title: Foveal cone involvement in retinitis pigmentosa progression assessed through flash-on-flash parameters.
abstract: OBJECTIVE
  To compare psychophysical Naka-Rushton parameters in retinitis pigmentosa (RP) patients and healthy controls using a flash-on-flash increment threshold paradigm, and to measure changes of these parameters with RP progression.
  
  
  METHODS
  Sixty-six RP patients and 10 normal subjects were tested, and their maximum response (Rmax), half-saturation intensity (sigma), and slope (n) parameters were estimated.
  
  
  CONCLUSIONS
  Rmax in RP patients is decreased significantly with respect to the range in normal controls and continues to decrease (0.024 log units/yr) with disease progression. The distribution of sigma in RP patients differs from that in normal subjects, showing lower values in general, but no progression. Small differences in parameter distributions among genetic or pathophysiologic RP subcategorizations were found, but these do not fulfill stricter statistical criteria required for multiple comparisons. Measurement noise, inherent in the flash-on-flash paradigm, exert considerable influence on the quality of the data, as was demonstrated through repeated measures and a Monte Carlo simulation.
authors.affiliation: Wilmer Ophthalmological Institute, Johns Hopkins University School of Medicine, Baltimore, Maryland.
authors.forename: G
authors.initials: G
authors.lastname: Dagnelie
authors.forename: R W
authors.initials: RW
authors.lastname: Massof
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D005584:Fovea Centralis / Q000503:physiopathology*; D006801:Humans; D008027:Light; D008875:Middle Aged; D009010:Monte Carlo Method; D010786:Photoreceptor Cells / Q000503:physiopathology; D011601:Psychophysics; D015203:Reproducibility of Results; D012174:Retinitis Pigmentosa / Q000503:physiopathology*; D012684:Sensory Thresholds; D014796:Visual Perception