title: Effect of optical defocus on multifocal ERG responses.
abstract: BACKGROUND
  Multifocal electroretinography (mfERG) is a sensitive technique to probe retinal function topographically. Various conditions such as macular degeneration decrease the first-order kernel (K1) response magnitude of mfERG. Previous studies have given inconsistent results on the effect of optical defocus due to poor controls. This study investigated the effect of optical defocus on the K1 response of the central retina using a well-controlled method.
  
  
  METHODS
  Twenty subjects were recruited to undergo mfERG measurement using the VERIS 4.0 system. A four millimetre artificial pupil was fitted before each fully-dilated right eye, optically corrected for the viewing distance. The implicit times and response amplitudes of n1 (first negative trough) and p1 (first positive peak) under three different optical defocus conditions (zero dioptres, +1.00 D and +3.00 D) were measured.
  
  
  RESULTS
  The implicit times of n1 and p1 did not demonstrate any significant variation from the central macula to para-macula under different optical defocus conditions. The response amplitude of n1 did not show any changes from the central macula to para-macula but the response amplitude of the central macular p1 showed a significant reduction by 12 per cent under +1.00 D defocus and +3.00 D defocus.
  
  
  CONCLUSIONS
  Optical defocus causes mild reduction in mfERG at the central macula but there are no significant changes in the periphery. A full optical correction is recommended for mfERG measurement to minimise the reduction of the macular response due to optical defocus.
authors.affiliation: Department of Optometry and Radiography, The Hong Kong Polytechnic University, Kowloon, Hong Kong SAR, China.
authors.forename: Ho-Lung
authors.initials: HL
authors.lastname: Chan
authors.forename: Andrew W
authors.initials: AW
authors.lastname: Siu
mesh_terms: D000065:Accommodation, Ocular / Q000502:physiology*; D000328:Adult; D004596:Electroretinography / Q000379:methods; D006801:Humans; D008266:Macula Lutea / Q000502:physiology; D011930:Reaction Time; D012160:Retina / Q000502:physiology*