The effect of different types of convergent strabismus on horizontal eye movements

Purpose To investigate the effect of different types of convergent strabismus on horizontal eye movements and compare data with healthy control subjects. Materials and methods This prospective, cross-sectional study included 38 patients with convergent strabismus (16 fully accommodative, 13 partially accommodative and 9 non-accommodative esotropia) and 19 age-matched control subjects. All of the participants had a detailed ophthalmological examination including visual acuity assessment, cover-uncover prism test, slit lamp, and indirect ophthalmoscopy examination. Videonystagmography (VNG) was used for the evaluation of horizontal eye movements such as saccadic accuracy, velocity, latency, and smooth pursuit velocity gain. Results The saccadic accuracy in the rightward direction was lower in the fully accommodative esotropia group compared to the partially accommodative esotropia group in the right eye ( p = 0.002 ). The saccadic latency in the rightward direction was longer in the fully accommodative esotropia group compared to the control group ( p = 0.008 ) and smooth pursuit velocity gain in the leftward direction was lower in the partially and non-accommodative esotropia group compared to the control group in binocular recording ( p = 0.004, p = 0.001, respectively). There was no difference in the saccadic velocity among the study groups ( p > 0.05 ). Finally, asymmetry of saccadic velocity and latency was observed between right- and leftward directions in the partially accommodative esotropia group in the right eye ( p = 0.003, p = 0.008 , respectively). Conclusion This study demonstrated that horizontal eye movements may vary in different types of convergent strabismus. VNG may be an auxiliary tool to the clinical examination in differentiating fully or non-accommodative esotropia.