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INTRODUCTION Binocular vision requires that the vergence angle between the two visual axes be adjusted for proper fusion of the two retinal images so that the point of regard is […], Some observers do not fixate accurately at the point of regard: Their vergence angle (between the visual axes of the two eyes) may correspond to points slightly nearer or farther away. This vergence error, or fixation disparity, was measured with nonius (vernier) lines at six positions of a visual display relative to the eyes. At viewing distances of 40, 60, and 100 cm, the display was located either at eye level or at a downward inclination of gaze direction of -25° relative to horizontal. Viewing conditions resembled typical office work. Lowering the screen induced a near shift in mean vergence response of 0.6 mm arc, irrespective of viewing distance; the closer the screen, the more distant was the vergence response relative to the target (by 2.5 mm arc on average). The slope of this proximity-fixation-disparity curve is an individual parameter of the vergence system. Actual or potential applications of this research include recommendations for the comfortable viewing distance of visual displays.

Efforts made to examine whether saccadic eye movements across computer screens may be effected by the intermittency of light of cathode ray tubes (CRT) is presented. The results suggested that the intermittent light of cathode ray tube screens does not prolong the latency of saccades.

Northwestern Switzerland, Institute of Optometry Reading with two eyes necessitates efficient processes of binocular vision, which provide a single percept of the text. These processes come with a binocular advantage: binocular reading shows shorter average fixation durations and sentence reading times when compared to monocular reading. In Jainta and Jaschinski (IOVS; 2012; N = 13), we showed that binocular advantages critically relate to the individual heterophoria (the resting state of vergence) and in the present, large-scale replication we set out to quantify heterophoria impacts on binocular advantages in reading. We collected binocular eye movements (Eyelink II) for 94 participants who read 20 sentences monocularly and 20 sentences binocularly. Further, individual heterophorias were determined using three different, optometric standards: objective eye tracking (EyeLink II at 60 cm), Maddox wing test (at 30 cm) and MKH measures (at 5.5 m). Binocular eye movements showed typical pattern in monocular reading (larger saccades and changed binocular coordination) and impacts of increased heterophoria on binocular coordination in binocular reading. More importantly, we replicated (1) binocular advantages of about 25 ms for average fixation durations and (2) a reduction in binocular advantages when heterophoria increased. The latter was true only when heterophoria was identified by EyeLink II or Maddox wing measures (MKH measures of heterophoria did not affect binocular advantages in reading). In detail, for large heterophorias (3 degrees and larger) binocular reading even turned into a disadvantage. Implications for effect estimations through LME modelling and optometric treatments based on different heterophoria measures will be discussed. [ABSTRACT FROM AUTHOR]

We investigated the way in which binocular coordination in reading is affected by the spatial structure of text. Vergence eye movements were measured (EyeLink II) in 32 observers while they read 120 single German sentences (Potsdam Sentence Corpus) silently for comprehension. The similarity in shape between the neighboring strokes of component letters, as measured by the first peak in the horizontal auto-correlation of the images of the words, was found to be associated with (i) a smaller minimum fixation disparity (i.e. vergence error) during fixation; (ii) a longer time to reach this minimum disparity and (iii) a longer overall fixation duration. The results were obtained only for binocular reading: no effects of auto-correlation could be observed for monocular reading. The findings help to explain the longer reading times reported for words and fonts with high auto-correlation and may also begin to provide a causal link between poor binocular control and reading difficulties.