PRINCIPLES OF STRABISMUS SURGERY

PRINCIPLES OF STRABISMUS SURGERY

PG - Puneeth Isloor

Moderator Dr. Shubhashree Karat

ANATOMY AND ACTIONSEasy mnemonics SIN RAD and SLIM

MusclePrimary actionSecondary actionTertiaryActionSRElevationintorsionAdductionIRDepressionextorsionAdductionSOIntorsiondepressionAbductionIOExtorsionelevationAbductionMRAdduction - -LRAbduction - -

Blood supply Ophthalmic artery

Muscular arteries (2)

Medial .M.A Lateral .M.ASupplies MR,IR ,IO Supplies LR,SR,SO,LPS

anterior ciliary arteries - emerge on orbital surface from these muscular arteries - 10 -12 mm from the insertions

2 anterior ciliary arteries from all muscles except LR

The blood supply of IO muscle enters it just lateral to IR this neurovascular bundle can get disinserted while recessing IO

CONCEPT OF ARC OF CONTACTThe point at which the tendon first touches globe Tangential point

The arc of contact is distance between the tangential point and the centre of anatomic insertion of the muscle

MR 6 mm , LR 15 mm , SR-8.4mm, IR-9mm

Power of a muscle is proportionate to its arc of contact hence recession weakens muscle by reducing arc

When a muscle contracts , it produces a force that rotates the globe

The rotational force length of the moment arm (m) rotational force force of muscle contraction (F) Rotational force = m F

General goals of strabismus surgeryTo restore binocular visionTo improve ocular alignmentTo enlarge the field of single binocular visionTo alleviate an abnormal head postureTo improve the aesthetic appearance of patient

Goals should be prioritised based on the cause of strabismus.

PRE-OPERATIVE ASSESSMENTHistory Rule out neurological diseases - Previous family photographs(FAT) - Document time of onset of strabismus - Past anesthestic complications and bleeding diatheses -Past history of trauma -Past history of strabismus surgery elsewhere

Pre op Examination Look for nystagmus , anomalous head postureLid abnormalities epicanthus ,ptosis,telecanthusVisual acuity recordingCycloplegic refractionAnterior segment Look for conjunctival scars,blebs - Scleral buckle, scleral ectasia Fundus Macular pathology , Chorioretinal scarring

Identify if eccentric fixation is presentTest for ductions and versions and vergencesFDT and FGT in adults pre-operativelyOrbital imaging only in case of thyroid myopathy and slipped or lost muscle .Not routinely done.

Anesthesia GA - LA in adults Sub tenons is preferred.

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ANATOMICAL CONSIDERATIONS GENERAL PRINCIPLES

Distance of each rectus muscle from limbus must be taken into consideration.

The muscle insertions at new locations must be splayed and not narrow otherwise central sag occurs.

While performing vertical transpositions of horizontal recti ,care should be taken to keep the muscle shift concentric to limbus.

Never operate on 3 muscles at once to reduce risk of anterior segment ischemia

Sclera is thinnest at insertion site of recti .Hence 0.5 mm stump of muscle should be left for resection re-suturing

Avoid damage to vortex veins and tenons during supramaximal recessions involving posterior sclera

Establish symmetry between two eyes if it doesnt exist and maintain it when it exists.

In patients with high grade stereopsis , caution while operating on SO as it could induce vertical diplopia

INCISION TYPES Fornix incision Limbal incision

Fornix approach - Preferred for surgery of oblique muscles - Made at a point 8- 9 mm from the limbus

Advantages - Access to more number of muscles at a time -More patient comfort -Less scarring -Ease of construction and closure

Disadvantage For large resections cannot resect conjunctiva - Cannot approach posterior orbit if needed - Increased risk of conjunctival tear

Made at 8-9 mm to avoid extraconal pad of fat which begins at 10 mm from limbus

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Limbal incision Used for rectus muscle surgeries

One must be careful not to include the plica seminularis at medial end and not to include the lateral canthus to prevent symblepharonTenon s capsule should not be sutured with the conjunctiva can lead to unsightly hyperemia

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Strabismus surgery corrects ocular misalignment by at least 4 different mechanisms - Slackening a muscle - Recession -Tightening a muscle Resection , plication -Reducing moment arm Faden procedure -Changing vector force by transposition

STRABISMUS SURGERIESWEAKENING PROCEDURES OF RECTI

STRENGTHENING PROCEDURES OF RECTI

WEAKENING PROCEDURES OF OBLIQUES

STRENGTHENING OF SUPERIOR OBLIQUE

WEAKENING PROCEDURES OF RECTI MUSCLES 1)Conventional recession 2)Hang back recession 3)Adjustable suture technique 4)Retroequatorial myopexy (Faden) 5)Recession of vertical recti 6)Slanting recession 7)Marginal myotomy and myectomy

6 mm for medial rectus and 8 mm for lateral rectus. 5mm and 10 mm as per dad(lol).A recession of less than 3 mm for MR and 4 mm for LR are ineffective.18

1.CONVENTIONAL RECESSIONPrinciple Moves the muscle insertion CLOSER to the ORIGIN creating a muscle slack

The muscle slack reduces muscle strength as per starling s length tension curve

It does not reduce the moment arm when eye is in primary position

The muscle should be re-inserted within the length of its arc of contact

Hence , there is maximum limit up to which a recession can be done for each muscle

6 mm for medial rectus and 8 mm for lateral rectus. 5mm and 10 mm as per dad(lol).A recession of less than 3 mm for MR and 4 mm for LR are ineffective19

A recession has its greatest effect in the field of action of the muscle.

On rotation of eye away from recessed muscle , 2 things happen - Recessed muscle slack is reduced

- The recessed muscle is inhibited by reciprocal inhibition(Sherrington s law)

ProcedureAnesthesiaLids retracted by self retaining speculumFDT done

Limbal conjunctival incision is made and two radial incisions made at the ends of the limbal incision

The intermuscular septum is button holed

The jameson s hook and the green s hook are passed underneath the muscle

Check ligaments and intermuscular septum are separated

2 interlocking loops of 6-o vicryl are passed at the two ends of muscle insertions

Muscle is cut with tenotomy scissors leaving a stump of 0.5 mm

Measurement of recession is made with callipers and the recessed muscle is sutured at the new site

2 .HANG BACK RECESSIONPrinciple -Suspends the muscle back, posterior to scleral insertion , with a suture to weaken the muscle.

Small to medium sized recessions of 3- 6 mm can cause overcorrection because of central muscle sag

Indications - A supramaximal recession is needed but unable to pass suture posteriorly due to risk of scleral perforation

- Recession over a retinal buckle

- Recession over an area of scleral ectasia as in high myopes

- Large recession of a tightly contracted muscle

Advantage Needle passes through thick anterior sclera and excellent exposure

Disadvantage Narrowing of muscle insertion causing central muscle sag

To reduce narrowing of muscle insertion and central muscle sag , there is hemi hang back recession in which the sutures are passed through scleral tunnel and then inserted.26

3. ADJUSTABLE SUTURE TECHNIQUE Principle Here recession allows fine tuning of ocular movements in the immediate post-op period

Procedure -Performed in 2 stages1st stage GA or LA .Recessed muscle is sutured such that the sutures can be made loose and muscle recession can be varied.

2nd stage Readjustment is made within 24 hours of the first surgery under local anesthesia.

The adjustments can be made using a bow-tie knot or by a sliding noose

Not recommended for children less than 15 years of age as it needs cooperation for adjustment stage.

Indications - Large angle strabismus where results are inconsistent - Paralytic strabismus - Restrictive diseases Thyroid myopathy - Previously injured extra-ocular muscles where muscle function assessment may be inaccurate

4. RETROEQUATORIAL MYOPEXY(FADENS)Principle -The muscle is sutured posterior to its insertion farther than the limit of its arc of contactIt shortens the lever arm

It reduces the moment arm only when the eye rotates towards the muscle sutured.

It is usually combined with a muscle recession as its weakening effect alone is not much

Best suited for MR as it has the shortest arc of contact Works the least with LR as it has a long arc of contact

Measurements for various muscles - MR 12- 14 mm - LR - 16-20 mm - SR and IR 14-16 mm

Indications for a Faden - Paralytic strabismus In case of a LR palsy ,Faden of the contralateral MR is done .

Used when patient is orthotropic in primary position but has diplopia on gaze towards paretic muscle.

- Duane s retraction - Contralateral MR - DVD Superior recti - Nystagmus blockage syndrome MR

When combining with a recession , the muscle must be fixed at a distance obtained by subtracting the Amount of recession from the total faden.

In a right LR palsy , there is excessive impulse to Right LR and left MR by herring s law. So on right gaze, there is left eso. Hence we can do a faden of the left MR along with recession of right MR. Same holds good for duanes retraction.34

5. RECESSION OF VERTICAL RECTI

Principle The check ligaments for the vertical recti are linked to whitnall s ligament for SR lockwoods ligament for IR

Hence ,While recessing IR ,care must be taken to separate it from lockwood s ligament and to prevent lower lid retraction

Indications- - DVD - Thyroid myopathy -Congenital fibrosis

Does not exceed 5mm in these 3 indications

6. SLANTING RECESSIONSFor esotropia,A- pattern : both MR recessed with Upper end> lower endV-Pattern : Both MR ..lower end > upper end

Difference of 3-5 mm between the upper and lower ends

For exotropia,A-Pattern : Both LR Lower end > upper endV Pattern : Both LR .Upper end > Lower end

7.MARGINALMYOTOMYPrinciple -Several cuts are made alternatively at the two borders of the muscle.

Indication To weaken a muscle that has been maximally recessed

They are transverse cuts in the muscle of atleast 2/3 width.

MYECTOMY used only for inferior oblique

WEAKENING PROCEDURES OF RECTI

STRENGTHENING PROCEDURES OF RECTI

WEAKENING PROCEDURES OF OBLIQUES

STRENGTHENING OF SUPERIOR OBLIQUE

TIGHTENING PROCEDURES ON RECTI ResectionAdvancementDouble-breasting or tuckingTransposition of adjacent muscles

1.RESECTIONIt is the most common procedure for strengtheningInvolves excision of the tendinous part onlyIf excess resection is done , it will weaken the muscleHence For MR maximum limit is 6 mm For LR - maximum limit is 8mm

The minimum limits for MR and LR is 3 and 4.5 mm respectively for it to be effective.40

ProcedureAnesthesiaLids retracted by self retaining speculumFDT done

Limbal conjunctival incision is made and two radial incisions made at the ends of the limbal incision

The intermuscular septum is button holed

The jameson s hook and the green s hook are passed underneath the muscle

Check ligaments and intermuscular septa are separated

Measurement of the resection is marked with calipers ensuring that the muscle is not stretched

Two double armed vicryl 6-0 sutures are passed through muscle in an interlocking fashion

A muscle clamp is applied 2 mm distal to sutures and the greens hook removed and muscle is resected and cut leaving 0.5 mm stump

Conjunctiva is re-apposed

2. ADVANCEMENT Principle- The muscle is re-inserted closer to limbus , thus making it more taut - increases arc of contact

Indications - It is the ideal choice in a squint where recession has been done earlier - In paralytic squint , advancement may be combined with resection

3. DOUBLE BREASTING OR TUCKINGPrinciple -It shortens the muscle by folding the muscle and suturing the folded muscle to muscle.

Indications -Commonly used for plication of the superior oblique muscle in superior oblique palsy.

The length of the tuck ranges from 6-12mm

Advantages over resection Muscle is not disinserted and anterior ciliary vessels are not compromised It is reversible

4.MUSCLE TRANSPOSITIONSIndications - Paralytic strabismus - Slipped or lost muscle Various procedures are Knapp s procedure - Jensen s procedure -Hummelsheim procedure

KNAPP S PROCEDURE Indications -Double elevator palsy -Lateral rectus palsy

MR and LR muscles are transposed superiorly to the insertion of SR muscles

A large posterior dissection is needed to separate it from the intermuscular septum and check ligaments

JENSEN S PROCEDUREIndications Lateral rectus palsy

Here the adjacent muscles are tied together 12 mm posteriorly, but not disinserted

Lateral halves of SR and IR are dissectedUpper and lower halves of LR are dissected

Lateral half of SR and upper half of LR are suturedLateral half of IR and lower half of LR are sutured

ADVANTAGE Less chance of A/S ischemia

HUMMELSHEIMS PROCEDUREIt is a split tendon transfer technique to preserve anterior ciliary artery perfusion

Indications - Lateral rectus palsy - Lost medial rectus muscle

Lateral halves of SR and IR are dissected upto 14 mm from their insertion

They are reinserted adjacent to LR insertion and they should touch the LR insertion

Two modifications of the Hummelsheim are

1)Augmented Hummelsheim Brooks Augmentation by resecting 4-6mm of transposed recti It tightens the transposition.

Muscle union modification (Foster modification) Transposed and paretic muscles are sutured together and then to sclera , 4mm posterior to insertion.

Other transposition procedures

1)Callahan s procedure Modification of jensen s procedure used for elevator palsy.

Upper half of MR ----sutured to ---medial half of SRUpper half of LR ----sutured to----lateral half of SR

2)OConnor s procedure Here transposition of Vertical recti to LR is combined with LR tucking

5. VERTICAL TRANSPOSITION OF HORIZONTAL RECTI IN A-V PATTERNS WITHOUT OBLIQUE DYSFUCNTION

For A Pattern For V PatternMR shifted up(BE) MR shifted down(BE)LR shifted down(BE) LR Shifted up (BE)

MR up ,LR down in MR down ,LR up monocular recession -resection

WEAKENING PROCEDURES OF RECTI

STRENGTHENING PROCEDURES OF RECTI

WEAKENING PROCEDURES OF OBLIQUES

STRENGTHENING OF SUPERIOR OBLIQUE

WEAKENING PROCEDURES OF INFERIOR OBLIQUE

Indications 1)Superior oblique palsy (Ipsilateral IO)2)V pattern with IO overaction (Both eyes IO)3) Double elevator palsy (Contralateral IO)4)Dissociated Vertical deviation

Four Procedures1)Inferior oblique Recession 2)Anterior transposition with graded recession3)Extirpation-denervation 4)Inferior oblique myectomy

In Fink s method - For a 8 mm recession of IO , a point 6 mm inferior and 6 mm posterior from the inferior end of LR insertion is chosen as the anterior point and another point 5-6 mm posterior to it in the same meridian For a 10 mm recession , the anterior point is 2 mm below the 8 mm point along the course of muscle For a 6 mm recession , the anterior point is 2 mm above the 8 mm point along the course of muscle 58

1)Inferior oblique recession - is of 2 types - Fink s method - Produces only slackening

- Park s method Produces slackening plus mild anterior transpositioning The IO is inserted at a point 2mm lateral and 3 mm posterior to lateral end of IR insertion

2)Graded recession - Anterior transpositionRecommended by Kenneth Wright for IO overactionThe basis is that the more anterior the IO insertion , the greater the weakening effect

The more anterior the placement of IO insertion , the more the muscle becomes a depressor

Complication of this procedure is the postoperative limitation of elevation called The anti elevation syndrome

Overaction I .O Placement+14mm posterior and 2 mm lateral to IR insertion+23mm posterior to IR insertion+31-2mm posterior to IR insertion+4At IR insertion

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3)Denervation and extirpation The nerve to IO is on posterior border of the muscle . It can be hooked and cauterised It results in laxity of muscle. Can be combined with myectomy

Strengthening procedure for IO are limited as it lacks a tendinous portion and hence resection cannotg be done. Double breasting can be tried.61

4) Inferior oblique myectomyIt is faster to perform and does not need the muscle to be sutured to the sclera less risk of perforationMuscle is allowed to retract into the tenon s capsule and the conjunctiva is closed

IO strengthening procedures are rare . Used in treatment of incyclotorsion occuring after macular translocation surgery. Tucking of the inferior oblique can be done here.62

WEAKENING PROCEDURES OF SUPERIOR OBLIQUE

They are two in number 1) Superior oblique tenotomy 2)Superior oblique tendon expander of Wright

Indications for both Brown syndrome

Approach to SO Through fornix incision

1.SUPERIOR OBLIQUE TENOTOMY Should be performed nasal to SR muscle

A temporo-conjunctival incision is made and reflected nasally This helps in many ways

1)To keep the nasal intermuscular septum intact and reduce tendon scarring down to sclera

2)To reduce the incidence of post operative SO palsy which occurs with temporal tenotomies (because they scar down to sclera)

2)SUPERIOR OBLIQUE TENDON EXPANDER OF WRIGHT

Principle : Controls the separation of the ends of tendon, allowing quantification of tendon separation

A segment of silicone 240 retinal band is inserted between the cut ends of SO tendon .

The first suture is placed 3 mm nasal to the superior rectus

The maximum length of band is 7mm.Most can be managed with 5-6mm length of band.

WEAKENING PROCEDURES OF RECTI

STRENGTHENING PROCEDURES OF RECTI

WEAKENING PROCEDURES OF OBLIQUES

STRENGTHENING OF SUPERIOR OBLIQUE

SUPERIOR OBLIQUE MUSCLE STRENGTHENINGSO can be functionally divided into - Anterior 1/3 Intorsion - Posterior 2/3 Depression and abduction

Best accessed through fornix incisionMainly two procedures 1)Harada-Ito Procedure 2)Superior Oblique tendon tuck

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1.Harada Ito procedurePrinciple -Tightening the anterior fibres will induce intorsion without too much change in depression and abduction.

Indication - a partially recovered SO palsy where there is only large degree of extorsion

It is of 2 types -1)Fells modificied Disinsertion technique anterior fibres are disinserted and moved anteriorly and laterally

then sutured at 8 mm posterior to superior border of LR insertion

-2)Classic Harada Ito here the fibres are looped with a suture and displaced laterally

2. Superior Oblique tendon tuckIndications Usually done for congenital superior oblique palsy Also for traumatic superior oblique palsy

If too tight a tuck , then iatrogenic browns syndome is seenAvoided by doing intraoperative FDT

COMPLICATIONS OF STRABISMUS SURGERY

INTRAOPERATIVEPOST-OPERATIVEOperation of wrong eye and wrong muscleOrbital cellulitis HemorrhageSuture granulomasScleral perforationConjunctival cystsCentral sag DellenMuscle sheath ,tendon rupture and fat prolapseOver correction and undercorrectionLoose sutures in the muscleVomitingSlipped or lost muscleAnterior segment ischemia

LOST MUSCLE OR SLIPPED MUSCLEMost commonly affects MR and is difficult to retrieve

MR has no fascial connections to obliques to prevent it from retracting posteriorly

Can occur if the muscle slips during disinsertion and if the sutures have not been applied correctly A slipped muscle occurs when a muscle retracts posterior to the intended recession

Lost muscle can also occur after orbital trauma or hemorrhage

It occurs if the sutures have been applied to anterior tenons instead of muscle tendon,so the muscle slips posteriorly while a pseudotendon ofConnective tissue remains attached to sclera75

Signs of lost muscle -Limited ductions -Widening of lid fissure in the field of action of muscle

Management - Find the muscle and surgically advance it to anterior sclera - If not retrieved , then a transposition procedure must be performed Hummelsheims for MR.

ANTERIOR SEGMENT ISCHEMIA-Rare , but serious complication

-Occurs if 3 or more recti surgery are done at a time especially in adults with atherosclerosis and hyperviscosity

-Occurs in cases with previous radiotherapy and previous RD surgeries

-Two vertical recti should not be operated with one horizontal rectus and especially the LR

-The obliques do not contribute much to this

SignsCorneal edemaCorneal thinningSevere anterior uveitisIris atrophyDistorted pupilCataract and phthisis in late stages

Treatment Steroids local and systemic

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