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P. H. Jones, J. M. Woodhouse, T. H. Margrain, F. Ennis, C. M. Harris, J. T. Erichsen; The Effects of Stress on INS. Invest. Ophthalmol. Vis. Sci. 2010;51(13):5480. doi: https://doi.org/.
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Most of the evidence currently available regarding the effects of stress on nystagmus is anecdotal. However, recent research has reported that visual acuity (VA) is not significantly affected by stress. The purpose of this study was to investigate what leads to the perception that stress causes a worsening of "vision" in people with nystagmus.
VA was measured at distance using a two alternative forced choice (2AFC) staircase method. Subjects were asked to identify the gap in a Landolt C of decreasing size as being to either the left or the right. Eye movements were simultaneously recorded. Skin conductance was also recorded. An increase in skin conductance has been shown to be directly linked to an increase in a person’s level of arousal. Stress was induced with the threat of a brief shock from a Transcutaneous Electric Nerve Stimulation (TENS) machine at double the subject’s threshold (threshold measured prior to the start of the investigation), although this was never actually done. Subjects carried out the visual task four times, twice under relaxed conditions, and twice under stressed conditions (one with shock linked to performance and the other with shock at random intervals).
The data showed that the intensity of eye movements was significantly increased during periods of stress (paired sample t test, p< 0.05) as was skin conductance (p< 0.05). Consistent with other studies, VA was not significantly different (p=0.73). However, the time taken for subjects to respond to the stimulus was found to be significantly longer during periods of stress (p< 0.05).
The experimental results suggest that there are aspects of "vision" other than VA that can better reflect the problems experienced by people with nystagmus when they are placed under stress. We can show that, although VA is unaffected, subjects take longer to identify the target. We conclude that clinical or experimental measures of VA alone are insufficient to determine the visual problems faced by people with nystagmus. The inclusion of additional tests such as measurement of the time taken to correctly identify a target would provide greater understanding.
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