Purpose It is generally agreed that vertical prism bar training can increase vertical fusion amplitude. However, little is known as to whether the increased vertical fusion amplitude following vergence exercise is due to improvement of the sensory or the motor system or both. The main aim of the present study was to determine the effect of vertical prism bar training on the motor and sensory components of vertical fusion. Methods Fifty normal subjects between 17 and 25 years of age were given vertical prism bar training to improve their vertical fusion amplitude. Vertical vergence eye movements were recorded using an infrared reflectance eye tracker system. The sensory component was assessed using a Sheedy disparometer. Results The findings of the present study showed that the average increase in vertical motor fusion was approximately 30% following vertical prism bar training. The maximum magnitude of VFD remained unchanged in the majority (73%) of subjects. Conclusions The increase in the vertical fusion amplitude following vertical prism bar training is largely due to improvements in the vertical motor fusion. The prism training has little effect on the sensory component.