Computer vision syndrome (CVS) is a complex of symptoms experienced by up to 90% of computer users. Questions remain regarding its etiology. Changes in accommodation or vergence have been suggested as causative factors. This study sought to determine if subjects with CVS had abnormal accommodative or vergence facility findings and to identify if sustained computer use produces a change in these parameters. Twenty two subjects read text from a computer screen for a continuous 25 min period. Vergence facility and both monocular and binocular accommodative facility were measured. Following the computer task, subjects completed a questionnaire regarding their level of discomfort during the task. No significant change in monocular accommodative or vergence facility was observed following the computer task, although a small increase in post-task binocular accommodative facility was noted. The highest ocular symptoms reported were tired eyes, eyestrain and dry eye. These were not correlated significantly with the accommodative or vergence facility findings.The symptoms reported appeared to be related to dry eye, and not to either accommodative or vergence abnormalities.
Previous studies have found the modified Thorington test and the Howell phoria card test to be more repeatable than the von Graefe test. Another potential way to assess the value of a test could be to
correlate test results with the level of symptoms. Near dissociated phorias were measured with the modified Thorington, Howell phoria card, and von Graefe procedures with 50 subjects between the ages
of 18 and 35. The von Graefe test was performed with two different targets, thus making a total of four different phoria tests. All testing was performed using a phoropter. Test findings were correlated
with symptom scores from a questionnaire. The means on the four tests ranged from 2.7Δexo to 3.7Δ exo. Correlations of phoria findings with symptom scores were not statistically significant for any of the
four tests in subjects with exophoria. In a small number of subjects with esophoria, significant correlations were found between phoria and symptom scores for the modified Thorington test and the
Howell phoria card test but not with the von Graefe test. The modified Thorington test and the Howell phoria card test were more repeatable than the von Graefe test
The purpose of this experiment was to study the role of binocular vision, including both stereopsis and binocular vergence, on the complex task of golf putting. The putting accuracy of 16, visually-normal, inexperienced golfers (range 23-66 years, mean=35 years) was assessed for small (3cm) and large (12cm) targets located at 3, 6, and 9 feet with their distance corrective lenses in place. Subjects performed the task under either normal binocular or monocular viewing conditions. Putting accuracy (% successful putts) was significantly better under binocular versus monocular viewing conditions for the smaller target. This was true for 10 out of 12 (83%, p=0.019), 11 out of 12 (92%, p=0.003), and 12 out of 12 (100%, p<0.001) of the subjects for the 3-, 6-, and 9-foot test distances, respectively. The percentage improvement in putting accuracy under binocular as compared to monocular viewing conditions for the small (3cm) target was 14%, 8%, and 13% for the 3-, 6-, and 9-foot target distances, respectively. For the larger target, the trends were similar but smaller in magnitude (0.5-7%) and not statistically significant. These findings are consistent with earlier studies demonstrating improved athletic performance under binocular versus monocular viewing conditions. The additional depth-related cues provided by stereopsis and binocular vergence appear to be crucial for more precise and detailed tasks, such as were present with the smaller target.
Many experiments conducted by behavioral scientists involve brief presentation of visual stimuli. These experiments frequently utilize subjects with only self-reported normal vision. It has been observed, however, that at least some of these subjects possess visual deficits that affect the processing of visual stimuli under normal viewing conditions. Experiment 1 examined whether participants with only self-reported normal vision process briefly presented visual stimuli as accurately as those with verified normal vision. Results indicate that a group with only self-reported normal vision actually possess a number of deficits at both near- and farpoint. Further, this group processed briefly presented visual stimuli significantly less effectively as compared to a group with verified normal vision. The most prevalent visual deficits observed in experiment 1 were nearpoint binocular deficits as determined by the Keystone Visual Skills Series. Experiment 2 therefore, examined the effects of specific nearpoint binocular deficits on brief stimulus processing. Results indicate that both underconvergence and overconvergence binocular deficits at near point have a significant negative effect on the processing of briefly presented visual stimuli. Overall results are discussed in terms of reducing extraneous variance factors by carefully assessing vision capabilities, particularly nearpoint binocular deficits, in experiments utilizing briefly presented visual stimuli. Implications of the findings for optometric researchers and clinicians are discussed.
Vergence refers to the disjunctive movement of the eyes used to track targets moving in depth. In this invited paper, the sensory, motor, and perceptual aspects of clinical near vergence testing are described and discussed in detail, with introduction of concepts developed in bioengineering. In addition, new tests are described and suggested for use by the functional optometrist.
Research has shown a relationship between improvements in accommodative functioning and certain visual perceptual skills. One explanation for these results is that accommodative dysfunction interferes with the development of visual attention. This study compared three components of attentional ability: coming to attention, decision making, and sustaining attention by children with and without non-strabismic dysfunctions of accommodation and/or vergence. Twenty children, ages 8 to 11 years (10 boys and 10 girls) of normal intelligence participated in this study. The group with inefficient visual skills performed significantly poorer compared to the visually normal functioning group on coming to attention and sustaining attention but not on decision making. This implies that a relationship exists between dysfunctions in accommodation and/or vergence and dysfunctions of certain attentional skills.
Behavioral optometry is rooted in the system of numbers known as the 21-point visual analysis. Through the years additional performance tests and clinical insight have tempered the reliance upon mathematical formulation of case typings. The complexity and dynamic nature of the visual process necessitates new paradigms to objectively arrive at acceptable levels of performance. The new science of chaos holds promise in this regard, providing mathematical profiles of complex and dynamic human systems. Through study of the non-linear nature of the cardiac system, scientists are beginning to appreciate the purposeful chaos of the heart, wherein absolute equilibrium is undesirable. This paper explores the possibilities for application of chaos theory to the non-linear nature of the visual system.