title: Effects of stimulus blocking, light scattering, and distortion on multifocal electroretinogram.
abstract: OBJECTIVE
  To investigate how the multifocal electroretinogram (ERG) is altered in conditions of blocking, light scattering, or distortion of the stimulus that are seen in ocular pathologies.
  
  
  METHODS
  A central 40 degree-diameter stimulus pattern consisting of 61 hexagons was presented on a cathode ray tube monitor at a rate of 75 Hz according to the pseudo-random binary M sequence by the Veris computer program. Localized responses corresponding to each hexagon and ERG topographies were displayed on the computer screen. Central scotoma was simulated by blocking the central area of the stimulus, visual field constriction by blocking the outer area of the stimulus, mild cataract by using acrylic filters that caused light scatter, and epiretinal membrane by using a wavy plastic plate that produced metamorphopsia.
  
  
  RESULTS
  The responses from the blocked area were nonrecordable whether blockage was central or peripheral; responses from the adjacent unblocked area had a larger amplitude when large areas of the stimulus were blocked. The light scatter that decreased vision from 20/20 to 20/70 did not significantly decrease response amplitudes. Responses from areas in which the stimulus pattern was distorted were minimally affected.
  
  
  CONCLUSIONS
  The results show that the system records local ERGs from the macula and outside the macula. It can detect the area where the stimulus is blocked. Moderate light scattering and distortion do not cause loss of local ERG characteristics.
authors.affiliation: Schepens Retina Associates, Schepens Eye Research Institute, Department of Ophthalmology, Harvard Medical School, Boston 02114, MA, USA.
authors.forename: M
authors.initials: M
authors.lastname: Arai
authors.forename: J M
authors.initials: JM
authors.lastname: Lopes de Faria
authors.forename: T
authors.initials: T
authors.lastname: Hirose
mesh_terms: D000328:Adult; D004596:Electroretinography; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008027:Light; D008297:Male; D010775:Photic Stimulation; D012160:Retina / Q000502:physiology*; D012542:Scattering, Radiation; D012607:Scotoma / Q000503:physiopathology; D014792:Visual Acuity; D014794:Visual Fields