Oscillopsia and the influence of stress and motivation in fusion maldevelopment nystagmus syndrome.

PURPOSE

We examined factors influencing perceptual stability in observers with fusion maldevelopment nystagmus syndrome (FMNS). In addition, we also investigated the effect of visual demand, task-related physiologic stress, and motivation on the nystagmus waveform.

METHODS

Perception of oscillopsia during daily activities was assessed via a questionnaire. Perception of oscillopsia in the laboratory was assessed using central and peripheral (10°) light emitting diodes (LEDs) in front of a background display of random, fixed-contrast shapes. Task-induced stress was achieved via a time restricted acuity task with or without concurrent mental arithmetic challenge, and motivation varied using a reward-penalty paradigm. The experiments have been previously described elsewhere.

RESULTS

Six out of nine subjects reported experiencing oscillopsia in certain daily activities. in the laboratory, the percentages of trials with perceptions of motion of the led and background were as follows: neither, 60% to 70%; background only, 20% to 30%; both, 5% to 15%, and LED only, 5% to 15%. Over all trials, six of nine experienced oscillopsia for both the low- and high-contrast image respectively (i.e., three subjects never experienced oscillopsia). The background was frequently seen moving for both images regardless of contrast and/or condition. Trials with and without oscillopsia did not differ when comparing foveation. In the second experiment, task-related physiologic stress and motivation were reflected in an increase in heart rate; nystagmus waveform intensity increased and foveation decreased. The magnitude of changes in heart rate was uncorrelated with changes in waveform parameters for all experiments, however.

CONCLUSIONS

Preliminary results suggest that the FMNS group does perceive spatially inhomogeneous oscillopsia, similar to infantile nystagmus syndrome (INS), in certain visual environments. In investigating the effect of stress and motivation on FMNS, a new, if tentative, finding suggests that task-induced stress and/or motivation may have a negative impact on the nystagmus. Taken together, our findings provide an insight into the particular environments and tasks that are likely to present particular challenges to persons with FMNS.