visual system Flashcards
cornea/sclera
major refractive structure, sclera is the insertion pt for muscles
epithelium: stratified squamous cells, highly regenerative capacity
bowmans membrane: acellular layer of unorganized collagen fibers, barrier to infection can heal but scars can form
stroma: organized type 1 collagen bundles binds water, maintains corneal clarity, corneal thickness
descemets membrane: corneal endothelial cells, increases in thickness w/age
endothelium: simple squamous epithelium, pumps water out of stroma
uvea (choroid)
a highly pigmented vascular tunic between the sclera and retina. Absorbs stray light:
Vessel layer: med sized arteries and veins, loose CT and melanocytes
Choriocapillary layer: fenestrated capillaries arranged in single plane
Bruch membrane: amorphous hyaline that the RPE rest on
Uvea (ciliary body)
expansion of the stroma of choroid near lens
contacts 3 regions: vitreous body, sclera, posterior chamber/lens
has projections called ciliary processes that project toward lens
Trabecular meshwork within ciliary body near limbus (aqueous humor drained from anterior chamber via trabecular meshwork)
Uvea (iris)
covers lens, regulates the amount of light reaching the retina
Anterior aspect made of vascular loose CT with interspersed melanocyes, the number of which determines eye color
posterior surface is a double layer of pigmented epithelium (absorbs light)
2 muscle masses layer on pigmented epithelium and regulate iris opening (pupil diameter)- radially arranged myoepithelial cells form dialator pupillae m (sympathetic innervation)
concentric smooth muscles bundles at the pupil margin and form the sphincter pupillae (Parasym innervation)
Anterior and posterior chamber
anterior chamber: between cornea and iris, contains aqueous humor, avascular, involved in maintaining ocular pressure
post chamber: between iris and lens aqueous humor produced by the ciliary processes in the posterior chamber and passes thru pupil
from ant chamber the aqueous humor drained via trabecular meshwork, and then canal of schlemm that drains into venous system
lens
very transparent (avascular with little ECM)
Capsule- ECM surrounding the lens
Epithelium- ant surface of lens
lens fibers- body of lens (no organelles)
functions- second to cornea in refractive power, its suspended via suspensory ligaments and zonules attached to ciliary body
Accommodation: when something is far: lens gets thinner and pulled by ciliary muscles and relaxed when near and gets thicker
vitreous body
structural components: neerly acellular mostly type 2 collagen and hyaluronic acid
function/specialization: very transparent structure- 99% water and avascular, nutrition
retina regions
the retina has 2 regions from embryology
neural/sensory retina, retinal pigment epithelium
layers from inner to outer
Ganglion cell layer, inner plexiform, inner nuclear, outer plexiform, outer nuclear, Rods and cones, RPE
Neural sensory retina
Fovea- small pit- region for high acuity vision
Anteriorly the number of neural elements in the retina declines, becoming a signle layer of epithelium (unpigmented that covers the ciliary body
the fovea is avascular, a pit excavation of inner retinal neurons, high cone densitym absebce of rods
Layers: from out to in
- Photoreceptors (rods and cones) light passes thru all other retina layers before it reaches photoreceptors
- Outer nuclear layer: nuclei of rods and cones
- outer plexiform layer: synapses of rods and cone axons with next layer of bipolar neurons
- inner nuclear layer: nuclei of bipolar neurons
- inner plexiform: synapses of bipolar axons with ganglion cells
- ganglion cell layer: nuclei of ganglion cells
- nerve fiberl layer: axons of ganglion cells that converge to form optic nerve
- inner limiting lamina: basement membrane of Müller glial cells
light transduction
light travels thru inner retina to reach the photoreceptors at the back of eye, and then heads the opposite direction to go to optic nerve
photoreceptors segments:
inner segments: organelles for protein synthesis and energy production
outer segments: flattened membrane discs with photosensitive visual pigment
Rods- long and slender outer segments, very light sensitive
Cones: conical outer segments with membrane discs, responsible for high acuity and color vision
retinal blood supply
inner retina: central retinal artery (branch of ophthalmic )
outer retina: choroidal blood vessels (choroicocapillaries)
the retina has a dual blood supply, with the choroid giving the largest blood flow
Retinal pigment epithelium
simple cuboidal melanin containing epithelium behind neural retina and bruchs
Major function of RPE: absorbs scattered light, transports nutrients, spatial buffering of ions, reisomerization, outer segment renewel, secretion of growth factors
how to correct myopia and hyperopia
nearsightedness, with concave lens
hyper, farsightedness, with convex lens
lens cataract
opacification of the lens
nuclear: centerally located
cortical: outside of nuclear region
posterior capsular
glaucoma
increased intraocular pressure
