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H.E. Bedell, M. Ramamurthy, S.S. Patel; The Temporal Impulse Response Function in Infantile Nystagmus . Invest. Ophthalmol. Vis. Sci. 2003;44(13):2739.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Despite rapid to-and-fro motion of the retinal image that results from their involuntary eye movements, persons with infantile nystagmus (IN) rarely report the perception of motion smear. We asked if the reduction of perceived motion smear is attributable to an increase in the speed of the temporal impulse response in persons with IN. Methods: Increment thresholds were determined for pairs of successively presented flashes (5.9 ms each) of a long horizontal line, presented on a 65 cd/sq m background field, 1 deg above or below a continuously visible cross. The stimulus-onset asynchrony (SOA) between the first and second flash varied randomly among blocks of trials from 5.9 to 234 ms. Increment thresholds were measured as a function of SOA for 2 subjects with predominantly pendular IN and for 6 normal observers. Horizontal eye position was monitored in the subjects with IN in order to reject trials on which a nystagmus fast phase occurred during the presentation of the target lines. Temporal impulse response functions were modeled as impulse responses of a second order linear system and were estimated using an optimization procedure in Matlab. Each estimated impulse response function provided the best fit to the increment threshold data when summed at the various SOAs. Results: Measured 2-pulse increment thresholds changed relatively similarly with SOA in the subjects with IN and the normal observers. However, the estimated temporal impulse response functions indicated natural temporal frequencies of approximately 14 Hz in the subjects with IN, compared to a median value of approximately 10 Hz in the normal observers. Conclusions: Although the fitted temporal impulse response functions indicate a faster-than-normal temporal response in subjects with IN, the increase in response speed is too small to account for the virtual absence of perceived motion smear.
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