title: Effect of axial length on full-field and multifocal electroretinograms.
abstract: OBJECTIVE
  The aim was to investigate the effect of axial length on full-field electroretinogram (ffERG) and multifocal electroretinogram (mfERG) in young Indian subjects.
  
  
  METHODS
  One hundred subjects (44 male) with refractive errors from +0.50 to -18.00 DS and no myopic retinopathy underwent axial length measurement. ffERG was measured, which included scotopic and photopic responses according to International Society for Clinical Electrophysiology of Vision (ISCEV) guidelines. The mfERG was recorded after correcting for refractive error according to ISCEV standards. The dark-adapted and light-adapted parameters of ffERG and N1, P1 parameters of six rings in mfERG were analysed with axial length, controlled for refractive error. The subjects were divided into seven groups based on axial length. The b/a ratio of dark-adapted and light-adapted 3.0 ffERG and P1/N1 ratio of mfERG amplitudes were analysed for seven groups of axial length.
  
  
  RESULTS
  The axial length ranged from 21.79 to 30.55 mm. Significant negative correlations were noted for ffERG and mfERG amplitudes, whereas implicit times showed minimal delay with increase in axial length. In ffERG, the scotopic responses were more decreased compared to photopic responses. In mfERG, P1 and N1 amplitudes were significantly decreased in all the rings in all groups and more reduction was noted in the central ring compared to peripheral rings. The P1 amplitudes were more affected as compared to N1 amplitudes. The light-adapted and dark-adapted 3.0 ERG b/a ratio and P1/N1 ratio for seven axial length groups did not show statistically significant difference. The ERG parameters were not significant with refractive error.
  
  
  CONCLUSIONS
  This study quantifies the relationship of axial length with ffERG and mfERG parameters in a young Indian population. Although the amplitudes were reduced significantly, the implicit times were not significantly affected. The ERG parameters were more related to axial length than refractive error. Hence, interpretation of ffERG and mfERG parameters needs careful consideration in subjects with increasing axial length.
authors.affiliation: Department of Optometry, Medical Research Foundation, Chennai, Tamil Nadu, India.|Elite School of Optometry, Unit of Medical Research Foundation, Chennai, Tamil Nadu, India.
authors.forename: Ramya
authors.initials: R
authors.lastname: Sachidanandam
authors.affiliation: Department of Optometry, Medical Research Foundation, Chennai, Tamil Nadu, India.|Elite School of Optometry, Unit of Medical Research Foundation, Chennai, Tamil Nadu, India.
authors.forename: Priya
authors.initials: P
authors.lastname: Ravi
authors.affiliation: Department of Vitreoretina, Medical Research Foundation, Chennai, Tamil Nadu, India.
authors.forename: Parveen
authors.initials: P
authors.lastname: Sen
mesh_terms: D000328:Adult; D058452:Axial Length, Eye / Q000033:anatomy & histology / Q000502:physiology*; D055253:Color Vision / Q000502:physiology; D003623:Dark Adaptation / Q000502:physiology; D004596:Electroretinography; D005260:Female; D006801:Humans; D008297:Male; D055254:Night Vision / Q000502:physiology; D012030:Refractive Errors / Q000503:physiopathology; D012160:Retina / Q000502:physiology*; D014794:Visual Fields / Q000502:physiology*; D055815:Young Adult
keywords: axial length; full-field electroretinogram; multifocal electroretinogram; myopia