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Influence of motion smear on visual acuity in simulated infantile nystagmus
Susana T L Chung1, Martin W LaFrance, Harold E Bedell
1School of Optometry, University of California, Berkeley, Berkeley, California, USA.
Insights
Visual acuity in normal observers is impaired by the rapid image motion during the non-foveating phases of infantile nystagmus (IN). This effect is more pronounced with increased stimulus presentation cycles, suggesting motion smear significantly impacts vision.
Area of Science:
- Ophthalmology
- Neuroscience
- Visual Science
Background:
- Infantile nystagmus (IN) is an involuntary eye movement condition.
- Visual acuity in IN is typically linked to the foveation period, where retinal image velocity is low.
- The impact of the high-velocity, non-foveating phases of IN on visual acuity is not fully understood.
Purpose of the Study:
- To investigate how the non-foveating phases of the infantile nystagmus waveform affect visual acuity in normal observers.
- To compare visual acuity when viewing stimuli during simulated whole IN waveforms versus simulated foveation periods only.
Main Methods:
- Visual acuity was measured in three normal observers using T-stimuli.
- Stimuli were presented during simulated infantile nystagmus (IN) waveforms, including whole-waveform and foveation-only conditions.
- Simulated foveation durations varied from 20 to 120 ms, and stimulus presentation across multiple cycles was examined.
Main Results:
- Visual acuity improved with longer simulated foveation durations in both conditions.
- Visual acuity was consistently better in the foveation-only condition compared to the whole-waveform condition.
- The detrimental effect of high-velocity motion was more apparent with multiple stimulus cycles due to summation in the foveation-only condition.
Conclusions:
- In normal observers, visual acuity is degraded by both the foveation duration and the high-velocity motion during the non-foveating phases of IN.
- The findings suggest that rapid retinal image motion during IN's non-foveating phases negatively impacts visual acuity.
- Further research is needed to determine if this degradation occurs similarly in individuals with IN, who report minimal motion smear.
Purpose:
In persons with infantile nystagmus (IN), visual acuity correlates with the duration of the foveation period of the nystagmus waveform, i.e., when the retinal image is on or near the fovea and moves with low velocity. In this study, we asked how acuity is affected by the non-foveating phases of the nystagmus waveform, when the velocity of retinal image motion is substantially higher.
Methods:
Visual acuity was measured in three normal observers for high contrast, four-orientation single T-stimuli, presented during image motion that simulated either the whole jerk-IN waveform (whole-waveform) or only the foveation periods of the IN waveform (foveation-only). Simulated foveation durations ranged from 20 to 120 ms. For both motion waveforms, we displayed the acuity target for different number of cycles to examine whether acuity benefits from multiple presentations of the stimulus.
Results:
As expected, visual acuity improves with longer simulated foveation durations in both the whole-waveform and foveation-only conditions. Acuity is consistently better (by ∼0.1 logarithm of the minimum angle of resolution) in the foveation-only than the whole-waveform condition, indicating that the high-velocity image motion during the simulated IN waveform has a detrimental effect. This difference in acuity between the two waveform conditions increases with the number of cycles, apparently because summation occurs across cycles in the foveation-only condition but not in the whole-waveform condition.
Conclusions:
In normal observers, visual acuity in the presence of a simulated nystagmus waveform is limited not only by the duration of the foveation periods, but also by the non-foveating phases of the waveform. However, because persons with IN report little or no motion smear in association with their nystagmus, it remains unclear whether the rapid retinal image motion during the non-foveating phases of the nystagmus waveform generates a similar degradation of visual acuity in IN.
