title: Full-field electroretinogram in autism spectrum disorder.
abstract: OBJECTIVE
  To explore early findings that individuals with autism spectrum disorder (ASD) have reduced scotopic ERG b-wave amplitudes.
  
  
  METHODS
  Light-adapted (LA) and dark-adapted (DA) ERGs were produced by a range of flash strengths that included and extended the ISCEV standard from two subject groups: a high-functioning ASD group N = 11 and a Control group N = 15 for DA and N = 14 for LA ERGs who were matched for mean age and range. Flash strengths ranged from DA -4.0 to 2.3 log phot cd s m(-2) and LA -0.5 to 1.0 log phot cd s m(-2), and Naka-Rushton curves were fitted to DA b-wave amplitude over the first growth limb (-4.0 to -1.0 log phot cd s m(-2)). The derived parameters (V max, K m and n) were compared between groups. Scotopic 15-Hz flicker ERGs (14.93 Hz) were recorded to 10 flash strengths presented in ascending order from -3.0 to 0.5 log Td s to assess the slow and fast rod pathways, respectively. LA 30-Hz flicker ERGs, oscillatory potentials (OPs) and the responses to prolonged 120-ms ON-OFF stimuli were also recorded.
  
  
  RESULTS
  The ISCEV LA b-wave amplitude produced by 0.5 log phot cd s m(-2) was lower in the ASD group (p < 0.001). Repeated measures ANOVA for the LA b-wave amplitude series forming the photopic hill was significantly (p = 0.01) different between groups. No group differences were observed for the distributions of the time to peaks of LA a-wave, b-wave or the photopic negative responses (phNR) (p > 0.08) to the single flash stimuli, but there was a significant difference in the distribution for the LA b-wave amplitudes (corrected p = 0.006). The prolonged 120-ms ON responses were smaller in the ASD group (corrected p = 0.003), but the OFF response amplitude (p > 0.6) and ON and OFF times to peaks (p > 0.4) were similar between groups. The LA OPs showed an earlier bifurcation of OP2 in the younger ASD participants; however, no other differences were apparent in the OPs or 30-Hz flicker waveforms. DA b-wave amplitudes fell below the control 5th centile of the controls for some individuals including four ASD participants (36 %) at the 1.5 log phot cd s m(-2) flash strength and two (18%) ASD participants at the lower -2 log phot cd s m(-2) flash strength. However, across the 13 flash strengths, there were no significant group differences for b-wave amplitude's growth (repeated measures ANOVA p = 0.83). Nor were there any significant differences between the groups for the Naka-Rushton parameters (p > 0.09). No group differences were observed in the 15-Hz scotopic flicker phase or amplitude (p > 0.1), DA ERG a-wave amplitude or time to peak (p > 26). The DA b-wave time to peak at 0.5 log phot cd s m(-2) was longer in the ASD group (p = 0.04).
  
  
  CONCLUSIONS
  Under LA conditions, the b-wave is reduced across the ASD group, along with the ON response of the prolonged flash ERG. Some ASD individuals also show subnormal DA ERG b-wave amplitudes. These exploratory findings suggest there is altered cone-ON bipolar signalling in ASD.
authors: Department of Optometry and Vision Science, Flinders University, GPO Box 2100, Adelaide, SA, 5001, Australia. paul.constable@flinders.edu.au.|Autism Research Group, City University London, London, UK. paul.constable@flinders.edu.au.
authors: Paul A
authors: http://orcid.org/0000-0002-3994-1700
authors: PA
authors: Constable
authors: Autism Research Group, City University London, London, UK.
authors: Sebastian B
authors: SB
authors: Gaigg
authors: Autism Research Group, City University London, London, UK.
authors: Dermot M
authors: DM
authors: Bowler
authors: Department of Ophthalmology, University Clinic, Regensburg, Germany.
authors: Herbert
authors: H
authors: Jägle
authors: Clinical and Academic Department of Ophthalmology, Great Ormond Street Hospital for Children, Great Ormond Street, London, UK.
authors: Dorothy A
authors: DA
authors: Thompson
mesh_terms: D000293:Adolescent; D000328:Adult; D000067877:Autism Spectrum Disorder / Q000503:physiopathology*; D002648:Child; D003623:Dark Adaptation / Q000502:physiology; D004596:Electroretinography; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D055254:Night Vision / Q000502:physiology; D010775:Photic Stimulation; D058468:Receptors, Ionotropic Glutamate / Q000502:physiology; D018094:Receptors, Metabotropic Glutamate / Q000502:physiology; D012160:Retina / Q000503:physiopathology*; D051245:Retinal Bipolar Cells / Q000502:physiology; D017949:Retinal Cone Photoreceptor Cells / Q000502:physiology; D055815:Young Adult
chemical_list: D058468:Receptors, Ionotropic Glutamate; D018094:Receptors, Metabotropic Glutamate
keywords: 15-Hz scotopic flicker; Autism spectrum disorder; Electroretinogram; Naka-Rushton; ON pathway