Functional changes of visual cortex in pre- and post- operative intermittent exotropia patients: study protocol for a non-randomized case-control clinical trial

Abstract

AbstractIntroductionIntermittent exotropia (IXT) is the most common type of divergent squint. IXT is primarily a cortical neurologic dysfunction disorder, occurring as a result of insufficient maintaining of sensory and motor fusion. Recent reports have demonstrated the relationship between IXT and visual cortical impairment. We plan to assess blood oxygen level-dependent (BOLD)- functional magnetic resonance imaging (fMRI) in IXT patients during the pre-and post-operation follow-ups to evaluate the functional changes of the visual cortex.Methods and analysisA total of 90 Chinese subjects will be recruited, and the age is between 18 and 60 years old. The subjects include the Surgical treatment (ST) group (45 IXT subjects who will perform surgery) and the Healthy control (HC) group (45 age - and sex - and education matched healthy volunteers). The assessments include the following aspects: general ophthalmic, optometry, binocular vision test, Newcastle Control Score (NCS), and fMRI. Each subject completes the rest-state BOLD-fMRI, and the sequences include echo planar imaging (EPI) pulse and 3-dimensional brain volume (3D-BRAVO) to acquire high-resolution images. The follow-up schedule is 6 and 12months after the surgery. The primary outcome will be determined by cortex changes in BOLD-fMRI in ST group before and after the surgery. We also compare the HC group with the pre-operation subjects in the ST group. The secondary outcomes are changes of strabismus examinations, binocular visual function examinations, and NCS.Ethics and disseminationEthical approval has been obtained from the Medical Ethics Committee of the Beijing Tongren Hospital. We plan to publish the results of this study in a peer-reviewed journal article.Trial registration numberChiCTR2100048852Strengths and limitations of this studyThe present study is advanced which aims to explore the functional changes in the visual cortex in IXT patients before and after surgery through rest-state 3.0T BOLD-fMRI. We also explore the relationships between changes of cortex and ocular examination.The follow-up comparison between the visual cortex and ophthalmic changes will enrich our understanding of the impairment and plasticity of visual function in IXT patients.Loss to follow-up of participants is possible after the surgery in this study.The present study focuses on IXT patients with surgical indications. We did not carry on the study on the different subtypes or the different severity of IXT.