The Eye Flashcards
What are the components of the eyeball?
- a lens
- 3 layers: outer fibrous tunic, middle vascular tunic, and inner retinal tunic
What is the Adnexa?
- accessory ocular structure
- palpebrae (eyelids), third eyelid and conjunctive, and the lacrimal apparatus
What are the components of the fibrous tunic?
- sclera
- cornea
- limbus
Describe the Sclera and its functions
- posterior portion of the eye
- white opaque layer of dense irregular CT
- protects the eye
- maintains shape of the eye
- provides insertion points for tendons of extraocular muscles
Describe the Cornea
- anterior portion of the eye
- avascular, transparent, concave-conves lens
- has regenerative capacity
- has 5 layers
What are the layers of the Cornea?
1) anterior corneal epithelium
2) anterior basement membrane
3) substantia propria = stroma
4) posterior basement membrane
5) posterior corneal epithelium - endothelium
What type of epithelium lines the anterior and posterior surface of the Cornea?
anterior: stratified squamous
posterior: simple squamous
What factors contribute to the transparency of the Cornea?
- avascular
- collagen arrangement (parallel to corneal surface)
- proteoglycans between collagen
- Na+ pumps to transport water out
Describe the Limbus
- corneoscleral junction
- small blood vessels
- epithelium is continuous with the conjunctive that lines the eyelids
What is the Vascular tunic composed of?
- iris
- iridocorneal angle
- ciliary body
- choroid
Describe the Iris
- pigmented loose CT
- melanin in stromal cells determines color
- dilator and sphinctor pupillae muscles
- separates posterier and anterior chambers
- posterior epithelium (corpora nigra present in horses and ruminants)
Describe the Iridocorneal angle
- at convergence of Limbus, ciliary body, and iris
- pectinate ligament
- trabecular meshwork
- trabecular veins
- draining point for aqueous humor
What is the Ciliary Body?
anterior expansion of the choroid at the level of the lens
What is the ciliary muscle and what is its function?
- smooth muscle
- surrounded by loose CT
- very vascular
- contracts and reduces tension of zonular fibers of the lens
What are the two layers of the ciliary processes, and what is their function?
pigmented layer: forms zonular fibers to suspend the lens
nonpigmented layer: forms aqueous humor
What are the functions of aqueous humor?
- nourishes cornea
- maintains intraocular pressure
What is the pathway of aqueous humor drainage?
posterior chamber > through pupil > anterior chamber > iridocorneal angle > past pectinate ligaments > scleral venus plexus
Describe the Choroid
- highly vascular
- nutritional source for retina
- anterior: continuous with ciliary body
- external: connected to sclera
- internal: connected to retinal pigmented epithelium
- dorsal: tapetum lucidum
What is the tapetum lucidum?
- part of the choroid
- increases light perception under conditions of poor ilumination
- reflects light
What are the parts of the Neuro-Epithelial/Retinal tunic?
- sensory/optical part: contacts choroid
- nonsensory/ciliary part: contacts ciliary body
- iridal part: posterior pigmented epithelium
Describe the Sensory/Optical Retina
- sends visual images to brain
- held in place by vitreous body
- nerve fibers converge to form optic nerve
- has many layers
What is the path of light through the eye?
through tear film, cornea, aqueous humor, pupil, lens, vitreous humor, first 8 layers of retina, stimulates rods or cones, then absorbed by retinal epithelium
What is the path of the visual impulse?
- light stimulates photoreceptor cells
- impulse passed to bipolar neurons, then to ganglion cells
- axons of ganglion cells form nerve fiber layer, and leave eye as optic nerve
Describe the retinal pigmented epithelium
- outermost layer of retina
- flat polygonal cells resting on a basement membrane
- transport of nutrients and metabolites to the photoreceptor cells, light absorption, and phagocytosis
Describe the rod photoreceptor cells
- inner segment is long and thin
- contains flattened, membranous disks containing pigment Rhodopsin
- responsible for vision in dim light
Describe the cone photoreceptor cells
- inner segment has a broad base
- contains flattened, membranous disks containing pigment Iodopsin
- responsible for vision in bright light, and color vision
Describe the Vitreous Body
- occupies space between lens and retina
- 99% water, rich in hyaluronic acid
- gelatinous, colorless, viscous fluid
- aids in maintaining shape and retinal apposition
Describe the Lens
- entirely surrounded by capsule
- anterior epithelium of simple cuboidal cells
- epithelial cells will elongate and differentiate to form lens fibers
- lens fibers lack nuclei, grow throughout life
- lens is suspended by zonular fibers
- loses vascular supply after development
What are the components of the eyelid?
- conjunctiva
- cilia (eyelashes)
- tarsal (Meibomian) glands
- third eyelid
- lacrimal apparatus
Describe the conjunctiva
- CT lined by epithelium
- transitional or pseudostratified columnar that becomes stratified squamous
- has goblet cells
- palpebral: inner surface of lid
- bulbar: against eyeball
Describe the third eyelid
- protects eye, removes foreign material
- lined by conjunctiva
- aggregated lymph nodules located under conjunctival surface
- gland of 3rd eyelide produces aqueous portion of tear film
Describe the Lacrimal gland
- have tubuloalveolar seromucinous acini composed of secretory cells filled with small granules
- myoepithelial cells
