Vision Flashcards
2 essential functions of the eye
1) focus light on the retina (accomplished by concerted efforts of the cornea + lens)
2) transduction of light energy into action potentials (accomplished by the retina)
anterior chamber of the eye
space between cornea and iris
posterior chamber of the eye
space between the zonule fibers (lens) and the back of the iris
vitreal cavity of the eye
large space behind the lens, occupies by the vitreous body
sclera of the eye
fibrous cover of eye (white of the eye)
cornea of the eye
window into eye; clear covering; main refractive elements
iris of the eye
forms pupil
aqueous humor of the eye
*blood-derived, acellular fluid
*pressurizes the eye + maintains eye shape
*produced by CILIARY BODY
*flows from posterior chamber to anterior chamber
zonule fibers of the eye
ligaments that suspend the lens
ciliary body of the eye
consists of ciliary processes and ciliary muscle
ciliary muscles of the eye
control the shape of the lens
choroid of the eye
blood supply plexus serving outer retina, ciliary body, and iris
fovea of the eye
*area near central retina with a high concentration of photoreceptors (CONES ONLY)
*foveal pit: unobstructed light path
optic nerve of the eye
axons of retinal ganglion cells exiting the retina
blood supply of the eye
*provided by 2 branches of the ophthalmic artery:
1. central retinal artery
2. long and short posterior ciliary arteries
central retinal artery
*supplies blood to the inner retina
*enters via the optic nerve
*branch of ophthalmic artery
long and short posterior ciliary arteries
*form the choroid plexus between the sclera and the retinal pigment epithelium
*supplies blood to the outer retina, ciliary body, and iris
*branch of ophthalmic artery
how does the lens get nutrients
aqueous humor
how does the cornea get nutrients
relies on the tear film for oxygen, nutrients, and disposal of metabolic wastes
why are the lens and cornea not innervated by blood supply
maximizes image clarity
emmetropia
normal vision, in which light is focused at the level of the retina
hypermetropia / hyperopia
*far-sightedness
*when light is focused BEHIND the retina (light goes too far) due to abnormal eye shape (too short) or not enough refractive power
myopia
*nearsightedness
*when light is focused IN FRONT OF retina (light is too near), due to abnormal eye shape (too long) or too much refractive power by cornea and lens
correction for myopia
concave lens
2 functions of cornea
1) refraction
2) protection
refractive function of the cornea
*curvature of cornea accounts for majority of refractive power
*layers are optimized for transparency
*avascular to prevent blood vessels from obstructing the primary light path
protective function of the cornea
*tight junctions in the epithelial layer form a barrier that is impermeable to chemicals and other potentially damaging agents
*highly innervated (mostly nociceptive) by CN V1
function of the lens
*refraction for accommodation:
-fine focus mechanism
-refractive power depends on shape (spherical = higher power = near objects; flattened = lower power = far objects)
what happens in the eye when the lens is not accommodated
*ciliary muscles are RELAXED
*zonule fibers are taught
*lens is FLATTENED
presbyopia
loss of ability to accommodate as we age
accommodation innervation
1) Edinger-Westphal nucleus (preganglionic parasympathetics)
2) ciliary ganglion -> short ciliary nerves
3) ciliary muscle and pupillary constrictor
what produces the aqueous humor
ciliary body
what is path of flow of aqueous humor
*flows from point of origin in posterior chamber -> anterior chamber
*exits the eye to join the venous circulation of the sclera by way of the trabecular network and the Canal of Schlemm
glaucoma
*usually occurs when the aqueous humor cannot drain, causing increased intraocular pressure and putting pressure on the optic nerve head, leading to degeneration of the nerve
*impairment of PERIPHERAL vision
9 layers of the retina
- retinal pigment epithelium
- photoreceptor outer segment
- photoreceptor inner segment
- outer nuclear
- outer plexiform
- inner nuclear
- inner plexiform
- ganglion cell
- nerve fiber
retinal pigment epithelium (layer of the retina)
*forms the blood-retinal barrier
*provides metabolic support of outer retina
photoreceptor outer segment (layer of the retina)
*contains light-sensitive elements (rods and cones)
photoreceptor inner segment (layer of the retina)
synthetic machinery of the photoreceptors
outer nuclear (layer of the retina)
photoreceptor cell bodies
outer plexiform (layer of the retina)
a layer of synapses between photoreceptors and intraretinal relay neurons
inner nuclear (layer of the retina)
cell bodies of relay neurons
inner plexiform (layer of the retina)
synapses of relay neurons to ganglion cells
ganglion cell (layer of the retina)
cell bodies of the ganglion cells
nerve fiber (layer of the retina)
axons of the ganglion cells, which come together at the optic nerve head to exit the eye as the optic nerve (CN II)
cones
photoreceptors specialized for vision in bright light (specialized for COLOR)
rods
photoreceptors specialized for dim-light vision
macular degeneration
affects the fovea (impairment of CENTRAL vision)
ascending visual pathway (from retina to primary visual cortex)
1) axons of the retinal ganglion cells exit the retina and form the optic nerve
2) optic nerve partially decussates in the optic chiasm to form the optic tract
3) axons synapse in the LGN of the thalamus
4) from LGN, axons project to the primary visual cortex (above and below the calcarine fissure)
visual cortex on the right side of the brain represents what visual space?
LEFT half of visual space
axons in the nasal retina…
*receive light from IPSILATERAL visual space
*cross in optic chiasm
*reach the CONTRALATERAL LGN
axons in the temporal retina
*receive light from CONTRALATERAL space
*do NOT cross
*project to the LGN on the same side
retinotopic map of visual cortex
*superior visual space (inferior retina) is mapped below the calcarine fissure
*inferior visual space (superior retina) is mapped above the calcarine fissure
*central visual space is represented most posteriorly
*peripheral visual space is represented more anteriorly
*central vision is represented in a disproportionately large amount of cortical tissue
monocular visual loss
lesion of an optic nerve causes no sight from that eye
bitemporal hemianopia
*lesion of the optic chiasm
*affects the nasal retina of both eyes, causing loss of both temporal visual fields
*a pituitary tumor could cause this
macular sparing
vision is spared in the parafoveal region due to the amount of neural tissue devoted to central visual space (because lesions are rarely extensive enough to obliterate the magnified cortical representation of central vision)
contralateral homonymous hemianopia
*one half of visual space (example, left temporal and right nasal) vision is lost
*can be caused by lesion of optic tract, optic radiation (fibers from LGN to visual cortex), or primary visual cortex (upper and lower)
what happens in the eye when the lens is accommodated
*ciliary muscles are CONTRACTED, causing the muscle to bulge out
*zonule fibers slack
*lens is SPHERICAL
correction for hypermetropia / hyperopia
convex lens
