4-Eye Flashcards
What holds the eye in place?
The bony orbit
List the tunics of the eye
- Fibrous tunic(outer)
- Vascular tunic(middle)
- Neural tunic(inner)
Fibrous tunic(parts)
- The sclera
- The cornea
Vascular tunic(parts)
- Choroid
- Ciliary body
- Iris
Neural tunic/Retina(parts)
- Retinal pigment epthemlium(outer)
- Neural retina(inner)
- The photosensitive region ends at the ora serrata but both layers continue anteriorly and cover the ciliary body and the retina
Sclera(structure, Function)
- White opaque portion of the eye
- Thick dense CT- mainly Type I collagen with a few elastic fibers and few elongated fibroblasts
- Sensory innervation
- Vascularized
- Function: Protective envelope for the internal eye structures. Attached to extraocular eye muscles to allow movement of the eye
Cornea(structure, function)
- Transparent
- Avascular-nutrients com from aqueous humor(fluid on the interior) and lacrimal fluids(tears)
- Highly innervated
- Important for refraction of light into the eye.
- 5 histologically distinct layers
Layers of the cornea
1) Corneal epithelium
2) Bowman’s membrane(Basement membrane)
3) Stroma
4) Descemet’s membrane(Basement memebrane)
5) Corneal endothelium(Simple squamous layer posterior surface of the cornea)
Corneal epihelium
- Stratified squamous nonkeratinized epithelium(5-7 layers)
- Turnover rate ~7days (corneal injury)
- Highly innervated
Stroma
- 90% of corneal thickness
- Type I collagen few elastic fibers and fibroblasts(similar to sclera with different orgainization
- lamella organization is important for transparency
Conjunctiva
- Mucous membrane covering anterior scleraand inside the eyelids
- Stratified columnar epithelium with goblet cells
- Goblet cells contribute to tear film
- Conjunctivitis is inflammation from bacteria virus or allergens
Choroid
- Posterior portion of the vascular tunic
- Loose CT
- Highly vascularized & pigmented
- Provides nutrients to retinal pigment epithelium nad outer layer of neural retina
- Melanocytes give its pigment absorb light that has passed through the retina to prevent visual interference
Ciliary bodies
-A wedge shaped region of the vascular tunica
-Loose CT blood vessels and smooth muscle
-Double laer of cuboidal cells one pigmented and nonpigmented(surface layer)
-Produces aqueous humor
changes shape of the lens
-have ciliary processes
Ciliary processes
- abundant fenestrated capillaries
- Plasma filtrate is trans ported across as aqueous humor
Aqueous humor(flow)
Posterior chamber–>Pupillary aperature–>anterior chamber–>leaves via canal of Schlemm to venous system
Replaced 15x/day
Glaucoma
- Increased ocular pressure due to failed resorption of aqueous humor as sclera can’t stretch
- causes compromised retinal blood flow and progressive retinal damage
- can cause bindness
Ciliary body(lens connection)
-Zonule fibers that connect to the lens capsule forming the suspensory ligament of the lens
Ciliary muscle contraction(function)
-Contraction of ciliary muscles reduces zonule fiber tension and causes the lens to bulge/become more convex for focusing n NEAR objects- called accommodation
Ciliary muscle relaxation(function)
-relaxation of ciliary muscles increases tension on the zonule fibers cause the lens to flattento focus on far objects
Iris
- Posterior surface has a lot pigment cells that block the light from passing through
- pigmented cells on the anterior surface and within stroma of the iris give eye color (dark eyes have a lo of pigment cells while blue eyes have less)
- the stroma has smooth muscle
Muscles of the iris
- dilator pupillae muscle(radially oriented)
- sphincter pupillae muscle(circumferentially oriented)
- Control the pupillary aperature
Lens(general parts)
- Biconvex transparent disc that functions to focus light on the retina
- Lens capsule(basement memebrane covers the whole lens
- Subcapsular epithelium
- Lens fibers
- Opaque lens is called cataracts
Subcapsulary epithelium
Single layer of cuboidal cells only on the anterior surface of the lens
At the equator they give rise to the lens fibers
Lens fibers
Bulk of the lens has 2k-3k elongated cells course between anterior and posterior poles of the lens
- generated at the equator and grow very slowly through out life
- As they mature they lose the nuclei and organeles and become filled with proteins called crytallins
Vitreous body
- transparent refractile gel that fills the vitreous cavity located behind the lens
- 99% water also has collagen and hyaluronic acid
- small cells called hyalocytes that produce collagen and hyaluronic acid
- Phagocytotic calls are in low numbers
Retinal pigment epithelium
- Cuboidal to columnar cells with a basal nucleus
-Apically it has melanin granules microvilli and sleeve like extensions that surround tips of photoreceptor cells
Reduce light scatter and phagocytose membrane shedding from from photoreceptors
-Desmosomes, zonulae occludens and zonulae adherens are present to form blood retina barrier
Layers of retina(10) in to out
- Inner limiting memebrane
- Ganglion cell axons(form optic nerve)
- Cell body of ganglion cells
- Inner plexiform layer(synaptic zone)
- inner nuclear layer(cell bodies of bipolar, horiontal and amacrine cells)
- outer plexiform layer (synaptic layer
- Outer nuclear layer(cell bodies of rod and cones)
- Photoreceptor region(rods and cones)
- Retinal pigment epithelium
Photoreceptors
- Rods and cones
- absorb photons cause receptor potential processed in the retinal layers before the retinal ganglion
Rods
- extremely light sensitive, used for low level light(night)
- monochromatic- black and white due to one type of one type of photopigment
Cones
Sensitive to daytime light
-trichromatic blue,red green due to 3 opsins
Colorblindness
red-green colorblindness 2% of males
- both colors on the x chromosomes
Fovea
Region of the retina for high acuity vision
- Rich in cones
- Missing some retinal layers to get the most light in.
The optic disk
- Exit point of the unmyelinated retinal ganglion axons
- Pierce the sclera and acuire myelin sheath and form optic nerve
- no photoreceptors cause a blind spot
