connective tissue, numerous melanocytes
What is the role of melanocytes in the choroid?
Prevent light from entering eye except through the pupil
What are the two layers of the choroid?
Choroidocapillary lamina/Vascular layer
Bruch membrane
What is the choroidocapillary lamina/vascular layer of choroid?
Rich microvasculature- important for nutrition to the outer retinal layers
Melanocytes
What is the bruch membrane of the choroid?
Acellular, collagen and elastic fibers, thin extracellular sheet between vascular layer and pigment layer of retina
Where is the inner tunic derived from?
Inner and outer layer of optic cup
What does the retinal pigment layer of the inner tunic attach to?
Attach to bruch membrane and choroidocapillary lamina of choroid
What does neural retina layer of inner tunic consist of?
Inner layer, stratified layer with neurons and photoreceptors
What does the retinal pigment layer of the inner tunic consist of?
Outer layer, simple cuboidal, junctional complexes, gap junctions, basal folds with associated mitochondria
What do the apical ends of the cells in retinal pigment epithelium extend?
Projections and processes that surround the tips of photoreceptors rods and cones and provides support
What do the processes in retinal pigment epithelium consist of?
Melanin granules, lysosomes, perioxisomes, and abundant sER
What does the sER of retinal pigment epithelium specialize in?
Retinal vitamin A isomerization, and supply it to photoreceptors
What is the function of the retinal pigment epithelium?
Absorption of scattered light that passes through neural layer
Tight junctions contribute to form blood retina barrier
Restoration of photosensitivity to visual pigments that were dissociated in response to light
Phagocytosis and degradation of shed components
Removal of free radicals and secretion of GH
What does the blood retina barrier do?
Isolated the retina photoreceptors from the highly vascularized choroid, regulates transport of ions between the two compartments
What does the neural retina layer consist of?
9 distinct layers
What does outer nuclear layer contain?
Cell bodies of photoreceptors
What does inner nuclear layer contain?
Nuclei of bipolar cells, amacrine cells, horizontal cells
What does ganglionic layer contain?
Neurons with long axons-Ganglion cells
What layer do the ganglion cells make up?
Nerve fiber layer and converge to form the optic nerve
What does the outer plexiform layer contain?
Axons of photoreceptors, dendrites of associated neurons in INL
What does the inner plexiform layer contain?
Axons of connecting neurons in the INL, dendrites of the ganglion cells
What does the rod and cone layer contain?
Polarized neurons, photosensitive portions aligned in the retinas rod and cone layer
What is the muller cell?
Elongated glial cell, processes extend and span the entire thickness of neural retina
What are the functions of the muller cell?
Maintain ionic environment
Provide neurotrophic substances
Remove waste products
Regulate water and ion homeostasis
Regulate blood flow
Form an inter blood retina barrier
What are the two boundaries of muller cells?
Outer limiting layer, inner limiting membrane
What is the outer limiting layer of muller cells?
Forms a well defined adherent junctions between muller cell and photoreceptor cells
What is the inner limiting membrane of muller cells?
Terminal expansion of muller cell processes, cover the collagenous membrane of vitreous body, form the inner surface of the retina
What is the ganglion cell layer?
Cell bodies of large multipolar nerve cells, nissl bodies
What does the axon of ganglion cell do?
Passes through nerve fiber layer and then into optic nerve
What do some ganglion cells serve as?
Nonvisual photoreceptors- detect changes in light quality and quantity during each 24 hour cycle, signals pass via axons of the retinohypothalamic tract to pineal gland, pineal gland secretes melatonin- helps establish bodies circadian rhythm
What does the nerve fiber layer contain?
Axons from ganglion cells
What are rod cells?
Extremely sensitive to light, function in low light
Secrete rhodopsin
What is inner segment of rod cell?
Synthesizes rhodopsin, glycogen, mitochondira, polyribosomes
What is outer segment of rod cell?
Flattened membranous discs, storage space for rhodopsin, initiates the visual stimulus
What are cone cells?
Less sensitive to light, sensitive to bright light, essential for visual acuity and color vision, most sensitive to green blue and red
What is inner segment of cone cell?
Synthesizes iodopsin
What is outer segment of cone cell?
Stacked membranous continuous invaginations of plasma membrane , stores iodopsin
What is fovea centralis?
Most acute and sharpest vision, very precise visual acuity
What does fovea centralis consist of?
Cell bodies of ganglionic and inner nuclear layers are dispersed peripherally, only cone cells in this region, devoid of conducting neurons and capillaries
What is macula lutea?
Yellow rim fat deposition surrounding fovea centralis
What is optic disc?
Blind spot, where the axons converge to form optic nerve, nerve fibers originate in ganglionic cell layer
What is the lamina cribrosa/cribriform plate?
The region of the sclera that contains the openings where the nerve fibers transverse through the sclera
What does the lens do?
Focuses light onto retina
What does lens contain?
Avascular tissue, highly elastic
Three principal components: Lens capsule, subscapular lens epithelium, lens fibers
What is the lens capsule?
Composed of type 4 collagen and proteoglycans, provides attachment to ciliary zonular fibers
Where is lens capsule derived from?
Basement membrane of embryonic lens vesicle
What is the subscapular lens epithelium?
Single layer of cuboidal cells, present only on anterior surface of lens, epithelial cells divide and provide new cells at the equator, differentiate as lens fibers, allows the lens to grow at equator
What are the lens fibers?
Terminally differentiated epithelial cells, cytoplasm becomes filled with proteins crystallin, organelles undergo autophagy, fibers are tightly packed together to form a transparent tissue specialized for light refraction
What is lens held in place by?
Ciliary zonular fibers
What does ciliary zonule fibers provide?
Process of visual accommodation, permit focusing near and far objects by changing curvature of lens
What are the two portions of the eyelid?
Outer cutaneous portion, inner conjunctival portion
What is outer cutaneous portion of eyelid lined with?
Stratified squamous keratinized, overlying loose connective tissue dermis and skeletal muscle orbicularis oculi
What is inner conjunctival portion of eyelid lined with?
Thin mucus membrane, then conjunctiva
What are the tarsal glands?
Sebaceous glands, holocrine section, produces oily layer on the surface of tear film that retards the evaporation of normal tear layer
What are the glands of Zeis?
Modified sebaceous glands connected with and empty their secretion onto follicles of eyelashes
What are glands of moll?
Modified apocrine sweat glands that secrete lipid that adds to the superficial layer of tear film
What are the lacrimal glands?
Tubuloacinar serous glands with myoepithelial cells, produce tears with accessory lacrimal glands
What do tears do for conjunctiva?
Keep the surface of conjunctiva and cornea moist and rinse of dust, tears protect the corneal epithelium and contain antibacterial and UV protective agents
What does blinking result in?
Gentle compression of the lacrimal gland and release fluid
What is lacrimal canaliculi lined with?
Stratified squamous epithelium
What is lacrimal sac and nasolacrimal duct lined with?
Pseudostratified columnar ciliated epithelium
What are the tears secreted by?
Lacrimal glands
Accessory lacrimal glands
Goblet cells of conjunctiva
Tarsal glands of the eyelid
What proteins does the tear contain?
Tear albumin
Lactoferrin
Lysozyme
Immunoglobulin A
Mucins
What is the conjunctiva?
Thin transparent mucosa, covers the exposed anterior portion of the sclera and continues as lining on inner surface of eyelids
What is conjunctiva lined with?
Stratified columnar epithelium cells with numerous mucus secreting goblet cells (Palpebral conjunctiva)
When does the conjunctiva become stratified squamous with goblet cells?
At the corneal rim (Bulbar conjunctiva)
