Comparative Study Of The Effect Of Inferior Oblique Muscle Weakening Procedure On Surgical Alignment Of Children With Conmittent Exotropia

[Background] The inferior oblique muscle weakening procedure is the common surgical procedure of superior oblique palsy, inferior oblique hyperfunction, V-type exotropiaand double transfer of muscle paralysis and other diseases.The main purposes of inferior oblique muscle weakening procedure is to eliminate the vertical deviation and eye movement disorders in order to improve fusion function and binocular vision. The function of the inferior oblique muscle is mainly extorsion and elevation of the eye, additionally it is acts as adductor, but in or near its primary position the horizontal action of the inferior oblique muscle is slight. The experience is that the inferior oblique muscle weakening procedure has, besides a vertical effect, occasionally there is also an effect on the horizontal angle, which is always to be taken into consideration by the surgeon when planning to operate on the inferior oblique muscle. However, there are very few references to the effect of this operation on the horizontal angle, several authors state that the weakening procedure on the inferior obliques effects a5PDto10PDpermanent esophoria shift in the alignment of the eyes while others suggest that in the majority of patients the inferior oblique muscle weakening procedure had very little or no effect on the horizontal angle. The fear of converting a small esophoria into a larger esotropia by the weakening procedure on the inferior obliques either could deter the surgeon from doing the inferior oblique surgery or prompt them to offset the presumed postoperative esophoria shift by combining some appropriate horizontal muscle correction with the inferior oblique weakening surgery. This study was to determine the answer to this prevalent clinical worry.[Object] The object of the present study was undertaken to investigate the effect of inferior oblique muscle weakening procedure on mainly the horizontal deviation after horizontal recti recession-resection or recession procedure for children with exotropia.[Methods] In a retrospective, consecutive and interventional case series,179(male105,female72) patients underwent horizontal recti recession-resection or recession procedure for exotropia(15～55PD),respectively, from August2009to September2011at Shandong Provincial Hospital. All the patients met the following inclusion criteria:(1) exotropia measuring15～55PD with optical correction;(2) age from3-15years old(7.02±0.20);(3) no anisometropia;(4) full preoperative ductions and full versions,no diplopia;(5) no amblyopia;(6) no history of strabismus surgery;(7) All surgeries were performed by one of the authors(LW) together with a resident assistant;(8) the amount of horizontal muscle correction was correlated specifically with the amount of exotropia and (9)postoperative follow-up for at least6months(8.88±0.36). Each patient underwent detailed enquiry with regard to the disease history and routine ophthalmological and orthoptic examination before the operation, including anterior segment assessment, fundus examination,best corrected visual acuity measurement, cycloplegic refraction measurement and motility evaluation. Alternate prisms cover test was used to measure the horizontal deviation before and after surgery by the operating surgeon.Deviations were measured at both medium distance (6m) in primary and lateral gaze and near distance (1/3m) in primary gaze while viewing accommodative targets with full cycloplegic refraction correction. The Krimsky light reflex test was used for very young children,but only in primary gaze.48of the179patients who underwent horizontal recti recession-resection or recession procedure and inferior oblique muscle weakening procedure were in the group A and131who was only treated with inferior oblique muscle weakening procedure were in the group B. A successful alignment was defined as0-±8PD in primary gaze while fixing distant and near accommodative targets.The postoperative examination was carried out at postoperative days1-3and a minimum of6months final follow-up.[Results] Between A and B group the successful rate in alignment at postoperative day1～3were72.9%,72.5%(χ2=0.03, P=0.958), and the overcorrection rate were 22.9%,21.4%(χ2=0.049, P=0.825),and the undercorrection rate were4.2%,6.1%(χ2=0.018, P=0.894). Between A and B group the successful rate in alignment at final follow-up were62.4%,69.4%(χ2=0.778, P=0.378), and the overcorrection rate were6.3%,4.6%(χ2=0.004, P=0.947),and the undercorrection rate were31.3%,26.0%(χ2=0.496, P=0.481)[Conclusions] The horizontal effects of inferior oblique muscle weakening procedure can be performed without disadvantage on patients who underwent recti recession-resection or recession procedure for exotropia. Eye surgeons do not need to change the conventional amounts of eye muscle surgery for horizontal binocular deviations when oblique muscle weakening procedures are simultaneously performed.