How disruptive are monocular reading conditions really?

Abstract

Purpose. Based on the fact that reading with both eyes shows a binocular advantage of about 10 % (shorter reading and fixation times compared to monocular reading) with good binocular coordination, the present study aims to investigate the influence of the quality of binocular vision on the effectiveness of reading. Material and Methods. The binocular eye movements (Eyelink II) of 260 test subjects were reevaluated. All subjects read 60 sentences in German containing a target word occurring either frequently or rarely in this language. Additionally, the reading condition was changed from monocular to binocular for 30 sentences. Furthermore the objective heterophoria and MCH heterophoria for all participants were determined. Results. In the case of monocular reading conditions, there was only a weak general word-frequency effect (b = 7.21; t = 1.91; p = 0.06) but fixation times for frequent words shortened slightly when objective heterophoria increased (b = −4.24; t = −3.82; p < 0.001). For binocular reading conditions, on the other hand, there was a clear word-frequency effect (b = −48.77; t = −6.03; p < 0.001) and, at the same time, an interaction with individual heterophoria (objective: b = 8.19; t = 14.57; p < 0.001; MCH: b = 3.27; t = 4.40; p < 0.001). Conclusion. Monocular reading conditions can be proven to be disruptive when investigating people with good binocular coordination. However, this effect turns out to be much smaller than what is assumed by many optometrists. People with good binocular coordination clearly show greater benefits when reading with both eyes. Keywords: BINOCULAR COORDINATION, BINOCULAR ADVANTAGE, READING