Abstract
Purpose::
To investigate quantitatively the effects of stress and arousal on infantile nystagmus syndrome (INS). It is widely reported that psychological factors including fatigue, stress and attention have profound effects on the nystagmus waveform, which have implications for visual function. However, despite stress being a frequent condition experienced by people with INS in everyday life, such effects have never been quantified.
Methods::
The eye movement behaviors of 9 subjects with INS were recorded at the null zone, using the Skalar IRIS system, while viewing a stationary black spot subtending 0.2º at 7m. The sound of crashing waves (as a relaxant) was played to the subjects through headphones during this time. After 2 minutes, subjects completed a visual acuity (VA) task using Landolt C targets and a two-alternative forced choice staircase procedure. On reaching their visual acuity threshold, an 88dB siren (stressor) was played through the headphones while the subject continued with the task. After 1 minute, the siren was terminated and crashing waves were played for a further minute. Skin conductance (SC) was recorded throughout as a measure of arousal. Data were analyzed for changes in the eye movement characteristics under the situations of no stress (crashing waves) and stress (siren). VA data were analyzed for a change in threshold during the stressor.
Results::
All 9 subjects showed a significant increase in SC at the onset of the siren. Analyses of combined data revealed a significant increase in nystagmus intensity (p<0.05) after the onset of the siren. The impact of the siren on VA was subject dependent, VA was more affected in those who displayed a marked increase in intensity.
Conclusions::
The stressor used in this study produced an increase in nystagmus intensity, suggesting that the manipulation of a subject’s state of arousal can influence the generation of eye movements, presumably mediated by the reticular formation. The effect of such a stressor both to the nystagmus waveform and VA appears to vary with the subject. The subject most affected by the stressor displayed a 0.1logMAR drop in acuity, which would noticeably affect performance on certain visual tasks. Our results indicate that stress can have a deleterious impact on VA in those with INS.
Keywords: nystagmus • visual acuity • eye movements