A Quantitative Inferior Oblique Traction Test: Clinical Applications
Stephen P. Kraft, MD; Alan Connor, FRCOp
Department of Ophthalmology and Vision Sciences, The Hospital for Sick Children
Toronto, Ontario, Canada
Introduction: We describe an inferior oblique (IO) traction test (IOTT) to gauge IO stiffness before and after IO myectomy (IOMy). We determined if IOTT correlated with pre-operative IO overaction (IOOA), and whether eyes with IOOA have stiffer muscles than control eyes.
Methods: We performed a 10-year retrospective chart review for IOMy and intra-operative IOTT by a single surgeon. Under anaesthetic, we determined the number of ‘clock hours’ of ‘intorsion freedom’ (nearest 0.5 hr.) We compared the clock hr. of freedom before and after 10 mm. IOMy. We correlated IOTT at start of surgery with pre-operative IOOA (scale 0 to +4) in 56 myectomies (43 patients) and compared it to control group of 23 eyes (15 patients) with minimal/no IOOA.
Results: Mean intorsion freedom in the operated eyes was less than in control eyes (1.63 vs 1.89 clock hr.; p<0.005). There was an inverse relationship between IOOA and IOTT (Pearson rank coefficient, r = -0.45; p<0.001). IOMy produced mean 1.32 clock hr. increase in freedom (range 1.0-2.5 hr.). All 5 double-bellied IO muscles also showed minimum 1 clock hr. change (range 1.0 to 1.5 hr.) after myectomy of the anterior belly.
Discussion: IOTT confirmed that overacting IO muscles have significantly greater stiffness than control eyes. IOOA grade predicted the degree of IO stiffness at surgery. Finally, although IOMy creates at least 1 hr. of increased intorsion freedom, IOTT cannot rule out presence of second belly.
Conclusion: IOTT after IOMy does not substitute for careful inspection to ensure no IO fibers remain.
References: 1. DeAngelis D, Makar I, Kraft SP. Anatomic variations of the inferior oblique muscle: a potential cause of failed inferior oblique weakening surgery. Am J Ophthalmol 1999;128:485-8.
2. Guyton DL. Exaggerated traction test for the oblique muscles. Ophthalmology 1981;88:1035-9.|3. Jung JH, Holmes JM. Quantitative intraoperative torsional forced duction test. Ophthalmology 2015;122:1932-38.