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The aim of this work was to find out if differences exist in accommodative and convergence response for different
computer monitors' and a printed text. It was also tried to relate the horizontal heterophoria value and accommodative
response with the symptoms associated with computer use.
Two independents experiments were carried out in this study. The first experiment was measuring the accommodative
response on 89 subjects using the Grand Seiko WAM-5500 (Grand Seiko Co., Ltd., Japan). The accommodative
response was measured using three computer monitors: a 17-inch cathode ray tube (CRT), two liquid crystal displays
LCDs, one 17-inch (LCD17) and one 15 inches (LCD15) and a printed text. The text displayed was always the same for
all the subjects and tests. A second experiment aimed to measure the value of habitual horizontal heterophoria on 80
subjects using the Von Graefe technique. The measurements were obtained using the same target presented on two
different computer monitors, one 19-inch cathode ray tube (CRT) and other 19 inches liquid crystal displays (LCD) and
printed on paper. A small survey about the incidence and prevalence of symptoms was performed similarly in both
experiments.
In the first experiment, the accommodation response was higher in the CRT and LCD's than for paper. There were not
found significantly different response for both LCD monitors'. The second experiment showed that, the heterophoria
values were similar for all the stimuli. On average, participants presented a small exophoria. In both experiments,
asthenopia was the symptom that presented higher incidence.
There are different accommodative responses when reading on paper or on computer monitors. This difference is more
significant for CRT monitors. On the other hand, there was no difference in the values of convergence for the computer
monitors' and paper. The symptoms associated with the use of computers are not related with the increase in
accommodation and with the horizontal heterophoria values.
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