optho anatomy Flashcards
what are the 3 layers of the eye?
1) innermost retinal layer: nueral retina + retinal pigment epithelium
2) choroid layer: middle vascular layer, contains choroid, iris, ciliary body
3) corneoscleral layer: outer fibrous layer contains sclera and cornea
What are the 3 chambers of the eye?
1) anterior chamber: cornea, iris, lens; aqueous humor
2) posterior chamber: iris, lens, zonule fibers, ciliary body; aqueous humor
3) vitreous humor: lens, zonule fibers, retina; gelatinous vitreous humor
the retina develops from what structure?
primitive diencephalon–>optic vesicle–>optic cup
- inner layer optic cup: neural retina
- outer layer of optic cup: retinal pigment epithelium
what primitive layer does the cornea develop from?
ectoderm
retinal pigment epithelium
nutritional support for photoreceptors; absorbs stray light; phagocytoses shed membrane material from outer segments of photoreceptors
photoreceptors
carry out phototransduction to convert light into neural activity
interneurons of retina
process signals from photoreceptors
ganglion cells of retina
transmit signals from interneurons to the brain via the optic nerve
fovea/macula
contains all cones, no blood vessels and cell spreading to form a pit
-maximize high acuity color vision
optic disk/optic papilla
origination of optic nerve; no photoreceptors=functional blind spot
ora serrata
multilayered neural retina simplifies into single layer columnar epithelium that is not photoreceptive
choroid
highly vascularized, pigmented loss CT layer
ciliary body
regulates fine focus by adjusting shape of lens
contains ciliary muscle (smooth muscle) with parasympathetic innervation
zonule fibers connect ciliary body to lens
what is the source of aqueous humor?
ciliary processes
Iris
adjusts the amount of light entering the eye by changing the size of the pupils
- contains 2 sets of muscles:
1) dilator pupillae (myoepithelial cells): sympathetic innervation; dilate pupil
2) constrictor pupillae (smooth muscle): parasympathetic innervation, constrict pupil
sclera
covers posterior 5/6 of eye
dense opaque connective tissue
point of insertion of extraocular muscles
cornea
- covers anterior 1/6 of eye
- transparent, avascular
- major refractive element of the eye w/ 5 layers
limbus
point of transition from sclera to cornea
- location of canal of schlemm which drains aqueous humor
- if drainage is blocked–>glaucoma
opacification of lens
cataracts
conjunctiva
lines inner surface of eyelid
-composed of stratified columnar epithelium with goblet cells
lacrimal gland
- tubuloalveolar serous gland that secretes tears; large lumens and few ducts
- looks like pancreas w/o islets
myopia
- light rays from distant objects are focused in front of the retina
- causes: eyeball is too long, refraction is too strong
- presents as blurred distance vision, near vision is usually good
- tx: concave lens, refractive surgery
hyperopia
- Light rays from distant objects are focused behind retina
- Overcome in early life by great ability for accommodation
- Vision problems start occurring as accommodation weakens
Causes:
• Eyeball is too short
• Refraction is too weak
clinical:
• Presents later in life
• Youth: no symptoms (accommodation)
• Adulthood: blurred near +/- distance vision
tx:
• Convex lens (+)
• Refractive surgery
astigmatism
-light rays are not refracted uniformly–>multiple points of focus
Causes: non-spherical cornea (egg shaped), non-spherical lens
-clinical: blurry vision
-tx: cylindrical lens, refractive surgery
presbyopia
part of normal aging process
- decreased accomodative ability–>cant bring near objects into focus
- patients hold reading material far away
- tx: convex lens
aphakia
Absence of the lens, which results in the eye being short 20 diopters of refracting power
-can be corrected by things that offer convex power: thick glasses, contact lens, lens implant
esotropia
eye turned in
exotropia
eye turned out
hypertropia
one eye higher than the other
hypotropia
one eye lower than the other
strabismus
misalignment of the visual axes of the eyes due to the eyes not working together
comitant strabismus
- deviation is consistent regardless of gaze
- NO known neuromuscular etiology
- Common in children
incomitant strabismus
- Deviation size increases when the gaze is in the direction of the involved muscle
- Causes include CN palsy, thyroid eye disease, MG and mechanical obstruction
- Less common than comitant strabismus
congential esotropia
- comitant strabismus
- Seen in infants in the first few months of life
- Amblyopia is common
- Treatment is surgery
accommodative esotropia
- comitant strabismus
- Develops between ages 1-4
- Occurs in children who are very hyperopic (farsighted)
- Intermittent at first, but increases over time
- Amblyopia is common
- Excess accommodation → excess convergence (esotropia)
- Treatment is glasses (reduces excess accommodation)
- Many children can wean off of glasses by teenage years
- Outcome is extremely good
sensory esotropia or exotropia
- comitant strabismus
- Occurs in eye with poor vision
- Treatment is with surgery
- Surgery straightens eye, but does NOT improve vision
- Surgery often needs to be repeated within 15 years
idiopathic exotropia
- comitant strabismus
- Begins intermittently, but increases in frequency and duration
- Usually more severe at distance
- Amblyopia is common
- Treatment is observation +/- eventual strabismus surgery
CN 3 palsy
- incomitant strabismus
- Patient presents with ptosis, eye pointed down and out and dilated pupil
- Levator muscle weakness → ptosis (droopy eyelid)
- CN3-innervated EOM weakness → eye pointed “down and out”
- Pupillary fibers weakness → dilated pupil
- Mechanism may be congenital, trauma or aneurysm
- Very difficult to treat, but some patients do well with surgery
CN4 palsy
- incomitant strabismus
- Patient presents with vertical diplopia and a head-tilt away from bad side
- Involves the superior oblique muscle
- Mechanism may be congenital or trauma
- Treatment for mild vertical diplopia is glasses with a prism
- Treatment for severe vertical diplopia is surgery
definition of amblyopia
impairment of vision without any detectable organic lesion of the eye
causes of amblyopia
- Refractive (49%): one eye has more far-sightedness, more near-sightedness or more astigmatism than the other eye (rarely, the cause may be bilateral abnormalities)
- Strabismus (49%): alignment of the eyes such that the image does not fall on one (or both) of the maculas
- Ocular Pathology (2%): cataract, glaucoma or corneal anomaly
What do you correct before you correct strabismus?
amblyopia!
development of amblyopia
o Until the age of 7, poor vision will result if a clear image is not focused onto the fovea of each eye
o This is a CNS problem, and will occur even if the eye is structurally completely normal
o The earlier the onset of amblyopia, the worse the prognosis
when do you patch a child’s eye
before the age of 7!
-patch the strong eye to force the child to use the weaker eye and improve the amblyopia
- Must be a sticky, bandaid-like patch
- Amount of time patient needs to wear patch to improve vision is related to two things:
- Degree of initial visual impairment
- Age at time of first noticing amblyopia (the younger the age, the less patch time needed)
- Once vision is improved, patient must continue to wear patch 1 hour per day until age 8-9
When patches absolutely do not work you can dilate the good eye with atropine
