title: Quantifying the ON and OFF Contributions to the Flash ERG with the Discrete Wavelet Transform.
abstract: OBJECTIVE
  Discrete wavelet transform (DWT) analyses suggest that the 20- and 40-Hz components of the short-flash photopic electroretinogram (ERG) are closely related to the ON and OFF pathways, respectively. With the DWT, we examined how the ERG ON and OFF components are modulated by the stimulus intensity and/or duration.
  
  
  METHODS
  Discrete wavelet transform descriptors (20, 40 Hz and 40:20-Hz ratio) were extracted from ERGs evoked to 25 combinations of flash durations (150-5 ms) and strengths (0.8-2.8 log cd.m-2).
  
  
  RESULTS
  In ERGs evoked to the 150-ms stimulus (to separate the ON and OFF ERGs), the 40:20-Hz ratio of ON ERGs (mean ± SD: 0.49 ± 0.04) was significantly smaller (P< 0.05) than that of OFF ERGs (1.71 ± 0.18) owing to a significantly (P< 0.05) higher contribution of the 20 and 40 Hz components to the ON and OFF ERGs, respectively. With brighter stimuli, the ON and OFF components increased similarly (P < 0.05). While progressively shorter flashes had no impact (P> 0.05) on the ON component, it exponentially enhanced (P< 0.05) the OFF component.
  
  
  CONCLUSIONS
  Discrete wavelet transform allows for an accurate determination of ON and OFF retinal pathways even in ERGs evoked to a short flash. To our knowledge, the significant OFF facilitatory effect evidenced with shorter stimuli has not previously been reported.
  
  
  CONCLUSIONS
  The DWT approach should offer a rapid, easy, and reproducible approach to retrospectively and prospectively evaluate the function of the retinal ON and OFF pathways using the standard (short-flash duration) clinical ERG stimulus.
authors.affiliation: Department of Ophthalmology & Neurology-Neurosurgery, Research Institute of the McGill University Health Centre/Montreal Children's Hospital, Montreal, Quebec, Canada.
authors.forename: Mathieu
authors.initials: M
authors.lastname: Gauvin
authors.affiliation: Eye Hospital, University Medical Centre, Ljubljana, Slovenia.
authors.forename: Maja
authors.initials: M
authors.lastname: Sustar
authors.affiliation: Department of Ophthalmology & Neurology-Neurosurgery, Research Institute of the McGill University Health Centre/Montreal Children's Hospital, Montreal, Quebec, Canada.
authors.forename: John M
authors.initials: JM
authors.lastname: Little
authors.affiliation: Eye Hospital, University Medical Centre, Ljubljana, Slovenia.
authors.forename: Jelka
authors.initials: J
authors.lastname: Brecelj
authors.affiliation: Département de Génie Électrique, École de Technologie Supérieure, Montréal, Québec, Canada ; Centre de Recherches Mathématiques, Montréal, Québec, Canada.
authors.forename: Jean-Marc
authors.initials: JM
authors.lastname: Lina
authors.affiliation: Department of Ophthalmology & Neurology-Neurosurgery, Research Institute of the McGill University Health Centre/Montreal Children's Hospital, Montreal, Quebec, Canada.
authors.forename: Pierre
authors.initials: P
authors.lastname: Lachapelle
keywords: ON and OFF; electroretinogram; human; stimulus duration; stimulus strength; wavelet transform