Sensory Systems - Eye Flashcards
describe layers of orbit
- outer fibrous coat = cornea, sclera
- middle vascular (uveal) coat = iris, ciliary body, choroid
- inner retinal coat = retinal pigmented epithelium and neural retina
describe chambers of the eye
3 chambers:
- anterior (b/w cornea and iris)
- posterior (b/w back of iris and lens w/ attached fibers)
- vitreous cavity (b/w lens and retina)
generally describe the cornea
- transparent
- convex
- avascular (no blood or lymph in central portion)
- 5 layers
- can be transplanted w/o rejection
fxn of the convex shape of the cornea
aid in focusing light and images on retina
how do the central and peripheral parts of the cornea get nutrients?
central: diffusion from aqueous humor
peripheral: blood from limbus vessels
name the 5 layers of the cornea
- epithelium
- Bowman’s layer/membrane
- stroma
- Decemet’s membrane
- corneal endothelium
describe epithelium of cornea
- anterior layer
- non-keratinized stratified squamous
- small microvilli
- pain receptors (trigeminal and oculomotors)
- can regenerate
describe Bowman’s layer/membrane of cornea
- layer of type 1 collagen
- cannot regenerate
- part of stroma
describe stroma of cornea
- lattice of type 1 and type 5 collagen
- ECM rich in chondroitin and keratan sulfate
describe Decemet’s membrane of cornea
- thick (5-10 um) basement membrane
- contains type 7 collagen
- produced by corneal endothelium
describe corneal endothelium
- surface faces anterior eye chamber
- impermeable intercellular spaces that prevent fluid leakage into corneal stroma
generally describe the sclera
- dense irregular CT
- opaque
function of sclera
- protection and structural support
- insertion point for extraocular muscles
what is the limbus?
corneoscleral junction
what is adjacent to the limbus?
trabecular meshwork and canal of Schlemm
describe aqueous humor
fluid resembling plasma, but w/ less protein
what produces aqueous humor?
ciliary body epithelium
describe flow of aqueous humor
anterior chamber -> trabecular network -> canal of Schlemm -> aqueous veins -> episcleral veins
what does obstruction of aqueous humor flow lead to?
increased pressure in eye -> glaucoma
describe the choroid and fxn
- highly vascular nutrient supplier to all eye layers
- contains melanin
- 3 layers
3 layers of the choroid
- Bruch’s membrane
- choriocapillaris (fenestrated caps-supply retina, fovea)
- choroidal stroma
what does the ciliary body consist of?
uveal and neuroepithelial portions
describe uveal portion of ciliary body
- outer layer of choroid (supraciliaris) + ciliary muscle attached to suspensory ligament
- layer of fenestrated capillaries
describe neuroepithelial portion of ciliary body
2 layers of ciliary epithelium:
- outer pigmented layer continuous w/ retinal pigmented epithelium
- inner non-pigmented layer
what does the anterior portion of the ciliary body form?
it is folded to form ciliary processes
what does epithelium in the ciliary processes produce?
aqueous humor
what is the iris?
- continuation of the ciliary body
- anterior part of middle coat (uvea)
what controls size of pupil?
smooth muscle in iris
describe smooth muscle in iris
2 layers:
- circular (sphincter - parasympathetic)
- radial (dilator - sympathetic)
describe the lens
- avascular
- transparent
- elastic
- biconvex
what encloses the lens?
capsule - thick basement membrane like material
how does the lens change shape?
changes shape when tension on suspensory ligament fibers (zonular fibers) changes
what is vitreous humor?
- gel-like, transparent
- water + hyaluronic acid
- fills vitreous chamber
function of vitreous humor
keeps lens and retina in place
what is a cataract?
opacity of lens - associated with aging
first two layers of retina
- retinal pigmented epithelium (RPE)
2. layer of rods and cones (photoreceptors)
describe RPE fxns (3)
- absorbs scattered light rays
- phagocytosis of worn out discs shed from rods
- stores and releases vitamin A to photo receptors
what is the clinical significance of the RPE?
closely adhered to choroid - trauma can dislodge the retina at this site (where there is a space b/w RPE and rest of retina)
what are rods: describe cells, contents, fxn?
- tall cylindrical cells
- outer segments = modified cilia
- have discs from plasma membrane w/ rhodopsin pigment (transducer of light energy)
- fxns in low light and peripheral vision
what are cones: describe cells, contents, fxn?
- shorter cone shaped cells
- outer segments = modified cilia
- have discs and pigments sensitive to red, green, and blue light
- fxn in color vision and bright light
where are cones found in relation to rods?
cones are located more centrally than rods
what photoreceptors are found in the fovea?
only cones
describe renewal of photoreceptors
- outer discs of old rods shed into space b/w outer segments and RPE, which phagocytoses them.
- new discs made from below, move upward, and replace old ones.
cone discs shed and replaced more slowly
what are the posterior retina landmarks?
macula lutea and optic disc - viewed through the pupil by a scope
what is the optic disc?
papilla where the optic nerve fibers exit retina
does the optic disc have photoreceptors?
no
fovea: what is it, fxn, describe photoreceptors?
what: a pit in the center of the macula
fxn: important for visual acuity
photoreceptors: only cones, very closely packed - highly represented in optic nerve and visual cortex = macular vision
describe vessels around macula
- no retinal vessels
- abundant choroid vessels on outside
what is detached retina?
neural retina separated from RPE and from choroidal capillaries which feed photoreceptors, especially in fovea
what is age related macular degeneration?
macular area and fovea lose function due to pigment epithelium behind retina degenerating and forming drusen (white spots) -> allowing fluid leakage behind fovea
what type of vision loss does age related macular degeneration cause?
foveal cones die -> central vision loss -> cannot read or see fine detail
what is a leading cause of blindness?
age related macular degeneration
what is a common eye problem in aging?
glaucoma - increased pressure w/i eye
what causes high intraocular pressure in glaucoma?
anterior chamber cannot exchange fluid properly by normal aqueous outflow
what does the increased pressure in glaucoma lead to?
compromises blood vessels of optic nerve and axons of ganglion cells
retinitis pigmentosa: what is it, what is first sign of disease, what develops eventually?
- rods of peripheral retina degenerate in early stages of disease
- first sign of disease = night blindness
- eventually develop tunnel vision
- black pigment in peripheral retina and thinned blood vessels at optic nerve head
what is spared in retinitis pigmentosa?
only fovea
how do you get retinitis pigmentosa?
hereditary
how do you treat retinitis pigmentosa?
no cure
what is diabetic retinopathy?
eye blood vessels become distorted and multiply
how do you treat diabetic retinopathy?
laser treatment to stop blood vessel proliferation and fluid leakage
what is hereditary retinal dystrophy?
inability of RPE to phagocytize worn out discs from rods
