Strabismus

Question 1

How long are rectus muscles?

Answer 1

40mm

Question 2

Longest overall muscle + tendon

Answer 2

SO

Question 3

Shortest overall muscle + tendon

Answer 3

IO

Question 4

Origin of IO

Answer 4

behind lacrimal fossa (periosteum of maxillary bone)

Question 5

Which muscles do nor originate from annulus of zinn?

Answer 5

SO, IO, levator

Question 6

2ndary action of vertical recti?

Answer 6

torsion

Question 7

2ndary action of obliques?

Answer 7

elevation or depression

Question 8

Monofixation syndrome

Answer 8

• binocular sensory state in patient with small angle strabismus (<8pd)
• central scotoma and peripheral fusion present
• 4BO prism test: normal eye (no refixation when over normal eye); scotoma eye (no initial eye turn)

Question 9

Bagolini lenses

Answer 9

• determine retinal correspondence
• break in line is proportional to size of suppression scotoma
• right eye lens at 135, left lens at 45
• fixate on distant light
• esotropia with NRC: A
• exotropia with NRC: V

Question 10

Criteria for refractive amblyopia

Answer 10

High ametropia: +5D, -8D, astigmatism 2.5D

Anisometropia: 1D hyperopia, 3D myopia, 1.5D astigmatism

Question 11

Hering’s law

Answer 11

Equal and simultaneous innervation to synergistic muscles

-2ndary deviation larger than primary deviation

Question 12

Sherrington’s law

Answer 12

Innervation to ipsilateral antagonist decreases as innervation to agonist increases

Question 13

Angle kappa

Answer 13

• angle btwn visual axis and anatomic axis (pupillary axis)

- POSITIVE: causes slight temporal rotation of globe (light reflex appears nasal)–> ROB, toxocara

Question 14

Congenital esotropia

Answer 14

• present by 6 months
• increased freq of CP or hydrocephalus
• usually >30PD
• assoc with DVD, IOOA (involved eye elevates with adduction), latent nystagmus
• Sx: BMR recession, MR recession and LR resection of same eye

Question 15

Accommodative esotropia

Answer 15

• onset 6mos to 7years
• assoc with amblyopia (usually from anisometropia)
• refractive: normal AC/A ratio (tropia within 10pd at distance and near)
• nonrefractive: high AC/A ration (tropia greater at near, reduced at near with plus lens (consider miotics to treat, bifocals)

Question 16

AC/A ratio

Answer 16

Normal: btwn 3:1 and 5:1 prism diopters per diopter of accommodation

• high AC/A when near deviation exceeds distance by >10-15PD
• AC/A= IPD + [(N-D)/accom demand at fixation distance]
• accom demand 20cm=5D
• AC/A=(WL-NL)/D

Question 17

Convergence insufficiency

Answer 17

Exophoria greater at near than distance

-exacerbated by fatigue, drugs, uveitis, Adies, trauma, systemic illness

Question 18

Convergence paralysis

Answer 18

• normal adduction and accommodation
• XT and diplopia on attempted near fixation
• Parinaud’s syndrome: due to intracranial lesion
• Tx: base-in prisms or occlusion

Question 19

DVD

Answer 19

• intermittent deviation of NONFIXING eye (upward deviation)
• assoc with early disruption of binocular development
• does NOT obey hering’s law

Question 20

Bielschowsky’s phenomenon

Answer 20

• DVD

- elevated eye will drift downward when light in fixating eye is reduced

Question 21

IOOA

Answer 21

-2/3 of patients with congenital ET
-Bilateral and asymmetric
-when fixing eye abducted, adducting eye is elevated
-when fixing eye adducted, abducted eye is depressed
V PATTERN
-Tx: IO weakening

Question 22

IO palsy

Answer 22

LIO palsy: worse left gaze, worse right head tilt
-poor elevation in adduction
-normal forced duction (distinguishes from Brown’s)
A PATTERN
-Tx: IR recession, SO weakening if assoc with SOOA

Question 23

SOOA

Answer 23

-depression on attempted adduction
A PATTERN
-Tx: weaken SO with tenotomy or silicone spacer

Question 24

SO palsy

Answer 24

With IOOA: weaken ipsilateral IO +/- ipsilateral IR resection or contralateral SR recession
Without IOOA: ipsilateral SR recession or contralateral IR recession
Harada-Ito for torsional component

Question 25

Double elevator palsy (monocular elevation deficiency)

Answer 25

-unilateral defect of upgaze assoc with ipsilateral ptosis -may be supranuclear 2 TYPES -IR restriction: unilateral fibrosis syndrome -Elevator weakness (SR and IO)

Question 26

Brown's syndrome

Answer 26

SO tendon sheath syndrome - inability to elevate in ADDUCTION - V pattern divergence in upgaze - no SOOA - head posture - abrupt downshoot in ADDUCTION - restricted forced ductions - Tx: SO weakening

Question 27

Treatment of A patterns

Answer 27

IO palsy or SOOA - MR displacement superorly - LR inferiorly

Question 28

Treatment of V patterns

Answer 28

IOOA, congenital ET, craniosynostosis | -MR inferiorly, LR superiorly

Question 29

Duane's retraction syndrome

Answer 29

Hypoplasia of 6th nerve nucleus, midbrain pathology, fibrosis of LR Type 1: limitation of ABDUCTION, retraction in adduction, appears esotropic Type 2: limitation of ADDUCTION, appears exotropic Type 3: limitation of ABDUCTION and ADDUCTION **Avoid muscle resections

Question 30

Mobius syndrome

Answer 30

CN 6 and 7 palsies - aplasia of involved brainstem nuclei - can get exposure keratitis from poor lid closure

Question 31

CPEO

Answer 31

- sporadic or maternal inheritance - Associated with Kearns-Sayre, abetalipoproteinemia, refsum's, oculopharyngeal dystrophy, cardiac conduction defects - absent bells phenomenon

Question 32

Kestenbaum procedure

Answer 32

Bilateral resection/recession to dampen nystagmus/head turn (eyes surgically moved toward head turn)