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

Mechanical Adhesions Explants Redirection of vectors Altered insertion Other Muscle injury Foveal misalignment Anisometropia Sensory disruption Causes

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

Strabismus following posterior segment surgery