Lecture 23: Eye Flashcards
The eyeball (globe) is in a socket called the
orbit
Eye is composed of
- A lens
- Outer fibrous tunic
- Middle vascular tunic
- Inner retinal tunic
Adnexa
accessory ocular structures
Adnexa include
- Palpebrae (eyelids)
- Third eyelid and conjuctiva
- Lacrimal apparatus
Fibrous tunic includes
- Sclera
- Cornea
Vascular tunic includes
- Iris
- Ciliary body
- Choroid
Retina includes
- Pigmented layer
- Neural layer
Sclera
- Posterior portion of eye
- White opaque layer of dense irregular CT
Functions of sclera
- Protects the eye
- Maintains the shape of eye
- Provides insertion points for tendons of extraocular muscles
Cornea
- Anterior portion of the eye
- Avascular, transparent convex-concave lens
Cornea is supplied by what nerve
opthalmic branch of Cr N V
Cornea water content
dehydrated to maintain transparency
Regenerative capacity of cornea
High
5 layers of 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
4 factors contributing to corneal transparency
- Avascular
- Collagen arrangement
- Proteoglycans between collagen
- Na+ pumps to transport water out
Limbus of cornea
- Corneoscleral junction
- Where the opaque sclera overlaps the transparent cornea. This area has small blood vessels
Nutrition for the cornea comes from
microvasculature of limbus and aqueous humor
The epithelium of the limbus is continuous with
the conjunctiva that lines the eyes
Vascular tunic is composed of
- Iridocorneal angle
- Iris
- Ciliary body
- Choroid
Stroma of the iris
-Pigmented loose CT
What determines eye color
Iridial melanin present in the stromal cells in the iris
What muscles are in the iris
dilator and sphincter pupillae muscles
Posterior epithelium of the iris - equids and ruminants
Iridic granules (corpora nigra) are present at the dorsal and ventral pupillary margins
Iridocorneal angle location
At the convergence of the corneoscleral junction (limbus), and iris
Iridocorneal angle is composed of
- Pectinate ligament
- Trabecular meshwork
- Trabecular (aqueous) veins
Iridocorneal angle function
draining point of aqueous humor
Ciliary body
Anterior expansion of the choroid at the level of the lens
Ciliary muscle
- Smooth
- Contracts during accommodation, reduces tension of zonular fibers of the lens
- Surrounded by loose CT (elastic fibers, vessels, melanocytes)
Ciliary processes are located
at the base of the iris
Epithelial surface of ciliary body
- 2 layers of low columnar epithelium
- Inner pigmented - basement membrane extends to form zonular fibers that suspend the lens
- Outer nonpigmented - ion transporting forming aqueous humor
Aqueous humor occupies
anterior and posterior chambers
Purpose of aqueous humor
- Nourishes the cornea (glucose rich)
- Maintains intraocular pressure
Aqueous humor is formed by
non-pigmented cells of ciliary processes
How often does the aqueous humor need to be drained?
Constantly
Drainage pathway o the aqueous humor
- Posterior chamber
- Through pupil
- Anterior chamber
- Iridocorneal angle
- Past pectinate ligaments
- Scleral venous plexus
What is the nutritional source of the retina
Choroid
Anterior choroid
Continuous with stroma of ciliary body
External choroid
Connected to the sclera
Internal choroid
Connected to retinal pigmented epithelium
Dorsal choroid
Tapetum lucidum
Choroid is _____ vascularized
highly
Tapetum lucidum
- “Reflective carpet”
- Increases light perception under conditions of poor illumination
Does the retinal pigmented epithelium have pigment where the tapetum lucidum is present?
Little to none
Three parts of the retina
- Sensory/optical part = contacts the choroid
- Non-sensory/ ciliary part = outer nonpigmented epithelium of ciliary body (secretes aqueous humor)
- Iridal = posterior pigmented epithelium
The retina is nourished by
vessels of the choroid and by retinal vessels entering via the optic disk
Purpose of sensory/optical retina
sends visual images to the brain
How many layers does the sensory retina have
10
Sensory retina is held in place by
the vitreous body
In the sensory retina, the combined nerve fiber layers converge on optic disc to form
the optic nerve
General concept of optical retina
- Light passes through layers of the retina and stimulates photoreceptor cell (rods and cones)
- Impulse is passed to bipolar neurons, then to ganglion cells
- Axons of ganglion cells form nerve fiber layer. These fibers converge at the optic disk (papilla) and leave the eye as the optic nerve (CN II)
Additional cells with supporting roles include: Amacrine cells, horizontal cells, Muller cells
Path of light and visual perception
- Tear film
- Cornea
- Aqueous humor
- Pupil
- Lens
- Vitreous humor
- First 8 layers of retina
- Stimulating rods or cones
- Absorbed by retinal epithelium
- Visual impulse created then passes in reverse order from rods and cones to bipolar cells, ganglion cells, and to optic nerve of the brain
Outermost layer of the retina
Retinal pigmented epithelium
Retinal pigmented epithelium consists of
Flat polygonal cells resting on a basement membrane
Purpose of retinal pigmented epithelium
Transport of nutrients and metabolites to the rods and cones, light absorption, and phagocytosis
Photoreceptor layer has neurons called
rods and cones
Rods and cones have outer and inner segments connected through
a cilium
Rod structure
- Inner segment of rods is long and thin
- Contain flattened membranous disks containing pigment rhodopsin (vit A)
Purpose of rods
Responsible for vision in dim light
Cone structure
- Inner segment of cones has a broad base
- Disks contain lodopsin
Cones purpose
Responsible for vision in bright light and color vision
Refractive media - vitreous body location
- Occupies space between lens and retina
- 4/5 of eyeball
Refractive media - vitreous body structure
- 99% water and rich in hyaluronic acid
- Gel cortex, liquid center
Function of vitreous body
Aids in maintaining shape, and retinal appostion
Refractive media - lens is surrounded by
a capsule that is thick anterior surface
Anterior epithelium of the lens
- Simple cuboidal cells
- Apical towards lens fibers
- At the equator, elongate and differentiate in to lens fibers
Lens fibers
- Prism shaped cells, lack nuclei, interdigitate extensively and have gap junctions
- Differentiation and growth of lens throughout life
Refractive media - lens suspended by
zonular fibers from the ciliary processes
Refractive media - lens loses vascular supply after
development
The conjunctival epithelium is either
psuedostratified columnar or transitional epithelium that becomes stratified squamous near the eyelid margin
Third eyelid purpose
- Protects eye, removes foreign bodies
- Gland of 3rd eyelid contributes to 30-50% of aqueous portion of the tear film via multiple very small ductules
Third eyelid corresponds to
a fold of the conjunctiva formed by hyaline cartilage in ruminants and dogs and elastic cartilage in horses, pigs, and cats
What is the third eyelid lined by
conjunctiva
What may give the surface of the 3rd eyelid a cobblestone appearance?
Aggregated lymphatic nodules located under the conjunctiva surface
Purpose of the lacrimal gland
Tear film moisturizes, lubricates, and protects
Lacrimal gland structure
- Tubuloalveolar seromucinous acini composed of secretory cells filled with small granules
- Myoepithelial cells are present at base
Three layers of tear film
- Oily portion produced by meibomian (tarsal) glands. The oily portion is the superficial layer of a tear film
- Aqueous portion consisting of sero-mucous material produced by lacrimal glands, and the glands of the third eyelid
- Mucous portion produced by goblet cells in the conjunctiva
