NCT03459092.

Study name	Botox Instead of Strabismus Surgery (BISS)
Methods	Randomized, parallel‐group, controlled trial
Participants	Inclusion Criteria Informed consent of trial participant and/or legal representative documented per signature Age > 1 year and < 17 years Esotropia > 10 Prisms Indication for an intervention (either Botox or surgery) has been made. Any of the following Presence of a secondary strabismus from binocular disruption the cause of the binocular disruption is no longer present Decompensated microstrabismus Decompensated phoria Acute acquired esotropia Positive test of binocular function at any time point in the past, including any of the following Titmus test Bagolini striated glasses test Lang‐stereo‐test with correct naming of at least one panel Good ocular alignment after 6 months of age on at least 2 photographs Exclusion Criteria Known hypersensitivity to botulinum toxin Known neuromuscular disorder Known present neurological disorder affecting the central nervous system Including paresis on cranial nerves number 3, 4 and 6 Any of the following nystagmus dissociated vertical deviation Vertical deviation in any gaze direction greater than 5° Incomitance with more than 5° of difference between the left and right horizontal gaze direction Previous strabismus surgery Previous botulinum toxin treatment on extraocular muscles Presence of ophthalmic pathologies significantly preventing binocular functions. A significant alteration of binocular function is assumed if vision is smaller than 0.1 or the visual field has a horizontal diameter of less than 20°. Pregnancy. A negative pregnancy test before randomization is required for all women of child‐bearing potential. Preterm children born before 36 weeks of gestation.
Interventions	Intervention 1: botulinum toxin type A Intervention 2: strabismus surgery
Outcomes	Primary outcome Number of participants with presence of binocular vision Secondary outcomes Number of participants with second intervention Number of participants with binocular vision Number of participants with incomitance Number of participants with treatment‐specific presence of binocular vision Number of surgeries per participant Number of surgeries needed per successful outcome Change in strabismus angle, measured in per cent Binocular function, measured in arc seconds Other Outcome Measures Total duration of binocular vision (exploratory outcome) Incidence of short‐term adverse events (safety outcome) Incidence of ocular adverse events Incidence of serious adverse events related to the treatment
Starting date	16 August 2018; estimated completion August 2023
Contact information	Principal Investigator: Professor Mathias Abegg, Bern University Hospital
Notes