Dynamics of accommodative fatigue in rhesus monkeys and humans

College of Optometry, University of Houston, 505 J Davis Armistead Bldg, 4901 Calhoun Rd, Houston, TX 77004, USA.
Vision Research (Impact Factor: 1.82). 02/2005; 45(2):181-91. DOI: 10.1016/j.visres.2004.07.036
Source: PubMed

ABSTRACT Changes in accommodative dynamics with repeated accommodation were studied in three anesthetized rhesus monkeys and two conscious humans. Maximum accommodation was centrally stimulated via the Edinger-Westphal nucleus in monkeys with a 4 s on, 4 s off paradigm (4 x 4) for 17 min, 4 x 1.5 for 27 min and 2 x 1 for 16 min. Humans accommodated repeatedly to visual targets (5 x 5; 5D and 2 x 2; 6D) for 30 min. In all cases, accommodation was sustained throughout. The anesthetized monkeys showed inter-individual variability in the extent of changes in accommodative dynamics over time while no systematic changes were detected in the human accommodative responses. Little accommodative fatigue was found compared to previous studies which have reported a complete loss of accommodation after 5 min of repeated stimulation in monkeys.

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    • "While skeletal muscle fatigue is defined as a progressive decline in maximum voluntary force produced by a muscle or a muscle group (Tanaka and Watanabe 2012), comparatively less is known about visual fatigue. It was recently suggested that the extraocular and ciliary muscles of the eye are, unlike skeletal muscles, resistant to fatigue (Prsa et al. 2010; Vilupuru et al. 2005). Hence, it is more likely that the trapezius muscle increases associated with the visually demanding tasks in this study were related to mental fatigue due to high visual attention, rather than eye muscle fatigue. "
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    ABSTRACT: To investigate if trapezius muscle activity increases over time during visually demanding near work. The vision task consisted of sustained focusing on a contrast-varying black and white Gabor grating. Sixty-six participants with a median age of 38 (range 19-47) fixated the grating from a distance of 65 cm (1.5 D) during four counterbalanced 7-min periods: binocularly through -3.5 D lenses, and monocularly through -3.5 D, 0 D and +3.5 D. Accommodation, heart rate variability and trapezius muscle activity were recorded in parallel. General estimating equation analyses showed that trapezius muscle activity increased significantly over time in all four lens conditions. A concurrent effect of accommodation response on trapezius muscle activity was observed with the minus lenses irrespective of whether incongruence between accommodation and convergence was present or not. Trapezius muscle activity increased significantly over time during the near work task. The increase in muscle activity over time may be caused by an increased need of mental effort and visual attention to maintain performance during the visual tasks to counteract mental fatigue.
    Arbeitsphysiologie 02/2015; 115(7). DOI:10.1007/s00421-015-3125-9 · 2.19 Impact Factor
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    • "results of Vilupuru et al . ( 2005 ) for the 5 and 6 D starting positions of disac - commodation . It is possible that neuro - muscular fatigue in the accommodative system and / or a generalized reduction in performance associated with visual fatigue ( Hasebe et al . , 2001 ; Owens & Wolf - Kelly , 1987 ; Takeda , Ostberg , Fukui , & Iida , 1988 ; Vilupuru et al . , 2005 ) could have masked the enhancement of peak velocity and peak acceleration of disaccommodation that was associated with the hyperopic shift in dark focus . The dynamics of accommodation step responses do not follow an ' initial - destination ' strategy ( Schor & Bharadwaj , 2006 ) and hence are unlikely to be aVected by changes in the l"
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    ABSTRACT: Peak velocity and peak acceleration of disaccommodation step responses remain invariant of response magnitude for a constant starting position and they increase linearly with proximity of starting position. This suggests that disaccommodation response is initiated towards an initial (default) destination and is switched mid-flight to attain the desired final destination. The dioptric location of initial destination was estimated from the x-intercept of regression of peak velocity on response starting position. The x-intercept correlated well with subject's cycloplegic refractive state and poorly with their dark focus of accommodation. Altering the dark focus by inducing fatigue in the accommodative system did not alter the x-intercept. These observations suggest that cycloplegic refractive state is a good behavioral correlate of initial destination of disaccommodation step responses.
    Vision Research 07/2006; 46(12):1959-72. DOI:10.1016/j.visres.2005.11.029 · 1.82 Impact Factor
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    ABSTRACT: The last fifty years of research on visual fatigue are surveyed, with special emphasis on results that may be important in the context of driving. Over that time, ideas about visual fatigue have varied, ranging from a broad application of the label eyestrain, to virtually any visual complaint (including poor acuity), to more specific applications of the term to mean visual discomfort associated with lengthy near-vision tasks. Much of the research reviewed concerns visual fatigue in the workplace, and places particular emphasis on extended use of video displays. One consequence of this emphasis on specific workplace circumstances is that substantial portions of the work on visual fatigue may not be fully applicable to driving. The mechanisms developed to explain workplace visual fatigue may not be strongly engaged in driving. This is especially likely for research that links visual fatigue to oculomotor changes in vergence and accommodation after near work. Visual fatigue in driving is likely to be more strongly related to mechanisms such as ocular surface irritation that may occur as a consequence of eyeblink suppression, or to declines in arousal level that may occur over the course of a lengthy drive. Research directions on possible links between visual fatigue and vehicle lighting are discussed, along with options for measurement. University of Michigan Industry Affiliation Program for Human Factors in Transportation Safety
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