Minimally invasive strabismus surgery (MISS) for inferior obliquus recession

All consecutive patients needing inferior obliquus recessions operated on by the author between December 2006 und December 2007 were included. In the same time period, a proportion of inferior oblique recessions was performed by another surgeon in a conventional matter. The author is not aware that this has introduced bias, since surgeries were distributed between the two surgeons by availability in the operating theatre. Usually, patients with fourth nerve palsies were treated with a superior oblique tuck or combined inferior oblique recession and superior oblique tuck. Fourth nerve palsies with rather comitant and not too large angles in adduction were treated with isolated inferior rectus recessions.

Patients necessitating simultaneous superior obliquus or vertical rectus surgery or whose inferior oblique muscle was already previously operated on. All patients had at least one complete orthoptic examination 5 days before the surgical procedure, on the first postoperative day, and after 6 months (range 5–7 months) at the Department of Strabismology and Neuro-Ophthalmology, Kantonsspital, St. Gallen, Switzerland. The following parameters were registered: deviation in primary position and in 25° of adduction for a near target, head posture, field of binocular single vision, motility, stereovision, visual acuity, refraction, lid and conjunctival swelling and redness, and number and types of complications. Abnormal head posture was estimated while the patient was looking at an accommodative target at 33 cm. Binocular single vision was measured using Bagolini's striated glasses and, if possible, using Harms' tangent screen [15]. Stereovision was measured in an ordinal scale with following tests: two-pencil test, Titmus stereotest, and TNO-test. For the two plate tests, values were registered in arcsec. For analysis, each patient was categorized as “improved”, “same”, or “worse”. Since many patients were too young to allow an adequate measurement while fixating at a distance target, only deviations while looking at an accommodative target in 33 cm were included. Of 17 patients eligible for the study, 15 (88%) could be included. Two patients were excluded since they did not come back for the 6-month follow-up visit. None of them had an intraoperative or immediate postoperative complication. Conjunctival and lid swelling was determined on the first postoperative day using a previously used grading system developed for horizontal rectus muscle surgery [16]. The scale of conjunctival and lid swelling and injection ranges from 0 to 3 (0 meaning absent, 1 mild, 2 moderate, 3 strong).

Surgery is performed using the operating microscope under general anesthesia. All surgical steps can be performed without an assistant. The amount of recession corresponded to the vertical deviation determined in 25° of adduction. For each millimeter of recession an anteralization of 1/3 of a millimeter was performed, which makes it possible to reattach the anterior border along the physiologic course of the muscle. Preoperatively, no eye drops were given. Directly before surgery, the eyelids and the skin surrounding the operative site were disinfected with Betadine® (Iodum 10 mg ut povidonum iodinatum excip. ad solute. pro 1 ml). The conjunctiva was not rinsed. A limbal traction suture (Silkam® 6-0 or Safil® 6-0 BV-1) is applied in order to expose the temporal inferior quadrant of the eye globe. During surgery, a direct contact of the traction suture with the cornea has to be avoided. A 4 mm radial cut is performed over the insertion of the inferior obliquus muscle (Fig. 1a). The anterior margin of the cut is 1 mm anterior of the tendon insertion. In patients with reduced elasticity of the conjuntival tissue, a slightly larger opening will be needed. A second cut is applied where later the reinsertion will be performed. If the reattachment will be next to the lateral border of the inferior rectus muscle, the muscle itself will help as a landmark. If a graded recession of a certain amount is planned, the place is marked using a measure caliper. With blunt Wescott scissors, the inferior obliquus inseration is separated from the surrounding tissue (Fig. 1b). Then, using the same scissors, the insertion is completely detached (Fig. 1c). Now, one single suture (Vicryl® 7-0 GS-8) is applied to the anterior third of the detached muscle insertion (Fig. 1d). In this patient series, only the anterior border was reinserted to the sclera, and therefore no second posterior suture was used. Afterwards, a blunt cannula (Hurricain Medical, 20G x 1 in. Sub-Tenon's Anaesthesia Cannula) is passed through the second cut, the reinsertion site opening, and advanced in order to get out through the first cut (Fig. 1e). The needle is gently inserted in the cannula until it is fixed (Fig. 1f). Now, the cannula is retracted (Fig. 1g). After withdrawal of the needles from the cannula, the scleral fixation is performed (Fig. 1h). After having controlled that all posterior fibers of the inferior obliquus insertion have been properly cut, the surgical procedure is finished by applying single sutures (Vicryl® Rapid 8-0 GS-8) to each of the two small cuts (Fig. 1i). At the end of surgery, TobraDex® ointment (1 mg dexamethasone and 3 mg tobramycin per g, 0.5% chlorobutanol) or Maxitrol® ointment (polymyxin B sulphate 6,000 units, neomycin sulphate 3,500 units, dexamethasone 1.0 mg, methylparaben 0.05%, and propylparaben 0.01%) was applied. There was no need for an eye patch. For the first 2 weeks after surgery the following treatment was prescribed: TobraDex® suspension (1 mg dexamethasone and 3 mg tobramycin per ml, 0.01% benzalkonium chloride) t.i.d. and TobraDex® ointment in the evening or Maxitrol® suspension (polymyxin B sulphate 6,000 units, neomycin sulphate 3,500 units, dexamethasone 1.0 mg, and benzalkonium chloride 0.004%) t.i.d. and Maxitrol® ointment in the evening. If during minimally invasive surgery the operating site needs to be better visualized, e.g. if excessive bleeding occurs, which cannot be stopped with cautery through the small cuts, the two openings can be joined (Fig. 1J).