Does fixation light intensity influence the results from the Sbisa bar when measuring sensory fusion?

Aim: To determine whether the level of sensory fusion in normal participants is affected significantly by fixation light intensity. Methods: Seventeen normal adult participants had sensory fusion measurements taken using the Sbisa bar, combined with Bagolini glasses, as a control for binocular single vision, whilst fixating lights of three different intensities: 150 lux, 250 lux and 350 lux. Data were analysed using Friedman’s test and the Wilcoxon matched pairs signed ranks test. Results: Seventeen participants were tested (mean 35.3 years, range 23–60 years). Friedman’s test showed at least two of the light intensities had a statistically significant effect upon sensory fusion results ( p = 0.011). Wilcoxon matched pairs signed rank testing found no statistically significant difference in levels of sensory fusion when fixating the 150 lux and 250 lux fixation lights ( p = 0.194). There was a statistically significant difference in the level of sensory fusion when fixating the 150 lux and 350 lux lights ( p = 0.011) and the 250 lux and 350 lux lights ( p = 0.017). Conclusion: Changing the intensity of the fixation light from 150 lux to 350 lux and from 250 lux to 350 lux significantly affected the level of sensory fusion measured. The higher the intensity of the light, the greater the filter needed to break fusion. The clinical significance of these results is considered.