title: Cone dystrophy with "supernormal" rod ERG: psychophysical testing shows comparable rod and cone temporal sensitivity losses with no gain in rod function.
abstract: OBJECTIVE
  We report a psychophysical investigation of 5 observers with the retinal disorder "cone dystrophy with supernormal rod ERG," caused by mutations in the gene KCNV2 that encodes a voltage-gated potassium channel found in rod and cone photoreceptors. We compared losses for rod- and for cone-mediated vision to further investigate the disorder and to assess whether the supernormal ERG is associated with any visual benefit.
  
  
  METHODS
  L-cone, S-cone, and rod temporal acuity (critical flicker fusion frequency) were measured as a function of target irradiance; L-cone temporal contrast sensitivity was measured as a function of temporal frequency.
  
  
  RESULTS
  Temporal acuity measures revealed that losses for vision mediated by rods, S-cones, and L-cones are roughly equivalent. Further, the gain in rod function implied by the supernormal ERG provides no apparent benefit to near-threshold rod-mediated visual performance. The L-cone temporal contrast sensitivity function in affected observers was similar in shape to the mean normal function but only after the mean function was compressed by halving the logarithmic sensitivities.
  
  
  CONCLUSIONS
  The name of this disorder is potentially misleading because the comparable losses found across rod and cone vision suggest that the disorder is a generalized cone-rod dystrophy. Temporal acuity and temporal contrast sensitivity measures are broadly consistent with the defect in the voltage-gated potassium channel producing a nonlinear distortion of the photoreceptor response but after otherwise normal transduction processes.
authors.affiliation: UCL Institute of Ophthalmology, University College London, London, United Kingdom.
authors.forename: Andrew
authors.initials: A
authors.lastname: Stockman
authors.forename: G Bruce
authors.initials: GB
authors.lastname: Henning
authors.forename: Michel
authors.initials: M
authors.lastname: Michaelides
authors.forename: Anthony T
authors.initials: AT
authors.lastname: Moore
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Webster
authors.forename: Jocelyn
authors.initials: J
authors.lastname: Cammack
authors.forename: Caterina
authors.initials: C
authors.lastname: Ripamonti
mesh_terms: D000328:Adult; D015350:Contrast Sensitivity / Q000502:physiology; D004596:Electroretinography; D005260:Female; D005425:Flicker Fusion / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D024642:Potassium Channels, Voltage-Gated / Q000235:genetics; D011601:Psychophysics; D017949:Retinal Cone Photoreceptor Cells / Q000502:physiology*; D017948:Retinal Rod Photoreceptor Cells / Q000502:physiology*; D012174:Retinitis Pigmentosa / Q000235:genetics / Q000503:physiopathology*; D012680:Sensitivity and Specificity; D014792:Visual Acuity / Q000502:physiology
chemical_list: C489610:KCNV2 protein, human; D024642:Potassium Channels, Voltage-Gated
keywords: KCNV2 gene; cone dystrophy; cone-rod dystrophies; critical flicker fusion; flicker sensitivity; supernormal rod ERG; temporal acuity; temporal processing