Eyes- Myrna Flashcards
give 6 functions of the eyelid
- protection
- exclude light
- sweep foreign body from anterior surface
- spread tear film
- lubricate edges of lids
- pump ocular tear film
what are the 5 muscles of the eyelid and what part of ANS innervates each?
- orbicularis oculi- parasympathetic, motor of CN VII; only muscle that contributes significantly to closure of lids
- retractor anguli oculi: parasympathetic; pulls eyelids from sides so eye not perfect circle
- levator anguli oculi: parasympathetic
- levator palpebrae superioris: parasympathetic, CIII; main muscle that elevates the upper lid
- muller’s muscle: sympathetic of CN V; sympathetic; keeps lids tonically retracted
what nerves are sensory to the eyelid?
branches of V (trigeminal)
maxillary division:
zygomaticotemporal nerve: lateral dorsal lid
zygomaticofacial: lateral ventral lid
ophthalmic division:
frontal (supraorbital) nerve: middle portion of upper lid
infratrochlear nerve: medial dorsal and ventral lid
what are the 4 parts of the nasolacrimal system?
- lacrimal gland
- gland of the 3rd eyelid
- precorneal tear film
-lipid (meibum; prevents evaporation)
-serous: watery
-mucous: from conjunctival goblet cells - drainage system for tears:
-dorsal and ventral puncta, then to dorsal and ventral canaliculi, out through nasolacrimal sac
what is the function of the precorneal tear film? (4)
- maintain optically uniform surface
- remove foreign material and debris
- provide nourishment to cornea (cornea avascular)
- prevent infection
where is aqueous humor located?
anterior and posterior CHAMBERS!;
posterior chamber has anterior and posterior segments!!
posterior segment also called vitreous body/vitreous chamber
what is the function of the fibrous layer of the eye? (4)
- optical element
- protection
- determines shape of globe
- site of insertion of extraocular muscles
describe the relative hydration of the cornea and how this is problematic based on its structure
must be dehydrated to be transparent; but is essentially a sponge in a liquid sandwich, anteriorly covered by tears and posteriorly covered by aqueous humor; so is very easy to get water-logged and hazy and since it is so thin this condition can progress quickly to eye bursting
what are the 4 visible parts of the iris?
- peripheral ciliary zone (thickest outermost part)
- collarette: lighter ring; birth defects originate here
- central pupillary zone
- pupillary border: right around pupil
what is the main function of the ciliary body?
accomodation via movement of zonules to change shape of lens capsule and lens
what organ has the highest protein content in the body?
the lens of the eye!
how is the lens held in place?
by zonules/zonary fibers that attach to the lens capsule
what are the 3 functions of the vitreous body?
- transmit light
- maintain shape of eye
- maintain normal position of retina
what are the 3 functions of the retinal pigmented epithelium? (outermost layer of neuroepithelial tunic)
- location of the blood retinal barrier
- transportation of retinol
- phagocytosis and degradation of photoreceptor disc
what is in the inner and outer layer of the photoreceptor layer of the neuroepithelial tunic?
inner: mitochondria
outer: discs and photopigments
describe the intraocular portion of the optic nerve (3 portions)
- retinal: optic disc, papilla, nerve head; forms a physiologic cup
- choroidal
- scleral: contains lamina cribrosa
describe the orbital part of the optic nerve (3)
- from the lamina cribrosa to the optic foramen
- covered by meningeal sheaths
- considered a nerve fiber tract
describe the intracranial portion of the optic nerve
- from optic canal to optic chiasm
- most fibers cross or decussate
- percentage of crossing depends on the species
describe optic tracts
- continuations of optic nerve as crossed and uncrossed fibers
- synapse in 3 places:
-with lateral geniculate body to make up the optic radiation to the visual cortex
-with rostral colliculus for orientation to visual stimuli; sensitive to horizontal stimulus movement
-with pretectal nucleus as efferent parasympathetic occulomotor nuclei
what is the ocular fundus? what is it composed of? (4)
the internal surface of the posterior aspect of the eye;
1. retina
2. retinal vessels
3. optic disc
4. parts of the choroid and sclera that may be seen through the retina
compare and contrast a transilluminator and a direct ophthalmoscope
transilluminator is a bright diffused light source that is useful for PLRs and basic eval of adnexa (everything but eye and optic nerve) and globe
while a direct ophthalmoscope is a bright focused light source that can localize lesions within globe and is designed to evaluate the fundus
what is tropicamide used for?
short acting mydriatic (dilating) agent for eye exam; parasympathetic
what is proparicaine used for?
topical numbing agent for eye exam and diagnostic if patient too painful to examine; is epitheliotoxic so don’t send home for pain management
describe the schirmer tear test
measures aqueous part of tear film, but must get logistics right
how is fluorescein stain used in eye exam?
detecting corneal ulceration; attaches to hydrophilic stroma of cornea and will stick anywhere there is a gap
describe tonometry/glaucoma test
measure intraocular pressure (glaucoma = elevated IOP, low IOP = uveitis)
can use pen with local anesthetic or tonovet without anesthetic
what are the 5 reflexes/responses of the neuroophthalmic exam? describe
- PLR: stimulus is light, receptor in retina, afferent neuron is CN II, efferent is CN III, effector is iris sphincter muscle, response is pupil constriction
- dazzle: stimulis is bright light; receptor in retina; afferent CN II; efferent CN VII; effector is orbicularis oculi; response is blink or retraction
- menace: stimulus is hand motion, receptor in retina, afferent is CN II, efferent is CN VII; effector is orbicularis oculi, response is blink or retract
- palpebral blink: stimulus is touching eyelids, receptors in skin, afferent in CN V (either ophthalmic or maxillary branches), efferent is CN VII, effector is orbicularis oculi, response is blink
- corneal blink: stimulus is touching cornea, receptors in cornea, afferent is CN V (oph), efferent is CN VII, effector is orbicularis oculi, response is blink
