Session: Free papers Session VI - Vertical Strabismus

Inferior Oblique Anterior Nasal Transposition (IOANT) effect on vertical, torsional and horisontal alignment - our first 86 cases

Introduction

The inferior oblique anterior and nasal transposition (IOANT) is a surgical technique used in patients with fourth nerve palsy exhibiting significant torsional and/or vertical deviation, along with substantial inferior oblique muscle overaction (IOOA). This technique involves transfer of the inferior oblique (IO) nasal to the inferior rectus muscle. Our study aims to assess the impact of IOANT on vertical and torsional deviation, as well as on IOOA. It builds upon the findings from our initial 21 IOANT cases presented at the 2021 ESA meeting.

Methods

Records of patients who underwent surgery with IOanterior and nasal transposition at the Department of Ophthalmology, Rigshospitalet - Glostrup, Copenhagen University Hospital, , from January 1, 2018, to December 31, 2023, were reviewed. The primary endpoints were changes in vertical deviation measured in prism diopters (PD), alterations in IOoveraction (IOOA) graded from 0 to 4, and variations in cyclotropia measured in degrees. Surgeries of transitioning from IO transposition (IOt) to IOANT were analyzed separately.

Results

IOANT was performed in 86 patients and reduced median vertical deviation from 22 PD to 1 PD with a mean effect of 21PD (range 0-48PD). Median IOOA decreased from 3 to 0.5 with a median effect of 2.6 (interquartile range [2;3]). Excyclotropia was reduced with a mean of 7 degrees (range -2-16).  In 6 patients we performed a transitioning procedure from inferior oblique transposition (IOt) to IOANT, and median vertical deviation decreased from 10 PD to -1 PD with a mean effect of 10PD (range 2-17PD), and median IOOA decreased from 1 to 0 with a median effect of 1.

Discussion

IOANT is an effective, single-muscle procedure for addressing fourth nerve palsy characterized by substantial vertical deviations, excyclotropia, and significant IOOA. Additionally, the conversion from IOt to IOANT is a valuable procedure in instances of undercorrection following the initial surgery.

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