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Flashcards in BCSC Strabismus Deck (327):
1

What does strabismus mean?

From the Greek work strabismos, meaning "to squint or look obliquely," strabismus refers to ocular misalignment of any cause

2

What is orthophoria?

the ideal condition of ocular alignment under binocular conditions

3

What is heterophoria?

an ocular deviation kept latent by the fusional mechanism (latent strabismus)

4

What is orthotropia?

correct direction or position of the eyes (although a less stringent condition than orthophoria)

5

What is heterotropia?

a deviation that is manifest and not kept under control by the fusional mechanism (manifest strabismus)

6

Eso-

Rotation of the eye such that (s.t.) the cornea --> nasally, fovea --> temporally (--> indicates direction of deviation) (convergent strabismus)

7

Exo-

Rotation of the eye s.t. the cornea --> nasally, fovea --> temporally (divergent strabismus)

8

Hyper-

Rotation of eye s.t. cornea --> superiorly, fovea --> inferiorly (a form of vertical strabismus)

9

Hypo-

Rotation of eye s.t. cornea --> inferiorly, fovea --> superiorly (a form of vertical strabismus)

10

Incyclo-

Rotation of eye s.t. superior pole --> nasally, inferior pole --> temporally (intorsional strabismus)

11

Excyclo-

Rotation of eye s.t. superior pole --> temporally, inferior pole --> nasally (extorsional strabismus)

12

-phoria

A latent deviation that is controlled by the fusional mechanism, so that the eyes remain aligned under normal binocular conditions

13

-tropia

A manifest deviation that exceeds the control of the fusional mechanism, so that the eyes are not aligned under binocular conditions

14

Phoria (n.)

A "latent" deviation in which fusional control is ALWAYS present

15

Intermittent tropia (n.)

A deviation in which fusional control is SOMETIMES present

16

Tropia (n.)

A "manifest" deviation in which fusional control is NEVER present

17

Comitant (adj.)

The same (or not varying by more than a few prism diopters) in all directions of gaze and fixation with either eye

18

Incomitant

Varying in size with direction of gaze or with the eye used for fixating (usually due to paralytic or restrictive cause)

19

Alternating fixation

Fixation moving from one eye to the other spontaneously

20

Monocular fixation

Definite preference for fixation with one eye

21

Congenital/Infantile strabismus

Terms used interchangeably for deviation documented before the age of 6 months

22

Acquired strabismus

Term used for deviation with onset after 6 months, after a period of apparently normal visual development

23

Abbreviations: E, X, RH, LH

Esophoria, exophoria, right hyperphoria, left hyperphoria

24

Abbreviations: ET, XT, RHT, LHT

(Constant) esotropia, exotropia, right hypertropia, left hypertropia

25

Abbreviations: E(T), X(T), RH(T), LH(T)

Intermittent esotropia, exotropia, right hypertropia, left hypertropia

26

Abbreviations: RHoT, LHoT

Right hypotropia, left hypotropia

27

Abbreviations: O, EX = 0

Orthophoria (orthotropia)

28

What does the addition of a prime to the abbreviations for a deviation indicate?

That the deviation occurs at near fixation (e.g., E' indicates esophoria at near)

29

Optical axis

The best fit line for the optical centers of three parts of the eye anatomy: 1) cornea, 2) lens, 3) fovea

30

Pupillary axis

The corneal surface normal that passes through the center of the pupil (since the radius of curvature of the cornea is not the same as the distance between the pupil center and cornea, there should theoretically be only one such line)

31

Visual axis

Line connecting fixation point and the foveal center

32

What are the 7 extraocular muscles?

4 rectus muscles, 2 oblique muscles, and the levator palpebrae superioris

33

Which EOMs does the upper division of CN III supply?

Levator, SR

34

Which EOMs does the lower division of CN III supply?

MR, IR, IO

35

What is primary position?

Positioning such that the eyes are directed straight ahead and the head is straight

36

What is the primary action of a muscle?

The predominant effect on the position of the eye (component of force vector with largest magnitude) when contracting with the eye in primary position

37

What do the secondary and tertiary actions of a muscle refer to?

The second and third largest magnitude components of the force vector generated by muscle contraction with the eye in primary position

38

Approximately how many degrees can each globe be rotated in either direction when in primary position?

50 degrees

39

What is the secondary action of the SR muscle (in primary position)?

Intorsion

40

What is the secondary action of the IR muscle (in primary position)?

Extorsion

41

From where do all the rectus muscles arise?

The annulus of Zinn

42

From where does the SO arise?

The obital apex

43

What angle does the vertical plane passing through the two vertical rectus muscles make with the vertical plane including the visual axis?

23 degrees

44

What angle does the SO form with the vertical plane containing the visual axis in primary position?

51 degrees

45

In what directions is the SO redirected at the trochlea?

Inferior, posterior, and lateral

46

Into which quadrant of the globe does the SO tendon insert?

posterosuperior

47

What are the primary and secondary actions of the SO in primary position?

1) intorsion, 2) depression

48

From where does the IO originate?

the periosteum of the maxillary bone, just posterior to the orbital rim and lateral to the orifice of the lacrimal fossa

49

What angle does the IO form with the vertical plane containing the visual axis in primary position?

51 degrees

50

What are the primary and secondary actions of the IO in primary position?

1) extorsion, 2) elevation

51

From where does the levator arise?

The apex of the orbit from the lesser wing of the sphenoid just superior to the annulus of Zinn

52

The fascial sheath of the levator is connected with that of which EOM?

SR

53

What are the distances of the rectus muscle insertions from the limbus in the order MR, IR, LR, SR?

5.5mm, 6.5mm, 6.9mm, 7.7mm

54

Which EOMs are supplied by the lateral muscular branch of the opthalmic artery?

LR, SR, SO, levator

55

Which EOMs are supplied by the medial muscular branch of the ophthalmic artery?

IR, MR, IO

56

Which veins empty the EOMs?

Superior and inferior orbital veins and the vortex veins

57

What histologic type of muscle is EOM?

voluntary striated muscle

58

Is the ratio of nerve fibers to muscle fibers in EOMs greater than in skeletal muscle?

Yes, 10x greater in EOMs

59

What are the two layers of EOMs?

Orbital layer (acting on pulley system) and Global layer (inserting on globe)

60

Are singly innervated fibers in the EOMs slow twitch or fast twitch?

Fast twitch (80% of orbital layer, 90% of global layer)

61

What are the 3 subgroups of singly innervated muscle fibers in the EOMs?

red (most mitochondria and most fatigue resistant), intermediate, white

62

Do each of the rectus muscles have a capsule extending from origin to insertion?

Yes

63

Of what does the muscle cone consist?

EOMs, EOM sheaths, intermuscular membrane

64

What is the Tenon capsule??

The principal orbital fascia, which forms the envelope within which the globe moves.

65

With what does the Tenon capsule fuse posteriorly?

Optic nerve sheath

66

With what does the Tenon capsule fuse anteriorly?

Intermuscular septum, approximately 3mm from limbus

67

Where do the global layers of the 4 rectus muscles penetrate the Tenon capsule?

10mm posterior to their insertions (posterior to the equator)

68

Where do the oblique muscles penetrate the Tenon capsule

anterior to the equator

69

Which EOMs have fibroelastic pulleys consisting of collagen, elastin, and smooth muscle?

The 4 rectus muscles and IO

70

What do pulleys serve to do for the EOMs?

They serve as functional origins for their respective EOMs

71

From which two EOM pulleys does the Lockwood ligament arise?

IO and IR pulleys

72

Are the lower lid retractors coupled to the conjoined IR/IO pulleys?

Yes, which allows coordination of lower eyelid positioning with vertical eye positioning during vertical gaze shift

73

What is the distance from the rectus muscle insertion of the nerves to the rectus muscles?

26mm (the nerves are located 26mm and further posterior to the rectus muscle insertions), which is relevant for performing muscle surgeries.

74

Does recession strengthen or weaken a muscle?

Weaken

75

Does resection strengthen or weaken a muscle?

Strengthen

76

Why should care be taken to avoid peentration of the Tenon capsule 10mm or more posterior to the limbus?

To avoid prolapse of fatty tissue from within the Tenon capsule and formation of a restrictive adhesion to muscle, intermuscular membrane, or conjunctiva. Such an adhesion would limit ocular motility

77

Where is the sclera the thinnest?

Just posterior to the 4 rectus muscle insertions

78

What are the orientations of the x, y, and z axes according to Fick?

x is medial-lateral (passing through the equator), y is anterior-posterior (passing through the pupil), z is rostral-caudal

79

What is Listing's equatorial plane?

the plane of the globe's equator. It contains both the x and z axes of Fick

80

What is primary position?

the position of the eyes when fixating straight ahead

81

What are the secondary positions?

Gaze straight 1) up, 2) down, 3) right, 4) left

82

What are tertiary positions?

The four oblique positions of gaze: up and right, up and left, down and right, down and left

83

What are the cardinal positions?

There are six cardinal positions: up and right, up and left, right, left, down and right, down and left

84

What is the arc of contact?

The length of muscle actually in contact with the globe

85

What is the secondary action of the superior rectus primary position?

Intorsion

86

What is the secondary action of the inferior rectus in primary position?

Extorsion

87

What is the secondary action of the inferior oblique in primary position?

Elevation

88

What is the secondary action of the superior oblique in primary position?

Depression

89

What is the tertiary action of the superior rectus in primary position?

A D duction

90

What is the tertiary action the inferior rectus in primary position?

A D duction

91

What is the tertiary action of the inferior oblique in primary position?

Abduction

92

What is the tertiary action of the superior oblique in primary position?

Abduction

93

What are the two, quite distinct, definitions of the term field of action?

1) to indicate the direction of rotation of the eye from primary position if the muscle were the only one to contract, 2) to refer to the gaze position in which the effect of the muscle is most readily observed

94

Electromyography can be helpful in evaluating which conditions?

Paralysis, recovery from paralysis, abnormalities of innervation in myasthenia gravis, and muscle atrophy

95

What are ductions?

Monocular rotations of an eye

96

What does the term agonist mean with regard to eye movements?

the primary muscle moving the eye in a given direction

97

What does the term synergist mean with regard to eye movements?

the muscle in the same eye as the agonist that acts with the agonist to produce a given movement

98

What does the term antagonist mean with regard to eye movements?

The muscle in the same eye as the agonist that acts in the direction opposite to that of the agonist

99

What is Sherrington's law of reciprocal innervation?

Sherrington's law postulates that increased innervation (meaning neuronal firing, not actual innervation) and contraction of a given EOM are accompanied by a reciprocal decrease in innervation and contraction of its antagonist

100

What are versions?

binocular eye movements with the eyes moving in the SAME direction

101

What are vergences?

vinocular eye movements with the eyes moving in OPPOSITE directions

102

What does the term yoke muscles mean?

Yoke muscles are 2 muscles (one in each eye) that are the primary movers of their respective eyes into a given position of gaze (e.g., RLR and LMR for right gaze)

103

What is Hering's law of motor correspondence?

Hering's law posits that equal and simultaneous innervation (i.e. neuronal signaling) flows to yoke muscles concerned with the desired direction of gaze

104

What is "primary deviation?"

The amount of misalignment that occurs when the normal eye is fixating

105

What is "secondary deviation?"

The amount of misalignment that occurs when the abnormal (e.g. paretic or restricted) eye is fixating

106

Which is generally larger in the setting of a restriction or paresis, the primary or secondary deviation?

The secondary deviation (relates to Hering's law)

107

What is the alignment of the eyes under complete EOM paralysis?

Divergent

108

What is the AC/A ratio?

The ratio of accommodative convergence (amount eyes turn inward) to accommodation (number of diopters of lens accommodation)

109

What is proximal (instrument) convergence?

An induced convergence movement caused by a psychological awareness of near; this is particularly apparent when a person looks through an instrument such as a binocular microscope

110

What is fusional convergence?

A movement to converge and position the eyes s.t. similar retinal images project on corresponding retinal areas. This is accomplished without changing the refractive state of the eyes and is prompted by biTEMPORAL retinal image disparity

111

What is fusional divergence?

An optomotor reflex to diverge and align the eyes s.t. similar retinal images appear on corresponding retinal areas. It is acomplished without changing the refractive state of the eyes and is prompted by biNASAL retinal image disparity

112

What is the maximum speed of saccadic movements?

500 degrees/sec

113

What are corresponding points on the retinas of each eye?

Points such that their simultaneous stimulation results in the subjective sensation that the stimulating target or targets come from the same direction in space

114

What is anomalous retinal correspondence?

Dissimilar spatial relationships between corresponding retinal areas and their respective foveas

115

What is a horopter?

The 3d subspace (or perhaps more specifically, a curved 2d manifold) within which all points are seen singly for a given fixation point

116

What is Panum's area of single binocular vision?

A superspace of the empirical horopter in which single binocular vision can be achieved through fusion of disparate images (outside the horopter) or by corresponding images (within the horopter)

117

What is fusion?

The cortical unification of visual objects into a single percept that is made possible by the simultaneous stimulation of corresponding retinal areas

118

What is sensory fusion?

An artificial classification that refers to fusion aided by innate retinotopic organization of visual cortex

119

What is motor fusion?

An artificial classification that refers to fusion aided by a vergence movement causing similar retinal images to fall and be maintained on corresponding retinal areas even though natural or artificial causes may otherwise induce disparities

120

In what situation does stereopsis occur?

In situations s.t. retinal disparity is too great to permit the simple superimposition or fusion of the 2 visual directions, but is not great enough to elicit diplopia

121

Which feature of binocular vision allows a subjective ordering of visual objects in depth, or 3 dimensions?

Stereopsis

122

What are the 6 monocular layers of the LGN?

4 dorsal parvocellular layers and 2 ventral magnocellular layers

123

Which retinal ganglion cells project to the magnocellular layers of the LGN?

Parasol retinal ganglion cells (P->M)

124

Which retinal ganglion cells project to the parvocellular layers of the LGN?

Midget retinal ganglion cells (M->P)

125

Which retinal ganglion cells are more highly concentrated in the central retina (midget or parasol)?

midget retinal ganglion cells

126

What is the peak number of retinal ganglion cells in the human retina and when is it reached?

2.2-2.5 million, reached at week 18 of gestation. Number drops to final count of 1.5 million by first few months of life

127

When does refinement of synaptic connections in striate cortex level off?

by age 10

128

What is the benefit of invasion of a deprived eye's relinquished striate cortex territory by the axonal arbors from the non-deprived eye?

Unclear, as visual acuity does not improve beyond normal in the non-deprived eye

129

Does astigmatic amblyopia develop in the first year of life?

No, it appears that astigmatic amblyopia does not develop until age 3

130

When does the critical period for development of strabismic amblyopia appear to begin?

4 months of age

131

What is visual confusion?

simultaneous perception of 2 different objects projected onto corresponding retinal areas (does not happen in the fovea)

132

What is central fusional disruption?

an intractable diplopia involving 1) avoidance of bifoveal stimulation, 2) absence of suppression, 3) loss of fusional amplitudes

133

What is suppression?

alteration of visual sensation involving inhibition or prevention of images from one eye from reaching consciousness during binocular visual activity

134

What is amblyopia?

A unilateral or bilateral reduction of best-corrected visual acuity that cannot be attributed directly to the effect of any structural abnormality of the eye or posterior visual pathways.

135

What is the cause of amblyopia?

Abnormal visual experience in early life. Generally, such abnormal visual experiences are due to one or more of: 1) strabismus, 2) anisometropia or high bilateral refractive errors, 3) stimulus deprivation

136

What is the prevalence of amblyopia in North America?

2% to 4%

137

Are the critical periods for the development of amblyopia due to various causes the same?

No, there are different critical periods for each cause of amblyopia

138

What is the crowding phenomenon?

The finding that Snellen letters or equivalent symbols of a given size become more difficult to recognize if they are closely surrounded by similar forms, such as a full line or field of letters

139

Strabismus having which characteristics is most likely to cause significant amblyopia?

1) constant, 2) non-alternating, 3) esodeviation

140

Which is usually reduced more in strabismic amblyopia, grating acuity or Snellen acuity?

grating acuity (e.g. Teller cards)

141

What is eccentric fixation?

The consistent use of a nonfoveal region of the retina for monocular viewing by an amblyopic eye

142

Below what degree of myopic anisometropia is anisometropic amblyopia rarely seen?

below 3D

143

What is ametropic amblyopia?

Bilateral amblyopia, usually mild, resulting from large, approximately equal, uncorrected refractive errors in both eyes of a young child

144

What magnitudes of bilateral refractive error are generally required for development of ametropic amblyopia?

5D in hyperopia, 6D in myopia

145

What is the most common cause of deprivational amblyopia?

congenital or early acquired cataract

146

Beyond what threshold diameter is a cataract in a child under the age of 6 considered amblyogenic?

3mm when centrally located

147

What are the 3 general steps in the treatment of amblyopia?

1) elimination (if necessary) of any obstacle to vision (e.g. cataract), 2) correction of significant refractive error, 3) force use of weaker eye by limiting use of stronger eye

148

When should removal of visually significant congenital lens opacities occur for optimal recovery?

Within the first 4-6 weeks of life

149

The interval for operations on the first and second eyes in a patient with bilateral congenital cataracts should be no longer than what?

1-2 weeks (amblyopia of different mechanism can develop due to disparity)

150

When should a traumatic cataract be removed in a child under the age of 6 years?

Within a "few" weeks of injury

151

Why is refraction performed with cycloplegia in children?

Accommodation can occur in an uncontrolled manner in amblyopic eyes. If the amblyopic eye is hyperopic, accommodation may or may not cause underestimation of the refractive error. On the other hand, if the eye were hyperopic but not amblyopic, accommodation would likely be used to compensate, and the refractive error would be underestimated. Since no "accommodative correction factor" can be applied to amblyopic eyes, elimination of the accommodation variable is needed to accurately assess true refractive error.

152

Can strabismus develop during patching?

Yes (etiology unclear)

153

How many hours per day of patching is usually prescribed for moderate to severe amblyopia?

>= 6 hours/day

154

What is a Bangerter foil?

A neutral density filter (a filter that reduces the intensity of all wavelengths of light equally, giving no changes in color rendition) that can be used for "penalization" of the better eye in amblyopia

155

What are common forms of penalization?

Pharmacologic (atropine 1% or homatropine 5%), fogging (excessive plus-power lenses), diffusing filters, neutral density filters (Bangerter foil)

156

What are techniques that can reduce the likelihood of (or treat) iatrogenic amblyopia?

1) avoid full-time patching (use part-time patching or penalization), 2) alternate occlusion, 3) pause therapy for 1-2 weeks if concern raised

157

What is the CSM method of reporting visual acuity?

C -- corneal light reflex position, S -- steadiness of fixation, M -- maintenance of fixation with 1 and both eyes

158

What is the induced tropia test?

Evaluation of ability of patient to maintain fixation with either eye under binocular conditions with vertical deviation (usually created with a base-vertical prism)

159

What are the 4 basic types of ocular alignment tests?

1) cover tests, 2) corneal light reflex tests, 3) dissimilar image tests, 4) dissimilar target tests

160

What are the 3 types of cover tests?

1) cover-uncover, 2) alternate cover, 3) simultaneous prism and cover

161

What is the most important test for detecting the presence of a manifest strabismus?

monocular cover-uncover test

162

In performing a cover-uncover test on a patient with a phoria, when will the patient's eyes move?

only when uncovering

163

In performing a cover-uncover test on a patient with a tropia, when will the patient's eyes move?

1) both when covering and uncovering OR 2) only when covering (if fixation alternates)

164

Which test is primarily used to identify a phoria?

alternate cover test -- the eyes are not allowed to fixate simultaneously, disrupting fusion and unmasking phorias

165

Measuring with a prism during which test allows assessment of the total deviation due to both phoria and tropia?

Alternate cover test

166

Measuring with a prism during which test allows assessment of the manifest deviation only?

Cover-uncover test

167

When measuring a manifest deviation with a prism, which eye is covered and in front of which eye is a prism placed?

The fixating eye is covered and uncovered while the prism is placed in front of the deviating eye

168

What are the main types of corneal light reflex tests for ocular alignment?

Hirschberg, modified Krimsky, Bruckner, major amblyoscope

169

What is the conversion of 1mm decentration of corneal light reflex to degrees and prism diopters for the Hirschberg test?

1mm = 7 degrees = 15 prism diopters

170

What is angle kappa?

The angle between the visual axis and the pupillary axis of the eye.

171

What is positive angle kappa?

The fovea is usually temporal to the pupillary axis, meaning the corneal light reflex will be slightly nasal to the center of the cornea. This situation is referred to as positive angle kappa, and simulates exodeviation. Negative angle kappa simulates esodeviation.

172

Why is the Maddox rod test not a satisfactory test for quantifying horizontal deviations?

Accommodative convergence cannot be controlled with the Maddox rod test

173

What test category do the Maddox rod, double Maddox rod, and red glass tests fall under?

Dissimilar image tests

174

What test category do the Lancaster red-green projection test, Hess screen test, and major amblyoscope test fall under?

Dissimilar target tests

175

At what distance is near alignment usually tested?

13 inches (33cm)

176

How is the near point of convergence determined?

By placing a fixation object at 40cm and progressively moving toward the patient until 1 eye loses fixation and turns out. The point at which 1 eye loses fixation is the near point of convergence. (The eye maintaining fixation is the dominant eye)

177

What is the normal near point of convergence?

8-10cm

178

What are the 2 methods of measuring AC/A ratio?

1) Gradient method, 2) Heterophoria method

179

What can be used to measure fusional vergences?

Haploscopic device, rotary prism, bar prism

180

What is the 3-Step Test?

An algorithm that can be used to help identify the paretic cyclovertically acting muscle responsible for a hyperdeviation

181

What are the three steps of the 3-Step Test?

1) Identify which eye is higher, 2) Identify whether worse in left or right gaze, 3) Identify whether worse with right or left head tilt

182

What did the Prism Adaptation Study demonstrate?

A smaller undercorrection rate (about 10% less) when surgery was based on multiple rounds of prism adaptation than standard techniques

183

What are the two classes of tests commonly used to assess sensory binocularity?

1) Worth 4-dot testing, 2) Stereoacuity testing

184

What are the two types of stereopsis tests?

1) contour tests, 2) random dot tests

185

What do contour stereopsis tests involve?

Actual horizontal separation of the targets presented to each eye (with polarized or red-green glasses). Monocular depth cues may be present at lower stereoacuity levels.

186

What do random-dot stereopsis tests involve?

embedding of stereo figures in a background of random dots

187

Why is tropicamide not used alone for cycloplegia in children?

It does not provide sufficient cycloplegia at standard doses in children

188

Which cycloplegic agent has the highest incidence of hypersensitivity reactions?

Atropine

189

What percent of ocular deviations in the pediatric populations are esodeviations?

more than 50%

190

Esotropia must be documented by what age in order to classified as congenital (now referred to as infantile)?

by 6 months

191

IO overaction and dissociated vertical deviation occur in what percent of patients with infantile esotropia?

50%

192

What are the 6 major types of esodeviation?

1) Pseudoesotropia, 2) infantile, 3) Nystagmus and esotropia, 4) accommodative, 5) non-accommodative acquired, 6) incomitant

193

Is persistent asymmetry of monocular horizontal smooth pursuit common in patients with infantile esotropia?

yes, it often persists beyond 6 months, with nasal-to-temporal smooth pursuit impaired

194

When is the preferred time to perform surgery to correct infantile esotropia?

Between 4 and 6 months to achieve optimal binocular vision (including stereopsis)

195

What magnitude of deviation after surgery is considered a successful result of surgery to correct infantile esotropia?

Within 8 prism diopters of orthotropia, with development of monofixation syndrome, is considered successful (even though bifoveal fusion would not be achieved)

196

What is accommodative esotropia?

A convergent deviation of the eyes associated with activation of the accommodative reflex.

197

What is the usual age of onset for accommodative esotropia?

between 6 nonths and 7 years

198

What are the 3 factors in the development of refractive accommodative esotropia?

1) uncorrected hyperopia, 2) accommodative convergence, 3) insufficient fusional divergence

199

What is the primary treatment for refractive accommodative esotropia?

Correction of the full amount of hyperopia, as determined under cycloplegia

200

What are the 4 approaches to management of high AC/A esotropia?

1) Bifocals, 2) long-acting cholinesterase inhibitors, 3) surgery, 4) observation

201

Why are bifocals helpful in high AC/A esotropia?

Greater accommodation is required at near, making high AC/A esotropia worse at near. Reduction in the amount of accommodation required at near with +3D bifocals in turn reduces the amount of accommodative convergence that occurs, thereby improving the esotropia.

202

What is a common cause of acute esotropia?

Artificial disruption of binocular vision due to ocular injury

203

What is the characteristic movement seen with spasm of the near synkinetic reflex?

Substitution of a convergence movement for a gaze movement on horizontal versions

204

What are 3 causes of pseudoexotropia?

1) wide interpupillary distance, 2) positive angle kappa, 3) ocular abnormalities such as temporal dragging of macula (as may occur in ROP)

205

What is the most common type of exodeviation?

intermittent exotropia (latent at times, manifest at others)

206

What is the usual age of onset for intermittent exotropia?

Before age 5 years

207

What are common situations in which intermittent exotropia is manifest?

1) end of the day, 2) fatigue, 3) illness, 4) drowsiness

208

What is the progression of intermittent exotropia in most patients?

Toward constant exotropia

209

What is tenacious proximal fusion?

A proximal vergence aftereffect that occurs in some patients with intermittent exotropia. The aftereffect is due to a slow-to-dissipate fusion mechanism that prevents intermittent exotropia from manifesting at near fixation with a brief cover test

210

What are the 3 primary classifications of intermittent exotropia?

1) Basic type (same at near and far), 2) Divergence excess (worse at distance), 3) convergence insufficiency (worse at near)

211

What is a common criterion used for deciding to perform surgery on a patient with intermittent exotropia?

Manifest deviation more than 50% of the time

212

What is the most common surgical procedure for intermittent exotropia?

Bilateral LR recession

213

When must exotropia present in order to be considered infantile?

before 6 months of age

214

What are usual characteristics of convergence insufficiency?

1) asthenopia, 2) blurred near vision, 3) reading problems in the presence of poor near fusional convergence amplitudes, 4) remote near point of convergence

215

What is one disease in which convergence insufficiency is seen more often than age-matched controls?

Parkinson disease

216

What is convergence paralysis?

Normal adduction and accommodation, accompanied by exotropia and diplopia on attempted near fixation only

217

What are possible sites of lesions leading to convergence paralysis?

1) corpora quadrigemina, 2) nucleus of CN III

218

What is an A-pattern deviation?

A horizontal deviation that is more convergent or less divergent in upgaze than in downgaze

219

What is a V-pattern deviation?

A horizontal deviatino that is more convergent or less divergent in downgaze than in upgaze

220

In what percent of horizontal strabismus cases is an A or V pattern found?

15%-25%

221

What magnitude of difference between upgaze and downgaze is required for an A-pattern to be considered clinically significant?

>= 10 prism diopters

222

What magnitude of difference between upgaze and downgaze is required for a V-pattern to be considered clinically significant?

>= 15 prism diopters

223

Is IO overaction associated with A or V patterns?

V patterns

224

Is SO overaction associated with A or V patterns?

A patterns

225

In which eye and which gaze can ipsilateral SO function be assessed (for over- or under- action)?

Look for ability to depress (or limit elevation) in adduction. Therefore, look at 1) L eye in Right-Down gaze and 2) R eye in Left-Down gaze. If L SO is underacting, L eye will be higher than normal in Right-Down gaze. If R SO is underacting, R eye will be higher than normal in Left-Down gaze. If L SO is overacting, L eye will be lower than normal in Right-Up gaze. If R SO is overacting, R eye will be lower than normal in Left-Up gaze.

226

In which eye and which gaze can ipsilateral IO function be assessed (for over- or under- action)?

Look for ability to elevate (or limit depression) in adduction. Therefore, look at 1) L eye in Right-Up gaze and 2) R eye in Left-Up gaze. If L IO is underacting, L eye will be lower than normal in Right-Up gaze. If R IO is underacting, R eye will be lower than normal in Left-Up gaze. If L IO is overacting, L eye will be higher than normal in Right-Down gaze. If R IO is overacting, R eye will be higher than normal in Left-Down gaze.

227

How much correction should be performed on the horizontal rectus muscles for an A or V pattern strabismus with IO overaction?

Same amount as without an A or V pattern

228

When is upward or downward displacement of the horizontal recti performed for A or V pattern strabismus?

If there is no oblique muscle dysfunction

229

In what direction are the horizontal rectus muscle insertions moved (upward or downward) when addressing an A or V pattern strabismus without oblique muscle dysfunction?

LR insertion toward base of pattern, MR insertion apex of pattern. Moving in a particular direction weakens the muscle in that direction (and strengthens it in the opposite direction). LR needs to be weaker at base, while MR needs to be stronger at base in order to bring eyes inward.

230

What are the 2 components of surgical treatment for V-pattern strabismus (esotropia or exotropia)?

1) horizontal rectus muscle procedure in usual amounts, 2) weakening of IOs if overacting OR horizontal rectus insertion vertical displacement if IOs not overacting

231

What are the 2 components of surgical treatment for A-pattern esotropia?

1) horizontal rectus muscle procedure in usual amounts, 2) horizontal rectus insertion vertical displacement (whether or not SOs are overacting)

232

What are the 2 components of surgical treatment for A-pattern exotropia?

1) horizontal rectus muscle procedure in usual amounts, 2) weakening of SOs if large A-pattern OR horizontal rectus insertion vertical displacement if small A-pattern

233

Are most vertical deviations comitant or incomitant?

incomitant

234

What is primary IO overaction?

IO overaction without associated SO or SR paralysis or paresis

235

What is secondary IO overaction?

IO overaction accompanied by paresis or palsy of SO or SR

236

Primary IO overaction develops between what ages?

1 year and 6 years

237

What proportion of patients with infantile strabismus will develop primary IO overaction?

2/3

238

In which cases of isolated primary IO overaction is a weakening procedure on the IO indicated?

All but the mildest cases of isolated primary IO overaction

239

What is the most prominent finding in IO overaction?

Overelevation in adduction

240

What is the most prominent finding in SO overaction?

Overdepression in adduction

241

What are the clinical features of dissociated vertical deviation (DVD)?

Either eye slowly drifts upward and outward with simultaneous extorsion during periods of visual inattention or occlusion

242

Is DVD usually unilateral or bilateral?

Usually bilateral, but frequently asymmetric

243

Why is establishing the chronicity of a 4th nerve palsy important?

Recent onset may be due to intracranial lesion and thus requires neurologic investigation

244

Which eye is preferred for fixation in a 4th nerve palsy?

Either eye (affected or unaffected)

245

Do unilateral 4th nerve palsies usually show a V pattern?

No, but bilateral 4th nerve palsies usually do show a V pattern

246

What are the clinical characteristics of a 4th nerve palsy?

1) ipsilateral hypertropia, 2) worse on contralateral gaze (overelevation in adduction), 3) worse on ipsilateral head tilt

247

In a patient with 4th nerve palsy with hyperdeviation <= 15 prism diopters in primary, what is the first approach to surgical treatment?

Weakening of ipsilateral IO (recession of contralateral IR can be added if > 15 prism diopters)

248

1mm of vertical rectus muscle recession results in what amount of vertical correction in primary gaze?

approximately 3 prism diopters

249

What are 2 options for surgical treatment of bilateral 4th nerve palsy?

1) Bilateral IO recession or 2) Harada-Ito procedure

250

What is the Harada-Ito procedure?

A procedure used to treat bilateral 4th nerve palsy that involves displacement of the anterior portions of the superior oblique tendons to a location adjacent to the upper edge of the lateral rectus muscle, about 8 mm posterior to that muscle's insertion. It improves deficient intorsion, but not the vertical deviation.

251

What can be used to differentiate IO paralysis from skew deviation?

Hypotropic eye should be intorted in IO paralysis, but extorted in skew devation

252

What 3 features can be used to differentiate IO paralysis from Brown Syndrome?

1) Forced ductions (negative in IO vs. positive in Brown), 2) strabismus pattern (A vs. V), 3) SO overaction (present vs. absent)

253

What are the clinical features of monocular elevation deficiency (formerly called double elevator palsy)?

1) hypotropia of the involved eye increasing in upgaze, 2) chin-up position, 3) fusion in downgaze, 4) ptosis or pseudoptosis

254

What are the 3 types of monocular elevation deficiency?

1) restriction, 2) elevator muscle weakness, 3) combination

255

What are indications for treatment of monocular elevation deficiency?

1) large vertical deviation in primary position, 2) abnormal chin-up position

256

What is a Knapp procedure?

Transposition of the MR and LR upward toward the SR. Can be used in the treatment of a monocular elevation deficiency

257

Hypoesthesia in what distribution, especially after local swelling has subsided, is a sign of orbital fracture?

the cutaneous distribution of the infraorbital nerve

258

What is an indication for urgent surgical intervention in orbital floor fracture?

evidence of restriction (which may be due to IR entrapment)

259

What is fixation duress?

Recession of the contralateral IR with or without the use of a posterior fixation suture to limit the contralateral eye in downgaze in a patient with orbital floor fracture.

260

What is the key feature of Duane syndrome?

Anomalous co-contraction of the MR and LR muscles, producing retraction of the globe in actual or attempted adduction.

261

Duane syndrome belongs what class of disorders?

Congenital cranial dysinnervation disorders

262

What are the 3 primary types of Duane syndrome?

1) poor ABduction with esotropia in primary, 2) poor ADduction with exotropia in primary, 3) poor ABduction and ADduction with or without horizontal deviation in primary.

263

What 3 points can be used to distinguish a (Type 1) Duane syndrome with poor abduction from a 6th nerve palsy?

1) globe retraction on adduction, 2) lack of correspondence between small esotropia in primary and large abduction deficit, 3) small-angle exotropia is found in contralateral gaze in Type 1 Duane, but not 6th nerve palsy

264

What surgical management can be used to minimize deviations and globe retraction in primary gaze in Duane syndrome?

Type 1: MR recession, Type 2: LR recession, Type 3: recession of both MR and LR

265

What is the presumed etiology of Brown syndrome?

abnormalities of the SO tendon-trochlea complex

266

What is a possible cause of acute-onset Brown syndrome?

sinusitis (may warrant CT in unexplained acute cases)

267

What are the primary clinical features of Brown syndrome?

1) deficient elevation in adduction that improves in abduction

268

What testing and result are required for the diagnosis of Brown syndrome?

positive forced duction testing demonstrating restricted passive elevation in adduction

269

What is appropriate management of mild Brown syndrome?

observation

270

When is surgery indicated for 6th nerve palsy?

if spontaneous resolution does not occur within 6 months of onset

271

What is the usual first operation attempted for correction of 6th nerve palsy?

MR recession and LR resection (if there is some residual LR function)

272

Which muscles are affected by thyroid eye disease (TED) in order of decreasing severity and frequency?

IR, MR, SR, LR

273

Is TED usually bilateral or unilateral?

Usually bilateral and asymmetric

274

What are the most common deviations seen in TED?

1) hypotropia, 2) esotropia

275

Should strabismus surgery be performed before or after orbital decompression in a patient with TED?

If orbital decompression will be needed, it should be performed before strabismus surgery

276

What is the natural history of CPEO?

onset in childhood with ptosis; slow progression to total paralysis of eyelids and EOMs

277

What percent of cases of myasthenia gravis have both ptosis and limited ocular rotations?

90%

278

After how long does ptosis usually worsen in a patient with MG asked to look upward?

after 30 seconds

279

Eyelid closure for what period of time will lead to temporary resolution of ptosis in a patient with MG?

20-30 minutes

280

Application of ice to the eyelids for how long will lead to improved levator and EOM function in a patient with MG?

2-5 minutes

281

What are three features distinguishing CPEO from MG?

1) Fatigability (seen in MG), 2) Response to Tensilon (seen in MG), 3) Diplopia (seen in MG)

282

What is Congenital Fibrosis Syndrome?

A group of congenital disorders in which EOM restriction is present and fibrous tissue replaces the EOMs

283

How can congenital fibrosis syndrome be distinguished from TED?

congenital onset in congenital fibrosis syndrome

284

What is Mobius syndrome?

A rare condition characterized by both 6th and 7th nerve palsies, resulting in abduction deficits and masklike facies, respectively.

285

How can esotropia results from high myopia?

High axial length can cause stretching and slippage of the lateral rectus pulley and supporting tissues, leading to esotropia

286

What can be performed to eliminate diplopia due to exotropia in INO?

MR resection and contralateral LR recession

287

What are potential etiologies for superior oblique myokymia?

aberrant regeneration of the 4th nerve or vascular compression of the 4th nerve

288

What are the clinical features of SO myokymia?

1) abnormal torsional movements causing diplopia and monocular oscillopsia

289

What is asthenopia?

A sense of ocular fatigue

290

What is a "hang-back" recession?

Suspension of a recessed tendon by sutures that pass through the thick stump of the original insertion rather than sutures passing through thin sclera.

291

What are the two primary means for "strengthening" a muscle?

1) resecting a portion of the muscle and putting it back together, 2) advancing the insertion of the muscle toward the limbus

292

What does the use of adjustable sutures involve?

Externalized sutures with slip knots, so that the position of a muscle can be altered during the early postoperative period

293

What are "Stay" or "Pull-Over" sutures?

Temporary (10-14 days) sutures attached to the sclera (at the limbus or rectus muscle insertion) brought out through the eyelids and secured to periocular skin to fix the eye in a selected position during postop healing.

294

What is a myotomy?

cutting across a muscle. It is used by some to weaken the IO.

295

What is a myectomy?

Removal of a portion of a muscle

296

What is a marginal myotomy?

Cutting partway across a muscle. It is usually used to weaken a rectus muscle further after a maximal recession.

297

What is a tenotomy?

Cutting across a tendon

298

What is a tenectomy?

Removing a portion of a tendon

299

For what purpose is a tenotomy or tenectomy usually used?

To weaken the SO

300

What is a muscle recession?

removal and reattachment of a muscle so that its insertion is closer to its origin. It is the standard weakening procedure for rectus muscles.

301

What is denervation and extirpation?

The ablation of the entire portion of the muscle within the Tenon capsule, including the muscle's nerve supply

302

For what purpose is denervation and extirpation used?

To weaken severely or recurrently overacting inferior oblique muscles

303

What is "recession and anteriorization?"

Movement of a muscle's insertion anterior to its original position.

304

For what purpose is "recession and anteriorization" used?

Used only on the IO to reduce its elevation function. Particularly useful in the presence of both IO overaction and DVD.

305

What is a posterior fixation suture?

An attachment of a rectus muscle to the sclera 11-18mm posterior to the insertion using a nonabsorbable suture; fixation to the muscle's pulley may be safer and equally effective.

306

For what purpose is a posterior fixation suture used?

To weaken a muscle by decreasing its mechanical advantage; often used in conjunction with recession; sometimes used in DVD, nystagmus, high AC/A esotropia and incomitant strabismus

307

What are the procedures that can be used to weaken the SO?

1) tenotomy, 2) tenectomy, 3) Z-lengthening, 4) functional lengthening (with silicone spacer, fascia lata, suture loops), 5) recession

308

Simultaneous surgery on how many rectus muscles can result in anterior segment ischemia?

2 or more, through disturbance of the anterior ciliary vessels running with the rectus muscles

309

What are the two primary types of incisions used in strabismus surgery?

1) Fornix incision (actually on the bulbar conj, but close to the fornix), 2) Limbal or peritomy incision

310

How long is a traditional fornix incision?

8-10mm

311

How long is a traditional peritomy incision?

120 degrees at the limbus

312

Induced astigmatism after strabismus surgery occurs most commonly in what situation?

surgery on 2 rectus muscles of 1 eye

313

How can successful strabismus surgery still result in diplopia?

Movement of the image of the fixation object in the formerly deviating eye out of a suppression scotoma

314

What is generally done if sclera is perforated and vitreous escapes through the perforation site during strabismus surgery?

Immediate application of local cryotherapy or laser therapy

315

What are the earliest signs of anterior segment ischemia due to anterior ciliary artery disruption in strabismus surgery?

AC cell and flare; more severe cases can be associated with corneal epithelial edmea, Descemet folds, irregular pupil

316

Which rectus muscle is most difficult to recover when it is lost during strabismus surgery?

MR

317

Which eyelid (superior or inferior) is more likely to be retracted or advanced during a vertical rectus muscle procedure?

Inferior

318

For what procedures is topical anesthesia not sufficient in EOM surgery?

pulling on a restricted muscle or attempting to expose a difficult to expose muscle

319

What form of topical anesthetic can be used for most EOM surgeries in cooperative patients?

tetracaine 0.5% or proparacaine 0.5%

320

What are the disadvantages of peribulbar or retrobulbar injections for EOM surgery?

these injected anesthetics may affect ocular alignment in the first few hours after surgery, which forces the surgeon to wait at least half a day to adjust adjustable sutures.

321

What is the oculocardiac reflex?

A slowing of the heart rate caused by traction on the extraocular muscles, particularly the MR

322

Can the oculocardiac reflex produce asystole?

Yes, in its most severe form

323

What is botox?

purified botulinum toxin type A

324

What is the mechanism of action of botox?

blockade of the release of acetylcholine at the neuromuscular junction, thereby paralyzing muscle

325

What is the time to onset of botulinum toxin action?

2-4 days

326

What is the duration of action of botulinum toxin in EOM and orbicularis?

5-8 weeks in EOMs, 3 months in orbicularis

327

In which situations is botulinum most effective in treating strabismus?

1) small to moderate angle esotropia and exotropia (<40 prism diopters), 2) postop residual strabismus, 3) acute paralytic strabismus (esp. 6th nerve palsy) to eliminate diplopia during recovery from palsy, 4) cyclic esotropia, 5) active TED, 6) supplement to MR recessions in large-angle infantile esotropia