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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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