Pediatric Eye Exam, EOM Anatomy, Visual Motor and Sensory Physiology, and Amblyopia Flashcards
Preferred method of teting visual acuity in amblyopic patient
crowded optotypes
what age is fixation obtained
4 months
dilating and cycloplegic drops of choice for kids? how long will they last?
1% cyclopentolate (0.5% cyclopentolate for infants), and phenylephrine. cyclopentolate lasts 6-24 hrs
what is consecutive strabismus
a strabismus that is in the opposite direction of a previous strabismus (for example, exo after surgery for eso)
distances of rectus insertions from limbus? where do the rectus muscles penetrate Tenon’s?
MR 5.5 IR 6.5 LR 6.9 SR 7.7 Insert 10 mm posterior to their insertions
origins of each EOM
- all rectus muscles originate a the annulus of Zinn
- SO originates above the annulus of Zinn, but functional origin is trochlea
- IO originates on periosteum of inferonasal maxillary bone, adjacent to anterior lacrimal crest
- Levator orginates above annulus of Zinn
directions of pull for each EOM w/ respect to visual axis
- MR and LR 90 degrees
- SR and IR 23 degrees
- IO and SO 51 degrees
EOM with longest tendon? shortest tendon? longest arc of contact?
longest tendon: SO (26 mm)
shortest tendon: IO (1 mm)
longest arc of contact: IO (15 mm)
positions of obliques with respect to vertical rectus muscles
obliques are inferior to corresponding rectus muscles
blood supply to EOMs
- lateral muscular branch of the ophthalmic artery supplies LR, SR, SO, LPS. LR receives additional supply from lacrimal artery
- medial muscular branch of ophthalmic artery supplies MR, IR, IO
- the muscular branches then also give off anterior ciliary arteries that supply the anterior segment
location of vortex veins
at nasal and temporal borders of inferior and superior rectus muscles; one is always in the inferotemporal quadrant just posterior to the IO tendon, and another is always in the superotemporal quadrant just posterior to the SO tendon
venous drainage of the EOMs
parallels arterial supply; drain into superior and inferior orbital veins
location of adipose tissue in orbit?
extraconal: stops 10 mm from limbus
intraconal: separated from sclera by Tenon’s (Tenon’s prevents fat from scarring to globe)
only EOM not to originate at orbital apex
inferior oblique
what does Tenon’s fuse with anteriorly and posteriorly
anterior: intermuscular septum
posterior: optic nerve sheath
what to the inferior oblique and inferior rectus pulleys combine to form, and what is attached to this conjoined structure
combine to form Lockwood ligament; neurofibrovascular bundle containing the inferior oblique motor nerve is attached
how long are the recuts muscles?
40 mm each
where do their motor nerves penetrate the SR and SO?
one third of the way from origin to insertion (about 26 mm posterior to insertion)
what nerve is not affected by a properly performed retrobulbar anesthetic?
trochlear nerve (lies outside muscle cone)
injury to the inferior oblique motor nerve may also affect what other structure?
parasympathetic fibers to pupillary constrictor and ciliary muscle run alongside this nerve, so mydriasis and loss of accommodation can occur with injury
which is the only rectus muscle without an oblique muscle running tangential to it?
MR
effect of IR and SR resection and recession on palpebral fissure?
- IR resection narrows PF by lower lid elevation
- IR recession widens PF by lower lid retraction
- SR resection can narrow PF by lower upper lid
- SR recession generally has no effect on PF
most common cause of unilateral visual impairment in American adults younger than 60
amblyopia
T or F regarding amblyopia:
- peripheral vision is relatively spared
- amblyopia from refractive error occurs earlier and is more progressive than other causes
- receptive fields of vision in amblyopic eye are abnormally small
- amblyopic patients have better visual acuity when measured with crowded optotypes compared to uncrowded optotypes
- true
- false; amblyopia from media opacity presents first and progresses more quickly
- false; receptive fields are larger
- false; because receptive fields are larger, there is more difficulty with crowded optotypes
what is grating acuity, and what type of amblyopia is this affected abnormally compared to the other types?
the ability to detect patterns of uniformly spaced stripes; this is tested in Teller Acuity Cards and LEA Grating Acuity Test. Grating acuity is affected LESS than normal optotypes in strabismic amblyopia compared to the other types of amblyopia
what is the neutral density filter effect as applies to amblyopia?
slower decrease in visual acuity when a neutral density filter is placed before the strabismic amblyopic eye compared to eyes with organic disease
a patient with amblyopia has a decentered corneal light reflex in the amblyopic eye when the good eye is covered. what doe this indicated, and what is the approximate visual acuity in this eye?
this indicates eccentric fixation, where light is focused onto a nonfoveal region of there retina; this implies 20/200 or worse and portends worse prognosis for visual recovery
levels of anisometropia that can lead to amblyopia
1.50 D anisohyperopia, 2.00 D anisoastigmatism, 3.00 D anisomyopia
what is isoametropic amblyopia? what levels of refractive error can lead to this type of amblyopia?
large, uncorrected, approximately equal refractive error in both eyes. 2-3 D cycl, 4-5 D hyperopia, 5-6 D myopia
what is reverse amblyopia?
amblyopia to the fellow eye that occurs after patching
when should visually significant congenital cataracts be removed?
by 4-6 weeks after birth, to prevent amblyopia
part time occlusion guidelines for amblyopia
2-6 hours / day
6 hours / day for severe (20/100-20/400)
follow-up interval after visit when patching was initiated
2-3 months
desired endpoint of therapy for unilateral amblyopia?
free alternation of fixation or visual acuity no more than 1 line difference between two eyes
can patching be effective past first decade of life?
yes, especially if no patching had been tried previously
is pharmacologic penalization useful in amblyopia treatment? which patient subset would benefit less from this method?
yes; atropine as effective as part time patching for mild to moderate amblyopia (20/100 or better); can be administered daily, but weekend administration is as effective for mild cases. less effective for myopes, because they don’t rely on accommodation for clear distance vision
side effects of full time patching
reverse amblyopia and strabismus
if no visual improvement is obtained despite occlusive therapy with good adherence, after how long is treatment generally discontinued
3-6 months, but varies
percentage of patient whose amblyopia regresses after treatment cessation?
33%
what is Sherrington’s law? what is an example of a violation of this law?
innervation to agonist causes recirprocal decrease in innervation to antoginst; Duane’s syndrome violates this as MR and LR fire simulataneously
Primary, secondary, and tertiary actions of each EOM
MR: 1 adduction; no additional actions
LR: 1 abduction; no additional actions
IR: 1 depression, 2 excyclotorsion, 3 adduction
SR: 1 elevation, 2 incyclotorsion, 3 adduction
IO: 1 excyclotorsion, 2 elevation, 3 abduction
SO: 1 incyclotorsion, 2 depression, 3 abduction
what gaze positions purely isolate the primary and secondary action of the SR, IR, SO, IO
- at 23 degrees of abduction, SR is pure elevator and IR is pure depressor; conversely, 90 degrees away at 67 degrees adduction these muscles are purely cyclotorsional
- at 39 degrees of abduction, the oblique muscles are pure torsional muscles, and at 51 degrees of adduction they are pure elevators/depressors
what is Hering’s law, and what is an example of a violation of this law?
law of equal innervation, where yoke muscles in two eyes receive equal innervation (example: left MR and right LR have equal innervation on right gaze). DVD violates this
primary v secondary deviation in paralytic or restrictive strabismus
primary is when better eye is fixating, secondary is when worse eye is fixating. because of Hering’s law, secondary deviation is always larger
5 types of convergence
accommodative, fusional, tonic, proximal/instrumental, voluntary
magnocellular v parvocellular v koniocellular
magnocellular in periphery and detect motion but relatively insensate to color; parvocellular in fovea and detect high resolution; koniocellular involved in color vision, esp blue-yellow
gestational time and amount of maximum number of retinal ganglion cells? final number of ganglion cells?
2.2-2.5 million by week 18, then decrease to 1.0-1.5 million by early postnatal life
approximate visual acuity of newborn
20/400
the more dissociating the test, the ____ likely the test will produce normal retinal correspondence
more
name the tests for anomalous retinal correspondence in order of most to least dissociating
afterimage test, Worth 4-dot, red-glass test, amblyoscope, Bagolini striated glasses
what is paradoxical diplopia?
temporary diplopia in a post-strab patient with ARC; refoveation occurs and the diplopia typically is temporary
what is monofixation syndrome
peripheral fusion with the absence of bifoveal fusion due to a suppressive central scotoma
