Strabismus following posterior segment surgery MB Yadarola, M Pearson-Cody, DL Guyton Ophthalmol Clin N Am 17 (2004)

Incidence 3-60 % Scleral buckling under GA – % Under LA % Usually resolves in 3-6 months

Causes Mechanical Adhesions Explants Redirection of vectors Altered insertion Other 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