SURGERY 369
the most diplopia. For torsion, may do Harada-Ito procedure (split SO, and advance the anterior/torsional half ). If deviation is worse up and nasal, then weaken the IO or resect SR. If it is worse down and nasal, then recess IR (if torsion is not a big problem), or tuck the SO (will have iatrogenic Brown’s syndrome).
ISOLATED SR PALSY Very rare; usually from orbital disease or superior blowout fracture.
SKEW DEVIATION Acquired, incomitant, supranuclear vertical deviation that is a diagnosis of exclusion. Rule out muscle, cranial nerve palsy, and myasthenia. See Chapter 8.
Surgery
STRABISMUS GENERAL PRINCIPLES Conjunctival incision may be fornix based (better cosmesis, often limited view), limbal (better view), or direct (Swan). Hook the IR from the nasal side, LR superior (don’t sweep broadly or may incorporate IO fibers), SR temporal (don’t get SO), MR superior and pass muscle hook in a tangential plane. Always clamp before cut, and generally use a spatulated needle with Vicryl suture.
ADJUSTABLE SUTURING Best for re-operations, TRIO, small angle deviations, or diplopic patients.
BOTULINUM TOXIN (BOTOX) Muscle injection to weaken the muscle that is antagonistic to the muscle causing the strabismus. Best for nonrestrictive strabismus, XT or ET < 40 pD; also small-angle strabismus, early postoperative over-/undercorrections, cyclic ET, and acute paralytic strabismus (muscle contraction begins within 6–8 weeks). Botulinum toxin type A binds to acetylcholine receptors on presynaptic motor nerve terminals and interferes with release of acetylcholine into the synaptic cleft.
Injected IM produces localized chemical denervation muscle paralysis within 2 days, lasting 5 to 8 weeks in EOM and 3 months in the orbicularis.
Do not exceed 200 units in 1 month. Use 0.1 cc for EOM injection and electromyogram (EMG) lead on the needle to localize the muscle; have the patient sit up afterward.
Side effects: 17% have ptosis or vertical strabismus complications; also diplopia and spatial disorientation. No systemic toxicity (injected dose is 1/100 of the toxic dose).
HORIZONTAL OFFSETS For hyperor hypodeviation; 1 pD ¼ 1 mm graded response.
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370 PEDIATRICS AND STRABISMUS
INFERIOR OBLIQUE MUSCLE (IO) SURGERY Weaken with myotomy or recession. Fibers are interspersed with orbital fat; thus, use care when bluntly dissecting (risk of adherence syndrome). Often has multiple insertions; use care to not disinsert the IR, and cut IO under direct visualization. Can cut it free, move IO to the border of IR (small recession), 3 mm posterior to IR (large recession), or anterior transposition.
SUPERIOR OBLIQUE MUSCLE (SO) SURGERY Isolate from the nasal side, but cut laterally (lies 4 mm posterior to SR insertion). Weaken with myotomy, tuck, or expander (may use 6 or 8 mm retinal band). Strengthen with resections (variable techniques) or tuck, which is good after scleral buckle procedure or multiple muscle procedures (does not compromise ciliary arteries) and for congenital palsy (usually has a long, floppy tendon); fold tendon, and place permanent suture.
STRENGTHENING PROCEDURES Resections increase the length-tension curve. Pass double-arm partial thickness suture in a ‘‘weaving’’ fashion through the muscle; two-loop locking pass at each side of muscle. Pull up muscle, cut tendon, measure forward, and reattach anteriorly, or cut section out of muscle and reattach at insertion.
TRANSPOSITIONS Several variations, including Knapp (two muscles, full tendon), Jensen (split muscle and suture together), and Hummelstein (take half of SR/IR and move lateral).
Harado-Ito procedure: anterior half of SO is torsional, posterior half is vertical, so split the tendon and advance the anterior half to the border of LR to enhance incyclotorsion.
A or V patterns: horizontal muscle offset changes the vector of forces and can correct up to 30 pD of and A or V pattern without significant IOO. Move MR toward the apex of the A or V, and move the LR the opposite direction a half tendon width to correct up to 15 pD (only if there is no oblique overaction).
WEAKENING PROCEDURES Recessions in effect ‘‘lengthen’’ the muscle, giving it more ‘‘play,’’ by moving its insertion more posterior. Pass a doublearm suture partial thickness through the muscle, in a ‘‘weaving’’ fashion, then do two-loop locking pass at each side of muscle. Pull up muscle, cut tendon, measure back, and reattach.
Marginal myotomy: Z myotomy, not accurate or often used; attenuates the length-tension curve.
Faden procedure: posterior fixation suture for nystagmus dampening, DVD, etc. The procedure ‘‘tacks’’ the muscle to the globe without moving tendon (changes the arc of contact in field of gaze, but not in primary gaze). Use permanent suture (Mersilene, etc.).
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SURGERY 371
STRABISMUS SURGERY COMPLICATIONS
Adherence syndrome: occurs if orbital fat is violated; not easily treated.
Anterior segment ischemia: short posterior ciliary arteries are compromised when muscles are disinserted, and the long posterior ciliary arteries are tasked more to provide blood supply to the anterior segment. Thus, usually do only two muscles at a time, as ischemia is likely to some degree after three-muscle surgery, even in young healthy eyes. May see cornea edema, Descemet’s folds, and iritis. Treat as iritis in general.
Astigmatism: usually with-the-rule and resolves within 6 weeks.
Conjunctival inclusion cyst: pale, nontender, cystic nodule; if excised, use caution, as cyst may extend deeply. May cause dellen.
Conjunctival scarring: usually from Tenon’s layer that was closed or reapproximated too close to the limbus, or plica semilunaris on the bulbar conjunctiva violated.
Eyelid changes: widening of palpebral fissure with SR or IR recession or narrowing of PF with SR or IR resection.
Foreign body granuloma: red, tender nodule from suture reaction.
Globe perforation: 1:100 incidence with scleral passes. Do a DFE intraoperative if you are suspicious of perforation, then cryotherapy or laser around the needle track. Usually benign unless there is VH, RD, or infection. Dilate all strabismus patients at one of the postoperative visits looking for the ‘‘snake eyes’’ (two holes) appearance of a perforation; if there are RPE changes around the site, then there is a low risk of any future complications and can tell patient it has scarred around the area.
Infection: preseptal or orbital cellulitis, usually within 72 hours.
Malignant hyperthermia: rare (incidence 1:6000–30,000) but carries a 10% mortality (historically 70%); triggered by succinylcholine or inhalational anesthetics (not local anesthetics). Ptosis, strabismus, and porphyria patients are at increased risk.
Earliest signs are tachycardia and increased end tidal CO2, then unstable blood pressure, tachypnea, sweating, muscle rigidity, cyanosis, dark urine (increased CPK in 2/3), and a rise in temperature later.
Treat with dantrolene 2–3 mg/kg up to 10 mg (muscle relaxant that stabilizes cell membranes and prevents release of calcium from sarcoplasmic reticulum); stop anesthetics, cool, hydrate and hyperventilate the patient with O2, and treat acidosis.
Pupil changes: IO surgery may damage parasympathetic fibers to the pupil.
Slipped muscle: diminished muscle function; can find it in its capsule and can usually reattach the muscle.
Lost muscle: can often find it against the orbital wall.
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372 PEDIATRICS AND STRABISMUS
Unsatisfactory alignment: can reoperate in 6 weeks; most cases of horizontal strabismus have a gradual trend toward exodeviation over many years.
Other
INFANT WITH DECREASED VISION Give a vision estimate (<20/70 normal, >20/200 legally blind), but avoid using the word blind with the patient’s parents. Check VF when older in order to counsel caretakers about the field of vision. Always give genetic counseling when appropriate (failure to do so is the leading cause of malpractice in pediatric ophthalmology).
Vision estimate: recognize parents (patient age 2–3 months when the fovea develops), OKN response ¼ at least 20/200, and reactive pupils are good signs. Poor vision signs include nystagmus (usually 20/200 or worse), wandering eye movements, staring at bright lights, oculodigital massage.
Usually a sensory anomaly, typically accompanied by a horizontal nystagmus and decreased VA. Etiology includes (mnemonic: NOSE):
Neurologic disease: cerebral palsy, anoxia, seizures, etc.
Obvious diagnosis on exam: cataract, glaucoma, aniridia, toxoplamosis scar, retinopathy of prematurity, ONH, optic atrophy, etc.
Subtle disorder: albinism, etc.
ERG abnormality: CSNB, achromatopsia, Leber’s congenital amaurosis
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