9/13 Eye Conditions - Woodbury Flashcards

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1
Q

eye formation: retina and lens

A
  1. optic vesicle induces overlying ectoderm to differentiate → lens epithelium
  2. optic vesicle folds on itself and pulls forming lens from the surface ectoderm
  3. lens placode becomes detached from ectoderm
  4. outer retinal layer differentiates → Retinal Pigmented Epithelium & Neural Retina (inner layer)
  5. surrounded mesenchyme becomes tough outer sclera and inner Uvea (vascular choroid and Ciliary body/muscle)

adult eye ends up with 3 distinct layers:

  • tough, fibrous outer layer: sclera/cornea
  • vascular uvea
  • cornea
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2
Q

optic sheath and relation to meninges

A

optic sheath is continuous with meninges as a result of devpt (eyes develop as extensions from same tissue as brain)

implication: optic nerve is surrounded by subarachnoid space in which csf flows

  • high ICP leads to compression of optic nerve → impaired venous return
  • causes head of optic nerve to swell
  • can be visualized as papilledema

fun fact: swelling from other causes = intraocular optic neuritis or papillitis

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3
Q

terms:

  • canthus (lat vs med)
  • caruncle
  • iris
  • cornea
  • sclera
  • limbus - importance?
A

canthus: corners of eyes (lateral vs medial)

caruncle: area near medial canthus

iris: colored portion plus pupil

sclera: white of eye

cornea: clear layer over iris; continuous with sclera

limbus: jx between cornea and sclera

  • imp bc it contains stem cells that can repair cornea if damaged
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4
Q

muscles/nerves involved with opening and closing eye

corneal reflex review

A

CLOSING

obicularis oculi m. [CN VII → motor limb of corneal reflex]

  • orbital portion
  • palpebral portion [eyelid]

OPENING

levator palpebrae [skeletal CN III]

superior tarsal m. [sm muscle - SNS innervation. application: drooping eyelid when tired!]

→ both connect to tarsal plate (conn tissue connection to tip of lid)

corneal reflex:

  • touch conveyed by afferent of CN V → chief sensory nucleus → facial motor nucleus bilaterally → signal to close conveyed on efferent of CN VII → blink!
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5
Q

lacrimation

innervations that make it possible

dry eye lacrimation pathway

A

lacrimal gland is superior and lateral to eye

both SNS and PSNS innervation

  • PSNS: CN VII → greater petrosal → pterygopalatine ganglia
  • application: dry eye signaled via CN V, lacrimation stimulated via component of CN VII (similar pathway to corneal reflex)

lacrimation is swept by blinking toward medial side → drained via lacrimal ducts near caruncle → inf nasal meatus

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6
Q

eye structure

A

three concentric spheres

  1. complete tough outer layer : sclera & cornea
  2. vascular middle layer : uvea
  • ends anteriorly at ciliary body and iris
  • appears to have a hole in it at the pupil BUT actually sealed off by lens posterior to pupil
  1. inner layer : retina
    * incomplete anteriorly
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7
Q

fluid-filled segments of eye

A
  1. posterior segment: retina to back of lens
  • filled with gelatinous vitreous humor
  • stable; slow turnover
  1. anterior segment: lens forward to cornea
  • filled with aqueous humor
  • constantly replenished
  • further subdivided into…
    • posterior chamber (behind iris)
    • anterior chamber (in front of iris)
    • communicate with each other through the pupil
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8
Q

functions of anterior eye

A

1. regulate light intensity

  • iris has 2 opposing muscle groups that regulate pupil diameter
  1. sphincter pupillae [parasymp CN III]
    • loss of PSNS fx → blown pupil (mydriasis
  2. dilator pupillae [symp]
    • loss of SNS fx → miosis
    • dilator can pull on sphincter → spasm in segment of dilator causing misshapen “tadpole” pupil

2. focus light on retina

  • light refracted by cornea and lens → focuses rays on retina
    • cornea = FIXED : does most of bending (dependent on tear film and air/liq interface)
    • lens = VARIABLE : fine tuning
  • RECALL: retina receives images 180deg flipped → issue with upper visual field is issue with lower part of retina!
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9
Q

normal vision vs nearsighted vs farsighted

A

normal: image focused on retina

myopia (near): image focused ant to retina

hypermetropia (far): image focused post to retina

  • all issues with either focusing apparatus or with structure of eye
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10
Q

lens anatomy

A

variable lens

zonules (suspensory ligaments) : pull on lens, flatten it when focusing on distant obj

ciliary muscle (component of ciliary body)

  • when relaxed, internal diameter is large → puts tension on zonules, lens is flattened
  • when contracted, releases tension on zonules → lens is rounded

radial muscle fibers (unknown fx, unknown innervation)

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11
Q

accomodation reflex

why your eyes get tired after prolonged reading

A
  1. convergent eye movement
  2. pupillary constriction
  3. lens accomodation
    * 2&3 primarily PSNS, involve sphincter muscles (iris, ciliary mm; innervation from CN III → ciliary ganglia → ciliary nerves)

accomodation for visualizing things that are close requires muscle tension! → eyes get tired after accomodating for a while (ex. after reading for a long time)

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12
Q

lens and aging

A

accomodation is PASSIVE for the lens, limited only by elasticity

early in life, lens is pliable → shape determined primarily by elastic capsule

as a person ages, lens compliance changes → ability to change shape is compromised

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13
Q

functions of ciliary body

A

1. control lens shape (accomodation)

2. produce aqueous humor (fills ant and post chambers)

  • aqueous humor flows towards uvea-sclera jx, collects in Canal of Schlemm → drains to venous system
  • imbalance? increased IOP! glaucoma!
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14
Q

functions of posterior eye

A
  1. converting light image into neural signal
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15
Q

retina maturation

  • development of original retinal layers
  • relationship to retinal detachment
A

early retina has 2 discrete layers

  1. outer layer → Retinal Pigmented Epithelium
    * NOT a neural layer
  2. inner layer differentiates → 3 distinct neural sublayers, and space between layers disappears
    * all four layers of the retina become intimately associated*

during retinal detachment, space that exists during devpt reappears (i.e. neural layers separate from RPE)

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16
Q

layers of retina

A
  1. retinal pigmented epithelium (RPE)
  2. outer nuclear layer : photoreceptors
  3. inner nuclear layer : interneurons
  4. retinal ganglion cells (RGCs)
    • output cells of retina : only axons that leave retina, eye → form optic nerve

also have a few notable structures between retinal layers

  • outer plexiform layer: synapses between photoreceptors and interneurons (inner/outer nuc layers)
  • inner plexiform layer: synapses between interneurons (inner nuc layer) and RGCs
17
Q

photoreceptors

A

rods : low light conditions

cones : bright light, color vision

  • long/med/short wavelength cones (correspond to R/G/B)

structure

  1. outer segment: filled with photoreceptors (absorbing light, starting signaling cascade)
    • apex is buried in RPE - critical for normal fx.
  2. inner segment: powerplant (mito, ribo → generating proteins for outer segment)
    • comprise outer nuclear layers
  3. synaptic body
    • comprise outer plexiform layer

rods : use stacks of discs studded with photoreceptors (generated at top, migrate/degraded at bottom in RPE)

cones : pl membrane is loaded with photopigments, travels in a sinusoidal path

18
Q

what is the relationship between photoreceptors and RPE?

A

photoreceptors need RPE fx for survival!

why? ex. rods

  1. discs containing photoreceptors are continually generated at Inner:outer segment jx
  2. new discs are pushed towards apex over approx 2 weeks
  3. “spent” discs are phagocytized by RPES

implication: pathologies that compromise RPES compromise photoreceptors → threaten vision!

19
Q

corneal layers

corneal fx

pathology

tx

A
  1. tear film
  2. corneal epithelium (stratified squamous)
  3. Bowman’s membrane
  4. substantia propria (thick)
  5. Descemet’s membrane
  6. corneal endothelium
    • constantly pumps fluid out of cornea to maintain transparency

underneath: aqueous humor

pathology: failure of corneal endothelium → vision issues, clouding of cornea (hydrops)

tx: cadaveric transplant

  • successful bc cornea is avascular, so v little immune surveillance (don’t have to donor match)
20
Q

Alport Syndrome

A

mutation in any of Type IV collagen genes → affects basement membrane formation

  • 2 out of 3 genes on X chromosome, so males preferentially affected

complications: kidney failure is most serious; vision/hearing can be compromised

  • keratoconus
  • anterior lenticonus (v strong corr)
  • hearing bc basement membrane of Organ of Corti also affected
  • kidney issues bc blomerular basement membrane altered → fibrosis/kidney failure
21
Q

Wilson’s Disease

A

aka hepatolenticular degeneration

single gene mutation affects Cu handling

  • Cu accumulates in liver
  • plasma ceruloplasmin drops
  • plasma free Cu increases
  • Cu deposits in body tissues

Cu in liver → fibrosis/cirrhosis

Cu in cornea → Kayser-Fleisher ring

damage to putamen → neuro sx

22
Q

glaucoma

what it affects

types: diffs

A

pathology of anterior/posterior chamber

  • affects optic nerve, but has origins in anterior segment
  • issues with overproduction or poor reabs of fluid will lead to exit at point of least resistance : optic nerve (where RGC axons coalesce and turn 90deg)

two forms: open angle and closed angle (named for location of aq humor reabs - anterior chamber angle, jx of sclera/uvea)

  1. open angle: fluid has unimpeded access to angle, but reabs is reduced
    • slow onset of optic nerve damage
  2. closed angle: angle is blocked
    • often due to ant displacement of lens → ant displacement of iris at angle
    • rapid onset, acute loss of vision
23
Q

glaucoma pathophys

A

pathology within anterior segment affects optic nerve and retina

  • incr IOP compromises axons in optic nerve, leads to cupping
  • untreated, neurons generating axons die & downstream targets of axons in LGN (lat geniculate nucleus) die
24
Q

glaucoma tx

A
  1. pharmacological
  2. mechanical
  • stent in anterior chamber to reinforce connection to Canal of Schlemm
  • IF having cataract removed as well
25
Q

presbyopia

A

lens becomes less pliable with age

  • capsule can squeeze, but lens is not pliable enough to change shape

full accomodation usually compromised by 5th decade

26
Q

cataracts

A

loss of optical function of the lens

  • lens grows naturally throughout life, thickening
  • can eventually grow to a point where it obstructs the vision it’s supposed to facilitate

most common cause : senile cataract

27
Q

macular degeneration

what is the macula?

2 forms & characteristics

A

macula: region of retina encompassing fovea

  • where best vision occurs

macular degeneration begins in retina or underlying choroid

two forms of age-related:

  1. DRY : drusen (debris) accumulation between choroid and RPE → interrupts vascular supply of RPE → interrupts fx of photoreceptor cells
  • most common
  • slow progression
  • no current tx
  1. WET : abnormal angiogenesis → leaking exudate into area between choroid and RPE → formation of scar tissue, interrupting nutrient supply
  • less common
  • rapid progression
  • tx: block new vessel formation
28
Q

Stargardt disease

A

mutation leading to buildup of toxic vitA derivative in outer segment

  • toxin is passed to RPEs when outer segment membranes are phagocytized
  • pathology in photoreceptors → death of RPEs → death of photoreceptors

fovea affected first : pts lose vision in early teens

  • vision loss similar to MD, but sooner
29
Q

Retinitis Pigmentosa

A

mutations in any of multiple geners involved in signal transduction

signal transduction: light → activates receptor → activates transducin → activates PDE → inactivates cGMP → closes channels

initially affects rods → night blindness, loss of peripheral vision

  • “tunnel vision”
30
Q

diabetes and vision

A

vision loss consequent to vascular changes due to diabetes

  • leading cause of blindness in adults 20-74

diabetic retinopathy (neovascularization between retina & vitreous humor)

  1. damaged vessels leak → retinal edema, ischemia
  2. retina releases angiogenic factors → new vessels formed
  3. more leaking → scar formation and adhesions to overlying vitreous
  4. scar contraction pulls on neural retina → separation from underlying RPEs

→→→ photoreceptors are detached from blood supply and will die unless reattached

31
Q

diff between wet macular degen and diabetic retinopathy

A

wet MD : angiogen between choroid and RPEs

diabetic retinopathy : angiogen between retina and vitreous humor

32
Q

blood supply to eye

what happens when you occlude vein or artery???

A

internal carotid → opthalmic artery

  • many orbital and ocular branches
  • CENTRAL RETINAL A/V (down middle of optic nerve)
    • perfuse and drain inner 2/3 of retina

Central Retinal Artery Occlusion (CRAO)

  • pale retina
  • attenuated branches
  • no hemmorhage

Central Retinal Vein Occlusion (CRVO)

  • hemorrhage, edema
  • “squashed tomato sign”
33
Q

retinoblastoma

A

most common malignant cancer of eye in young children

cause: mutations in Rb gene (chr13)

  • Rb is normally tasked with inactivating E2F protein
  • exception: during division, when G1 CDKs P and inactivate it temporarily

mutation leads to permanent inactivation → E2F not sequestered → aberrant proliferation, destroys retina architecture

sx: leukocoria when testing light reflex

  • unilat = spontaneous
  • bilat = familial