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Karen Grove, David Morrison; A comparison of inferior and medial rectus weakening by the faden procedure. Invest. Ophthalmol. Vis. Sci. 2013;54(15):4705.
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The faden procedure effectively weakens rectus muscles in their field of action. We frequently apply it to the medial rectus (MR) in high AC/A esotropia and to the contralateral inferior rectus (IR) in incomitant vertical strabismus. We anecdotally observed a greater effect on the latter. Given similarities of anatomy and dynamics of these muscles, this observation was not readily explained. Our aim was to assess for a difference in effective weakening of the inferior vs. medial rectus after faden procedure.
Surgeries performed by 2 Pediatric Ophthalmologists at an academic center between 1/2004 and 3/2012 were reviewed. 52 consecutive fadens with or without recession were identified. The effect was assessed by comparing pre-operative and post-operative deviation in the field of action of the operated muscle. An adjustment was made when faden was combined with recession. And when performed on bilateral medial recti, the total effect was halved: Faden effect Inferior rectus= (Δ Angle* Downgaze - Recession target angle). Faden effect Medial rectus= (Δ Angle* Near - Recession target angle) ÷ 2. *Δ Angle= pre-operative deviation - post-operative deviation. The primary result was alignment at post-operative month 2-3. Statistical comparisons were made using two-tailed unpaired Student’s t-test.
15 IR faden (3 without recession) and 26 MR faden (3 without recession) met criteria for inclusion. Mean age of the IR group was 42.3 ± 20.0yr, the mean age of the MR group was 6.2 ± 3.2yr. Mean follow-up in the IR group was 3mos (1wk to 15mos) and 17mos (1wk to 47mos) in the MR group. The mean effect of all fadens in the IR group was 9.2 ± 4.4 prism diopters (Δ) and 5.4 ± 3.4Δ in the MR group, p=0.009. The mean faden effect of combined faden with recession was 8.8 ± 4.4Δ in the IR group, and 5.1 ±3.3Δ in the MR group, p=0.02. Isolated IR faden effect was 11.0 ± 4.4Δ and isolated MR faden effect was 8.3 ± 3.6Δ, but not statistically significant, p= 0.46.
The IR faden had a 70% greater weakening effect than the MR faden. In considering traditional and more recent mechanical explanations of the faden procedure, we feel the active pulley hypothesis provides a more sound explanation of the faden and our findings. Further, our data suggest that the inferior rectus pulley suspension comprises a greater mechanical load than that of the medial rectus.
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