title: Rod sensitivity, cone sensitivity, and photoreceptor layer thickness in retinal degenerative diseases.
abstract: OBJECTIVE
  To evaluate the effects of selective rod and/or cone loss on frequency-domain optical coherence tomography (fdOCT) measures of photoreceptor structure in patients with retinal degenerative diseases.
  
  
  METHODS
  Six patients with cone dystrophy (CD) and eight patients with retinitis pigmentosa (RP) were recruited from the Southwest Eye Registry on the basis of diagnosis and ERG findings. fdOCT horizontal line scans were segmented to obtain the thicknesses of the outer segments plus RPE (OS+) and the outer nuclear layer (ONL). The normalized product ONL*OS was obtained after dividing by mean ONL*OS values of 23 normal individuals. Visual field sensitivity profiles were obtained with a modified retinal perimeter, from the horizontal midline with short- and long-wave stimuli under dark- and light-adapted conditions.
  
  
  RESULTS
  Patients with CD and normal rod-mediated sensitivity, but decreased cone-mediated sensitivity, showed normal ONL*OS outside the fovea. The total receptor layer was thinned in the fovea, consistent with loss in cone nuclei and Henle's fiber layer. Patients with RP and sensitivity in the dark that was mediated by cones showed ONL*OS thickness that was linearly related to cone sensitivity. ONL*OS thickness was linearly related to rod sensitivity in regions with greater loss of cone than rod sensitivity.
  
  
  CONCLUSIONS
  Both rods and cones can support an intact IS/OS junction and normal photoreceptor thickness measures. The product of ONL and OS thicknesses is proportional to the sensitivity mediated by the less abnormal type of photoreceptor.
authors.affiliation: Retina Foundation of Southwest, 9900 N. Central Expressway, Suite 400, Dallas, TX 75231, USA. dbirch@retinafoundation.org
authors.forename: David G
authors.initials: DG
authors.lastname: Birch
authors.forename: Yuquan
authors.initials: Y
authors.lastname: Wen
authors.forename: Kelly
authors.initials: K
authors.lastname: Locke
authors.forename: Donald C
authors.initials: DC
authors.lastname: Hood
mesh_terms: D000328:Adult; D000368:Aged; D002648:Child; D003623:Dark Adaptation; D004596:Electroretinography; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D017949:Retinal Cone Photoreceptor Cells / Q000473:pathology*; D012162:Retinal Degeneration / Q000503:physiopathology*; D017948:Retinal Rod Photoreceptor Cells / Q000473:pathology*; D012174:Retinitis Pigmentosa / Q000503:physiopathology; D041623:Tomography, Optical Coherence; D014792:Visual Acuity / Q000502:physiology; D058609:Visual Field Tests; D014794:Visual Fields / Q000502:physiology*