Strabismus Flashcards
EOM actions
- (1) primary actions of IR (depression) & SR (elevation)
- (1) the primary actions of the oblique muscles always involve TORSION
- mnemonic “SIN-RAD” to remember that Superior muscles IN-tort and Recti muscles AD-duct
- (2) secondary action of the obliques is OPPOSITE to their names (e.g. inferior oblique elevates)
- (3) tertiary action” either adduction or abduction.
IO
1) Excyclotorsion; 2) Elevate; 3) Abduct
SR
1) Elevation; 2) Intort; 3) Adduct
Bruckner
Bruckner compares the intensity and color of the red reflex. It may be altered in children with anisometropia and perfect alignment.
- shine a direct ophthalmoscope into both eyes to elicit a red reflex in both eyes simultaneously
- can also be used to identify lens opacities and moderate to severe anisometropia
- done mostly by PCPs to grossly detect strabismus.
ARC
The red-glass test is one of several methods to test for the presence of anomalous retinal correspondence (ARC). The test begins with measuring the patient’s deviation objectively with prism. A red glass is then placed over the non-deviating eye while the patient fixates on a white light. The patient is asked what he sees.
If the patient only sees one light, then suppression is present. If the patient sees the lights superimposed on each other (i.e. pink) despite a measurable deviation, then harmonious ARC is present. If the patient sees 2 lights but the separation between the lights is smaller than the measured deviation, then unharmonious ARC is present.
Correct Answer:
The area near the fovea has small receptive fields; therefore, objects need to be very similar in terms of size and shape to be fused properly (“central fusion”). Conversely, the peripheral retina has a large receptive field; thus objects can be more dissimilar in size and shape and still be fused (“peripheral fusion”).
EOM blood supply
IR & SR carry the bulk of the blood supply to the anterior segment.
Each rectus muscle has 1 to 3 anterior ciliary arteries (branches of the muscular arteries which themselves are branches of the ophthalmic artery).
Lateral muscular branch supplies: LR/LP, SR/SO
Medial muscular branch supplies: IR/IO, MR
infraorbital artery partially supplies the IR/IO
CN6 vs Duane’s
In CN VI palsy, there should be significant esotropia in primary position that is proportional to the severe limitation of abduction seen in this disorder.
In contrast, patients with Duane’s syndrome typically have only a small-angle (if any) esotropia in primary position.
Botox
BoTox injection usually paralyzes the muscle starting approximately 2-4 days after injection. It results in muscle lengthening with an effect lasting 5 to 8 weeks. This is in contrast to its duration when injected into the orbicularis muscle (e.g. for blepharospasm) where it lasts 3 or more months.
refractive accommodative esotropia
Subtype of Accommodative ET
Refractive (normal AC/A)
Usually measures?
high hyperopia (+3D to +10D)
Tx with full hyperopic correction
classic presentation:
(1) age of onset between 6 months and 7 years (average: 2.5 years);
(2) starts as intermittent esotropia and eventually worsens to constant esotropia;
(3) angle of deviation ~20-30 prism diopters;
(4) average hyperopia +4.00 diopters;
(5) equal deviation at distance and near fixation.
Pharm treatment high AC/A ratio
Long-acting cholinesterase inhibitors, like echothiophate iodide, can be used to suppress convergence in patients with a high AC/A ratio. In the case of accommodative esotropia, echothiophate (brand name: Phospholine Iodide) stimulates the ciliary muscle, thus reducing the central demand for accommodation which, in turn, reduces the excessive convergence of the eyes.
All physicians who prescribe this medication should inform the parents of the possibility of prolonged paralysis with any depolarizing general anesthetic like succinylcholine. Another side effect of this medication is iris cyst formation. These cysts can be prevented by co-administration of 2.5% phenylephrine.
TAO
This patient’s coronal section CT shows classic findings of TAO including widespread moderately enlarged recti muscles forming the muscle cone surrounding the optic nerve. This patient also has severe enlargement of the right medial rectus muscle and an alignment pattern consistent with severe restriction of the right medial rectus muscle. Extraocular muscle (EOM) enlargement and fibrosis in TAO classically causes a restrictive (not paretic) strabismus. In other words, a severely involved EOM in TAO will cause the globe to be pulled in the direction of that muscle (tethering effect) and the resultant restriction will be worse when the patient tries to look away from the restricted muscle. The antagonist muscle (in this case the right lateral rectus muscle) will appear weak due to the restriction of the involved muscle.
No surgery until deviation stable x 6 mo.
When correcting TAO, the surgical plan should NEVER involve resecting the antagonist to a restricted muscle. Making this mistake will lead to a failure to correct the strabismus and may actually worsen the patient’s motility. The only two answer choices that remain in this question after following the “no resection rule.” To maximize the effect of a recession for restrictive esotropia, one should choose the most restricted muscle (in this case the right medial rectus).
Finally just a few high yield tips for TAO questions on standardized tests. Patients can have TAO with any type of thyroid function (hyperthyroid, hypothyroid, or euthyroid). TAO patients should undergo orbital decompression before strabismus surgery before eyelid surgery. TAO patients should not be considered for strabismus surgery until they are out of the active phase of the disease and their alignment measurements are stable. There is no consensus for exactly how long measurements must be stable before considering strabismus surgery but 6-9 months of stability is a good general rule. For standardized testing purposes, never perform a resection for TAO strabismus.
In case you have forgotten how to read a strabismus alignment grid, please see the teaching diagram below.
EOM lengths
The active muscular portions of the medial rectus, superior rectus, lateral rectus, inferior rectus, and levator are 40 mm. The superior oblique has an active muscular portion of 32 mm. The inferior oblique has an active muscular portion of 37 mm. The muscles with the longest tendons are the superior oblique and levator with 26 mm and 14-20 mm, respectively. This makes the superior oblique the longest overall muscle and the levator the second longest. Because of its small tendon length (1 mm) the smallest overall muscle is the inferior oblique.
CN6 palsy
It is advised to wait a minimum of 6 months after cranial nerve VI palsy to see if any spontaneous resolution occurs. If the patient regains some lateral rectus function, then a large recession of the ipsilateral medial rectus along with lateral rectus resection is a good first operation. However in this case, there is still total paralysis and thus a muscle transposition operation is indicated.
Phoria
A latent deviation in which fusional control is always present
DVD
This patient demonstrates the classic findings of dissociated vertical deviation (DVD) which is present in more than half of congenital esotropia patients. DVD usually occurs after 2 years of age and can occur regardless of whether the original horizontal deviation was surgically corrected. DVD is not a true hypertropia since it violates Hering’s law. In the case of DVD, there is no corresponding downward movement of the opposite eye as the hypertropic eye moves downward to refixate.
tropia
A manifest deviation in which fusional control is not present.
Intermittent tropia
A deviation in which fusional control is present part of the time
Facultative suppression
This patient with intermittent exotropia demonstrates excellent stereoacuity, likely when his eyes are in the non-deviated state. Also, he does not complain of any double vision which indicates that he must be utilizing some suppression when his eyes are exotropic. This type of suppression is called “facultative suppression” since it only occurs when the eyes are deviated.
spasm of the near reflex
Patients who have spasm of the near reflex present with excessive convergence, accommodation, and miosis. These patients have normal ductions, but an abduction deficit on version eye movements.
A 21-year-old college student presents to your office for new-onset esotropia and diplopia symptoms. She states that this is finals week and needs to get her “eyes fixed” for her examinations. She measures 15 PD of ET at both distance and near. Her pupils measure 2 mm and do not constrict well to light. She has an abduction deficit OU on versions but full ductions OU. Which of the following most likely describes her condition?
Convergence insufficiency
X’ worse at near (exodeviation at near)*
usually age >10 years; F>M
Tx = orthopic exercise “pencil pushups” or base-out prisms to stimulate fusional convergence
You normally Rx XT with BASE IN in prism, but in this case, to help FIX the problem, base out prism is applied so that the patient has added strain and strengthens their convergence amplitude (“push-up”)
*remote near point of convergence (approx >10 cm) and there is an exophoria (not exotropia) at near fixation.
Monofixation syndrome
Peripheral fusion + central suppression (without bimacular fusion 2/2 macular scotoma).
Amblyopia stereoacuity:~ 200-3000 sec of arc. Small angle microtropia, usu ET (<8 Δ) Large angle latent phoria Suppression of distant target May have ARC Mediocre binocularity (peripheral only)
Causes: Surgically-corrected strabismus Anisometropia Primary monofixation syndrome Macular lesions
Tests?
Red glass, Worth-4-dot, Bagolini lenses, 4 Δ base-out test
ARC tests?
After image test, amblyoscope
Treatment?
Treat amblyopia
U/l vs b/l SO palsy
V pattern?
Unilateral: Rare
Bilateral: Common
Excyclotorsion?
Unilateral: 10deg
Head Position?
Unilateral: tilt to opposite side
Bilateral: tilt to weaker side and alternating hypertropia (RHT on L gaze and LHT on R gaze)
ET recession
A table listing the amount of bilateral recessions for an esotropia can be found in standard reference texts (as shown here). In general, one would perform 3.0 mm of bilateral recessions for 15 prism diopters of esotropia; 4.0 mm for 25 prism diopters; and 5.0 mm for 35 prism diopters.
Spiral of Tillaux
The “Spiral of Tillaux” describes how the rectus muscles insert progressively farther from the limbus. The mnemonic “M-I-L-S” describes this relationship with the medial rectus inserting closest to the limbus (~5.5 mm), followed by the inferior rectus (~6.5 mm), the lateral rectus (~6.9 mm), and the superior rectus (7.7 mm).
Also note that the temporal side of the vertical recti insert more posteriorly than the nasal side of these muscles.
Congenital vs Acquired CN4 palsy
Vertical fusional amplitudes?
Congenital: >10D (large)
Acquired: 3-6D (small)
Amblyopia?
Congenital: common
Acquired: rare
Compensatory head tilt: toward the contralateral shoulder and a gaze preference toward the side with the palsy
Harado Ito
Harado Ito–> split-to
This patient’s clinical presentation is most consistent with bilateral CN IV palsy. He is experiencing significant torsional diplopia, and as a result he is unable to fuse with prism. The torsion must be addressed surgically.
Due to the relatively large amount of excyclotorsion, a Harada-Ito procedure is indicated bilaterally. The Harada-Ito procedure involves splitting the superior oblique tendon and displacing the anterior fibers anteriorly and laterally to enhance incyclotorsion.
This type of situation (i.e. significant torsional diplopia) is relatively rare for patients with bilateral CN IV palsies. It is more common for these patients to present with hypertropia and inferior oblique overaction without significant torsional diplopia. In this situation, inferior oblique recessions/weakening is typically the preferred approach. This procedure typically has minimal impact on torsion however, and is not very effective for people who complain of significant torsional diplopia. Inferior oblique recession will sometimes reduce excyclotorsion by a few degrees, but generally does not have a major impact.
CN6 palsy
much more common in older children compared to at birth or during infancy.
For these patients, a face-turn is protective against amblyopia since this will produce a single binocular image. As many as 1/3 of these patients will have an underlying intracranial lesion that requires neuro-imaging.
It is important to check ductions in infants suspected of congenital CN VI palsy since, in the majority of cases, the child usually has congenital esotropia with cross-fixation simulating the abduction deficit.
Congenital ET
Infantile (Congenital) ET
Onset? before age 6 months (unlikely to improve spontaneously)
Family history of ET? Common
Amblyopia present?
NO (alternate or cross fixation)
Usually measures?
>30∆
Associated deviations?
IO Overaction, DVD usually after age 1 year, latent nystagmus
Cycloplegic refraction?
+1D to +2D hyperopia
Treatment?
Not best Rx: Prism glasses and alternate patching
Full cycloplegic refraction if >+2.50D then treat amblyopia then do surgery (early improves binocular vision. @ 4-6 mo)
Bilateral MR recession
If 2+ IOOA, weaken IO
If A or V pattern, then R+R with transposition (“MALE”)
IO strengthening
Strengthening of the inferior oblique requires reinsertion more posteriorly which predisposes the macula to greater danger should scleral perforation occur.
Null point with prisms. And surgery.
To reduce significant head turns in children with nystagmus, you orient the prisms so their apices are pointing toward the null zone. This effectively shifts the image into the null zone.
For this child, his null zone is in right gaze. Therefore, the prism over the right eye should be base-in while the prism over the left eye should be base-out.
For surgical correction of a head turn due to nystagmus, strabismus surgery is performed to rotate the eyes away from the null point.
Brown vs IO palsy
Both Brown’s syndrome and inferior oblique palsy will present with deficient elevation in adduction. However, the following characterize Brown’s syndrome: (a) positive forced duction testing; (b) V pattern; (c) and none or minimal superior oblique muscle overaction.
brown syndrome Rx: Partial (80%), not complete, tenectomy of the posterior portion of the superior oblique tendon helps avoid the complication of symptomatic superior oblique palsy. simultaneous ipsilateral inferior oblique weakening, or sewing inert spacer to cut ends of SO.
Inferior oblique palsy is characterized by: (a) negative forced ductions; (b) A pattern; and (c) superior oblique muscle overaction.
Knapp procedure
Procedure: In the absence of restriction, you can transpose the medial and lateral recti muscles to the superior rectus.
Indications for surgical treatment of monocular elevation deficiency include a large hypotropia on primary gaze and a chin-up head position.
Primary vs secondary deviation
primary deviation is the deviation that is measured when the normal eye is fixating (e.g. the left eye in this case).
The secondary deviation is the deviation that is measured when the paretic or restricted eye is fixating (e.g right eye here).
The secondary deviation is larger than the primary deviation since more innervational signals are required to bring the paretic eye into fixation (e.g. more innervation to the lateral rectus of the right eye in this case), which results in increased signals to the corresponding yoke muscle (e.g. the medial rectus of the left eye in this case) according to Hering’s law.
High myopia and muscle slippage
lateral rectus and result in esotropia.
Bangerter foils
Bangerter foils are a system of graded foils that are fit adhesively to glasses, much like Fresnel prisms. Foils are available in various levels of opacification (i.e. like neutral density filters), allowing the provider to control the level of blur in the non-amblyopic eye.
These are used with variable frequency among pediatric providers, but are potentially useful tools in patients with mild/moderate amblyopia who are intolerant of patching or atropine penalization.
Violates Sherrington and Hering’s law
What is Hering’s Law?
yoke muscles have equal innervation
violated by?
DVD
What is Sherrington’s Law?
muscle contraction accompanied by antagonist relaxation
violated by?
Duane syndrome: co-contraction of the medial and lateral recti occurs, resulting in globe retraction and lid fissure narrowing.
Possibly useful mnemonic: “Duane doesnt like sharing his DVD with Hering” –> helps to remember that Duanes violates Sherings Law, and DVD violates Herings Law.
CN4 palsy correction
Indications for surgical correction are: diplopia, persistent head tilt, asthenopia, and/or a significant vertical deviation.
IF < 15 prism diopters of vertical deviation
Rx: ipsilateral inferior oblique weakening is the procedure of choice.
IF > 15 prism diopters of vertical deviation
Rx: 1) recession of the contralateral inferior rectus + ipsilateral inferior oblique weakening
2) tuck SO tendon if significant tendon laxity is found.
3) ipsilateral superior rectus recession is often performed at the same time in both scenarios if forced duction testing shows limited depression on the side of the hypertropia.
