Transcript Strabismus following posterior segment surgery

Strabismus following posterior
segment surgery
MB Yadarola, M Pearson-Cody, DL
Guyton
Ophthalmol Clin N Am 17 (2004) 495-506
Incidence
• 3-60 %
• Scleral buckling under GA – 4 -11 %
• Under LA 15 - 43 %
• Usually resolves in 3-6 months
Causes
Mechanical
Other
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Adhesions
Explants
Redirection of vectors
Altered insertion
Muscle injury
Foveal misalignment
Anisometropia
Sensory disruption
Mechanical Adhesions
• Usually due to violation of Tenon’s capsule
• ‘Fat adherence syndrome’
Explants
• Sponge can tighten muscles
• Changes in oblique muscle action leading
to vertical and torsional misalignment
Muscle/Nerve injury
• Rupture of muscle from aggressive cryo
• Excessive stretching causing fibrosis
• Direct injury to nerve, particularly after the
muscle has to be disinserted
Anesthetic myotoxicity
• Anesthetic myotoxicity causes initial
paresis and later fibrosis
• Most commonly hypotropia, limited
elevation, V pattern and extorsion
Anesthetic myotoxicity
• Initial paretic phase lasts upto 2 months
• Later overaction is more common
following segmental fibrosis
• Extensive fibrosis causes restrictive
pattern
• Hyaluronidase decreases anesthetic
myotoxicity
Foveal misalignment
• Limited Macular repositioning can lead to
diplopia in 5.2 %
• Dragged fovea diplopia syndrome
Altered fusion
• Poor vision
• Anismetropia / aniseikonia secondary to
aphakia, silicone oil
• Axial myopia induced by buckle
Evaluation
• Should include 9 gaze measurements
• Primary / secondary deviations
• Assessment of torsion
Indirect ophthalmoscopy
Lancaster red-green charts
double maddox rods
amblyoscope
• Assess fusion
Evaluation
• Look for epiretinal membranes
• Amsler grid testing
• Lights on-off test
Surgery
• Standard tables not applicable
• General anesthesia preferred
• FDT done at all stages of surgery
• Before and after muscle disinsertion
• After lysis of adhesions
• After repositioning of muscles
• Leave buckle in place, unless it is the
direct cause of scarring
Surgery
• Resections as single procedure in
restrictive strabismus avoided
• If buckle capsule is well formed, then treat
it as the secondary insertion of the muscle
• If buckle exposed, irrigate with antibiotic
solution
Surgery
• Cut end of the muscle kept in contact with
sclera, either posterior or central to the
buckle
• Hang-back recession performed with 6-0
polyester
• If superior oblique tendon is misdirected
by the buckle, excise the buckle locally
Surgery
• When sup. obl. Is damaged resulting in
extorsion and hypertropia – modified
Harada-ito procedure
• In significant scarring, operate on the other
eye
• Consider conjuntival recession if conj. is
shortened / scarred
Other measures
• Adjunctive botox
• Prisms – can also identify dragged-fovea
diplopia
• Occlusion with clear nail polish, Scotch
Satin tape, opaque contact lens
Preventive measures
• Subtenon’s block
• Avoid excessive dissection, orbital fat
• Avoid excessive tension on muscles
• Pass buckle inferior to superior oblique
tendon