Anatomy/strabismus Flashcards
(27 cards)
Tenon’s
EOMs penetrate Tenon’s to insert to globe
two divisions - anterior - fuses with conj 1 mm from limbus
posterior - separates orbital fat from muscles
intermuscular septum
fascial extensions from muscles between rectus muscles
fuses with conj 3 mm posterior to limbus
check ligaments
facial extensions between tenon’s and muscle capsule
Sclera thickness at limbus, front of muscles, behind muscles, ON
Memorize thickness: Limbus - 0.8 mm Front of muscles 0.6 mm behind muscles 0.3 mm at ON 0.1 mm
Lockwood’s ligament
fusion of muscle sheaths of inferior rectus and IO
connects lower eyelid retractors
Make sure to disinsert Lockwood’s ligament when doing IR or IO surgery to prevent lower lid retraction
Whitnall’s ligament
fascial extension from levator palpebral superioris to SO nasally in area of the trochlea
Muscle lengths
Tendon lengths
Spiral of Tillaux
Muscle origins
Muscle length - all rectus approx 40 mm
IO is shortest muscle with shortest tendon (36mm, 1-2 mm respect)
SO longest muscle/longest tendon (60 mm, 30 mm)
Spiral of Tillaux MR - 5.5, SR 6.5, LR 7.0, IR 7.7
Recuts muscles origin - Annulus of Zinn,
IO origin - lacrimal crest
SO origin - medial/sup to annulus of Zinn
Blood supply for EOM
Nerve supply to EOM
7 anterior ciliary arteries travel through 4 rectus muscles (All have 2 except LR with 1)
branches of CN enter EOM in posterior 1/3 of muscle on inner aspect
EXCEPT
IO - neurovascular bundle enters mid muscle on outer aspect (some fibers go to ciliary ganglion - can get blown pupil with IO surgery)
Superior division of III - levator and SR
inferior division of III - MR, IR, IO
Felderstruktur fibers vs Fibrillenstruktur
FELD: Per Yi: “I felt like having a smooth grape”
for smooth pursuit
innervated in ‘en grappe’ fashion (multiple small nerve fibers)
Unique to EOM
FIBRILLEN: fast saccades
innervated ‘en plaque’ fashion
large myelinated nerve fibers
Sherrington’s law vs Hering’s Law
Share one eye - INCR innervation of a given EOM accompanied by DECR innervation of antagonist
HERING’s: equal and simultaneous innervation of muscles in each eye concerned with desired direction of gaze
Conditions that defy Hering’s law
DVD
Abberent regeneration of CN III
Duane’s syndrome
Normal fusional amplitudes
Remember 3:6:18 for distance and double for near
Vertical: D - 3, N - 6 (Per san antonio, Otherwise normally 2-3 D)
Divergence: D - 6, N -12
Convergence: D - 18, N 36
Two pathways in visual system
Magnocellular vs Parvocellular
Parvo - 90% of LGN (central VF and macula), develops by 8 mo
Responsible for stereoPsis, two-Point discrimination
“What info”
Magnocellular (10% of LGN)
for motion - “Where info”
parafoveal and peripheral retina
Horopter
Panam’s area
area of maximal stereopsis
region of single binocular vision
locus of all visual point imaged on the retina for a given fixation distance
Panam’s - region around the horopter within which images can be fused.
neurophysiology of amblyopia
anisometropic vs strabismic/deprivational
anisometropic: mild vision deprevation
P cell maldevelopment
Gross steropsis intact
Strab/depriv: severe vision deprivation
M cell maldevelopment
poor steropsis
PEDIG results
FT patching same as 6 hrs patching for severe amblyopia
2 hrs patching same as 6 hrs for mod amblyopia
patching vs atropine - same for mod amblyopia
atropine weekends vs atropine QD - same
amblyopia recurs within first 3 months of d/c penalization tx
more reverse amblyopia with atropine
Levodopa may be an adjunct to patching for pts up to 18 yr old
Monofixation syndrome
type, how to test, prognosis
binocular sensory state in pt with small angle strabismus
- central scotoma with good peripheral fusion
have large latent phorias
Test with worth 4-dot test and 4 BO prism test:
Worth 4 dot: at distance, central scotoma in one eye, so will only see 2 or 3 dots
at near, scotoma shrinks and pt should see all 4 dots if ARN (will see 5 dots if NRC)
4 BO prism test: normally - eye will turn out and then refixate in
in monofixation when prism in front of normal eye - eyes will turn out, but not refixate
in front of scotoma eye - no initial turn out.
= good prognosis for long term alignment
ARC:
tests
corresponding areas of retina have dissimilar relationship to respective foveas
Bagolini test and after image test
also amblyoscope and red glass test
types of amblyopia
complications from patching
stabismic (cong ET 40%, accom ET 25%, Int XT <2%)
Refractive
Deprivation
Contact dermatitis
Strabismus
reverse amblyopia
infantile esotropia
ET > 35 PD refraction normal present before 6 mo, crossfixation early \+ FHx Associated with DVD, IO overaction, latent nystagmus,
Accomodative ET
onset after 1.5 yrs
ET 3 D (can stop crossing after +7)
How to measure AC/A method
Heterophoria method
Lens gradient method
Near/Distance deviation difference
Heterophoria = IPD + deviation at Near - deviation at distance/accomodation in D at near
Lens Gradient: Dev at N (w/lens) - Deviation at N (without lens)/Lens power
Deviation at near - deviation at distance (high AC/A if greater than 10 -15 PD)
intermittent exotropia
most common XT
may be progressive
amblyopia uncommon
congenital XT
rare
large angle deviation
most resolve by 6 months
Assoc: DVD, oblique muscler overaction, Cruzons, albinism, fetal alcohol, CP
