Slow-phase onset influence on waveform identification and foveation time measure in congenital nystagmus

Giulio Pasquariello, Mario Cesarelli, Paolo Bifulco, Maria Romano, Antonio Fratini, Antonio La Gatta, Domenico Boccuzzi

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

Congenital nystagmus (CN) is an ocular-motor disorder characterised by involuntary, conjugated ocular oscillations and its pathogenesis is still under investigation. This kind of nystagmus is termed congenital (or infantile) since it could be present at birth or it can arise in the first months of life. Most of CN patients show a considerable decrease of their visual acuity: image fixation on the retina is disturbed by nystagmus continuous oscillations, mainly horizontal. However, the image of a given target can still be stable during short periods in which eye velocity slows down while the target image is placed onto the fovea (called foveation intervals). To quantify the extent of nystagmus, eye movement recording are routinely employed, allowing physicians to extract and analyse nystagmus main features such as waveform shape, amplitude and frequency. Using eye movement recording, it is also possible to compute estimated visual acuity predictors: analytical functions which estimates expected visual acuity using signal features such as foveation time and foveation position variability. Use of those functions extend the information from typical visual acuity measurement (e.g. Landolt C test) and could be a support for therapy planning or monitoring. This study focuses on detection of CN patients' waveform type and on foveation time measure. Specifically, it proposes a robust method to recognize cycles corresponding to the specific CN waveform in the eye movement pattern and, for those cycles, evaluate the exact signal tracts in which a subject foveates. About 40 eyemovement recordings, either infrared-oculographic or electrooculographic, were acquired from 16 CN subjects. Results suggest that the use of an adaptive threshold applied to the eye velocity signal could improve the estimation of slow phase start point. This can enhance foveation time computing and reduce influence of repositioning saccades and data noise on the waveform type identification.

Original languageEnglish
Title of host publicationIFMBE Proceedings
Pages1010-1013
Number of pages4
Volume25
Edition4
DOIs
Publication statusPublished - 2009
EventWorld Congress on Medical Physics and Biomedical Engineering: Image Processing, Biosignal Processing, Modelling and Simulation, Biomechanics - Munich, Germany
Duration: Sep 7 2009Sep 12 2009

Other

OtherWorld Congress on Medical Physics and Biomedical Engineering: Image Processing, Biosignal Processing, Modelling and Simulation, Biomechanics
Country/TerritoryGermany
CityMunich
Period9/7/099/12/09

Keywords

  • Congenital nystagmus
  • Eye movement signal processing
  • Foveation
  • Slow phase

ASJC Scopus subject areas

  • Biomedical Engineering
  • Bioengineering

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