Abstract
In reading, binocular eye movements are required for optimal visual processing and thus, in case of asthenopia or reading problems, standard orthoptic and optometric routines check individual binocular vision by a variety of tests. The present study therefore examines the predictive value of such standard measures of heterophoria, accommodative and vergence facility, AC/A-ratio, NPC and symptoms for binocular coordination parameters during read-ing. Binocular eye movements were recorded (EyeLink II) for 65 volunteers during a typical reading task and linear regression analyses related all parameters of binocular coordination to all above-mentioned optometric measures: while saccade disconjugacy was weakly pre-dicted by vergence facility (15% explained variance), vergence facility, AC/A and symp-toms scores predicted vergence drift (31%). Heterophoria, vergence facility and NPC ex-plained 31% of fixation disparity and first fixation duration showed minor relations to symp-toms (18%). In sum, we found only weak to moderate relationships, with expected, selective associations: dynamic parameter related to optometric tests addressing vergence dynamics, whereas the static parameter (fixation disparity) related mainly to heterophoria. Most sur-prisingly, symptoms were only loosely related to vergence drift and fixation duration, re-flecting associations to a dynamic aspect of binocular eye movements in reading and poten-tially non-specific, overall but slight reading deficiency. Thus, the efficiency of optometric tests to predict binocular coordination during reading was low – questioning a simple, straightforward extrapolation of such test results to an overlearned, complex task.
Highlights
Up-to-date, we know exactly, how the horizontal binocular coordination during reading typically works: the movements of the left and right eye during each saccade are not identical, leading to a disconjugacy during the saccade (Collewijn, 2001; Heller & Radach, 1999)
We replicated the stereotyped pattern of binocular eye movements during reading: disconjugacies during saccades are followed by a drift during fixations and small vergence errors remained at the end of fixations (Heller & Radach, 1999; Howard, 2012), while reading times, numbers of saccades and saccade amplitudes, all resembled a typical eye movement behavior during reading (Liversedge, White, et al, 2006; Nuthmann & Kliegl, 2009)
We found a typical range of binocular vision qualities in our participant sample, showing heterophorias between 6 and 8 degrees, vergence facilities between 6 and 18 cpm, binocular accommodative facilities ranging from 1 to 17 cpm, near point of convergence amounting to 6.1 cm, on average, and asthenopic symptoms ranging up to 32 points of Convergence Insufficiency Symptom Survey (CISS) score
Summary
Up-to-date, we know exactly, how the horizontal binocular coordination during reading typically works: the movements of the left and right eye during each saccade are not identical, leading to a disconjugacy during the saccade (Collewijn, 2001; Heller & Radach, 1999). A horizontal fixation disparity reflects, that the visual axes of the eyes cross slightly in front (eso) or behind (exo) the plane of fixation (Howard, 2012; Jaschinski, 2017; Steinman, Steinman, & Garzia, 2000) This small vergence error typically amounts to about one character size, that is, 0.2 to 0.5 degrees This small vergence error typically amounts to about one character size, that is, 0.2 to 0.5 degrees (Kirkby, Blythe, Drieghe, Benson, & Liversedge, 2013; Liversedge, Joss, J. & Jainta, S. (2021) Optometric tests and binocular reading
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