9/13 Eye Conditions - Woodbury Flashcards
eye formation: retina and lens
- optic vesicle induces overlying ectoderm to differentiate → lens epithelium
- optic vesicle folds on itself and pulls forming lens from the surface ectoderm
- lens placode becomes detached from ectoderm
- outer retinal layer differentiates → Retinal Pigmented Epithelium & Neural Retina (inner layer)
- 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
optic sheath and relation to meninges
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
terms:
- canthus (lat vs med)
- caruncle
- iris
- cornea
- sclera
- limbus - importance?
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
muscles/nerves involved with opening and closing eye
corneal reflex review
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!
lacrimation
innervations that make it possible
dry eye lacrimation pathway
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
eye structure
three concentric spheres
- complete tough outer layer : sclera & cornea
- 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
- inner layer : retina
* incomplete anteriorly
fluid-filled segments of eye
- posterior segment: retina to back of lens
- filled with gelatinous vitreous humor
- stable; slow turnover
- 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
functions of anterior eye
1. regulate light intensity
- iris has 2 opposing muscle groups that regulate pupil diameter
- sphincter pupillae [parasymp CN III]
- loss of PSNS fx → blown pupil (mydriasis
- 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!
normal vision vs nearsighted vs farsighted
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
lens anatomy
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)
accomodation reflex
why your eyes get tired after prolonged reading
- convergent eye movement
- pupillary constriction
- 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)
lens and aging
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
functions of ciliary body
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!
functions of posterior eye
- converting light image into neural signal
retina maturation
- development of original retinal layers
- relationship to retinal detachment
early retina has 2 discrete layers
- outer layer → Retinal Pigmented Epithelium
* NOT a neural layer - 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)