Eye (Final Exam) Flashcards
What is the eyeball (globe) located in?
The orbit
What is another word for the accessory ocular structures? What do they include?
Adnexa.
Palpebrae (eyelids), 3rd eyelid, conjunctiva, lacrimal apparatus
What is the eye composed of?
Lens.
3 layers: 1) Outer fibrous tunic
2) Middle vascular tunic
3) Inner retinal tunic
What is included in the outer fibrous tunic of the eye?
Sclera (white part around eye)
Cornea (clear part at front of eye)
Limbus (corneal-scleral junction)
What is located in the middle vascular tunic of the eye?
Iris
Ciliary Body
Choroid
Iridocorneal Angle (filtration angle, drainage angle; where ciliary body and iris meet)
What is included in the inner retinal layer of the eye?
Pigmented Layer
Neural Layer
(Both = neuroepithelial tunic)
What is the sclera? What is its function?
Posterior portion of the eye, white opaque layer of dense irregular CT
Function: protects the eye, maintains the shape of the eye, provides insertion points for tendons of extraocular muscles
What is the cornea? List some important features.
Anterior portion of the eye.
Avascular, transparent convex-concave lens.
Richly supplied by sensory nerves
Relatively dehydrated to maintain transparency.
Remarkable regenerative capacity.
What are the 5 layers of the cornea?
- Anterior Corneal Epithelium
- Anterior Limiting Lamina/Subepithelial basement membrane - supporting the lining epithelium
- Substantia propria - corneal stroma
- Posterior limiting lamina/membrane - DESCEMET’S MEMBRANE, supporting the endothelium
- Posterior epithelium of cornea - Corneal Endothelium
What are the factors that contribute to corneal transparency?
Avascular
Collagen Arrangement (collagen fibers layered parallel to corneal surface so light can go through)
Proteoglycans between collagen
Na+ pumps to transport water out
What is the limbus? What is its purpose?
The corneoscleral junction
Where the opaque sclera overlaps the transparent cornea - has small blood vessels.
Nutrition for the cornea comes from microvasculature of limbus and aqueous humor.
Region where the transparent cornea merges with the vascular sclera
Epithelium of limbus is continuous with conjunctiva that lines the eyelids
Where does the vitreous humor occupy? Where does the aqueous humor occupy?
Vitreous humor occupies the vitreous space
Aqueous humor occupies the anterior chamber and posterior chamber
What is the iris? What is it composed of?
Stroma - pigmented loose CT, iridial melanin present in stromal cells determines eye colour
Dilator and Sphincter papillae muscles
What is located in the posterior epithelium of the iris in squids and ruminants?
Ridiculous granules (corpora nigra) at the dorsal and ventral pupillary margins
What is the iridocorneal angle? What is it composed of?
At the convergence of the corneoscleral junction (limbus), ciliary body and iris
Composed of pectinate ligament, trabecular mesh work, trabecular (aqueous) veins
Draining point for aqueous humor!
How is eye color determined?
By the amount of pigment in the stroma of the iris. Minimal Pigment (greenish --> blue) More pigment (brown)
What is the ciliary body? What is its function?
Anterior expansion of the choroid at the level of the lens.
Has mechanical and secretory functions (Epithelial cells secrete Aqueous Humor!)
Ciliary Muscle
Ciliary Processes at the base of the iris.
Epithelial Surface - low columnar epithelium (posterior pigmented epithelium of the iris are continuous with nonpigmented epithelium of the ciliary body)
What is ciliary muscle? What does it do? What is it surrounded by?
Smooth muscle.
Contracts during ACCOMODATION (important for focusing on an object), reduces tension of the zonal are fibers of the lens.
Surrounded by loose CT (elastic fibers, vessels, melanocytes)
What are the 2 layers of the epithelial surface of the ciliary body?
2 layers of low columnar epithelium:
1) Non-pigmented - ion transporting forming Aqueous Humor
2) Pigmented - basement membrane extends to form Zonular Fibers that suspend the lens
What suspends the lens?
Zonular Fibers that extend from the basement membrane of the pigmented epithelium of the ciliary body.
What is the aqueous humor? What does it do? What is it formed by?
Occupies anterior and posterior chambers.
Nourishes the cornea (glucose rich)
Maintains intraocular pressure
Formed by non-pigment cells of the ciliary processes
Constant drainage required (at filtration angle)
List the drainage pathway of aqueous humor.
Posterior Chamber –> Through Pupil –> Anterior Chamber –> Iridocorneal Angle –> Past pectinate ligaments –> Scleral Venous Plexus
What is the choroid? What is its function? What are its attachments?
Highly vascularized.
Nutritional source for retina.
Anterior - continuous with stroma of ciliary body
External - Connected to sclera
Internal - Connected to retinal pigmented epithelium
Dorsal - Tapetum Lucidum
What the Tapetum Lucidum? What is its purpose?
Reflective Carpet - shiny eyes of pets in photos
Increases light perception under conditions of poor illumination
Humans/primates don’t have
Only on dorsal part of eye
Regional pigmented epithelium contain little or no pigment where a tapetum lucidum is present.
What are the 3 parts of the retina?
- Sensory/optical part - contacts the choroid
- Non-sensory/ciliary part - inner non-pigmented and outer pigmented ciliary epithelium (pars ciliary retinae)
- Non-sensory/iridal - posterior pigmented epithelium (pas iridica retinae)
What is the retina nourished by?
The vessels of the choroid and by retinal vessels entering via the optic disk.
What is the function of the sensory/optical retina? How is it held in place?
Sends visual images to the brain –> the combined nerve fiber layers converge on the optic disk to form the optic nerve.
Retina has attachment near the optic nerve but otherwise not attached to anything - held in place by vitreous humor.
List the 10 layers of the sensory/optical retina.
Vitreous Body Optic Nerve Fibres Ganglion Cell Layer Inner Plexiform Layer Inner Nuclear Layer Outer Plexiform Layer Cell Bodies of rods and cones Photoreceptor Layer Pigment Cells Choroid
What is the general concept of the optical retina?
Light passes through layers of retina, stimulates photoreceptors cells (rods and cones) - AP generated in photoreceptors cells
Impulse is passed back up to bipolar neurons and then to ganglion cells
Axons of the ganglion cells form nerve fiber layer - these fibers converge at the optic disk (papilla) and leave the eye as the optic nerve
Describe the path of light into the eye.
Tear film –> cornea –> aqueous humor –> pupil –> lens –> vitreous humor –> first 8 layers of retina –> stimulating rods/cones –> absorbed by retinal epithelium
Then visual impulse created passes in reverse order from rods and cones to bipolar cells, ganglion cells and to the optic nerve to the brain.
What is the retinal pigmented epithelium? What is it composed of and what is its function?
Outermost layer of retina.
Consists of flat polygonal cells resting on a basement membrane.
Transport of nutrients and metabolites to the rods and cones, light absorption, phagocytosis
What are rods? What are they composed of and what is their function?
Inner segment of rods is long, thin and straight
Inner segment and outer segment connected through a cilum
Contain flattened membranous disks containing RHODOPSIN (Vitamin A derivative)
Responsible for vision in dim light
2x more abundant in retina than cones
What are cones? What are they composed of and what is their function?
Inner segment of cones has a broad base.
Inner segment and outer segment connected through a cilum.
Disks contain IODOPSIN
Responsible for vision in bright light and color
60 million/retina (half the amount as rods)
What is the vitreous body? What is it composed of and what is its function?
Refractive media.
Occupies space between lens and retina (4/5 of eyeball)
99% water, rich is hyaluronic acid
Gel cortex, liquid center.
Aids in maintaining shape and retinal apposition
What is the lens? What is it surrounded by and what is it composed of?
Entirely surrounded by capsule. Thick on anterior surface.
Anterior epithelium - simple cuboidal cells –> at the equator the elongate and differentiate into lens fibers (prism shaped cells, WITHOUT nuclei that interdigital even extensively and have gap junctions)
There is differentiation and growth of lens throughout life.
Loses vascular supply after development (normal)
What is the eyelid composed of?
Conjunctiva Cilia (eyelashes) Tarsal (Meiboian Glands - sebaceous) Third Eyelid (Nictitating Membrane) Lacrimal (tear) Apparatus - lacrimal glands, lacrimal sac, nasolacrimal gland
What are the 2 types of conjunctiva?
Palpebral Conjunctiva - pink part over vascular submucosa (eg flipped eyelid)
Bulbar Conjunctiva - Covering white part of eye
What is the conjunctiva composed of?
Epithelium is either a pseudostratified columnar or transitional epithelium that becomes stratified squamous near eyelid margin (non-keratinized)
Lots of goblet cells!
What is the third eyelid (nictitating membrane)? What is its function?
Protects eye, removes foreign material.
Corresponds to a fold of the conjunctiva formed by hyaline cartilage in ruminants/dogs, and elastic cartilage in horses/pigs/cats
Lined by conjunctiva.
What is located under the conjunctival surface that can give the surface a “cobblestone” appearance?
Aggregated lymphatic nodles.
What does the gland of the third eyelid do?
Contributes 30-50% of the aqueous portion of the tear film via multiple very small ductules
What does the lacrimal gland do? What are they composed of?
Tear film moistures, lubricates and protects the eye.
Lacrimal glands have tubuloalveolar seromucinous acini composed of secretory cells filled with small granules.
Myoepithelial cells are present at the base.
What are the 3 layers of the tear film?
- Oily Portion - produced by Meibomian (tarsal) glands - superficial layer
- Aqueous Portion - consisting of sero-mucous material produced by the Lacrimal Glands and glands of the third eyelid
- Mucous Portion - produced by Gobet Cells in the conjunctiva
