title: Retinal sensitivity to flicker modulation: reduced by early age-related maculopathy.
abstract: OBJECTIVE
  To evaluate retinal, cone-mediated flicker sensitivity (CFS) in age-related maculopathy (ARM) by quantifying response gain and threshold of the focal electroretinogram (FERG) to flicker modulation.
  
  
  METHODS
  Nineteen patients with ARM (visual acuity > or =20/30) and 11 age-matched control subjects were examined. Twelve patients had less than 20 soft drusen in the macular region and no hyper-/hypopigmentation (early lesion), whereas seven had more than 20 soft drusen and/or focal hyper-/hypopigmentation (advanced lesion). Macular (18 degree ) FERGs were elicited by a sinusoidally flickering (41 Hz) uniform field (on a light-adapting background) whose modulation depth was varied between 16.5% and 94%. Amplitude and phase of the response's fundamental harmonic were measured.
  
  
  RESULTS
  In both control subjects and patients with ARM, log FERG amplitude increased with log stimulus modulation depth with a straight line (power law) relation. However, the slope (or gain) of the function was, on average, steeper in control subjects than in patients with either early or advanced lesions. Mean FERG threshold, estimated from the value of the log modulation depth that yielded a criterion response, did not differ between control subjects and patients with early lesions but was increased (0.35 log units) compared with control subjects in those with advanced lesions. In both patient groups, but not in control subjects, mean FERG phase tended to delay with decreasing stimulus modulation depth.
  
  
  CONCLUSIONS
  Retinal CFS losses can be detected in ARM by evaluating the FERG as a function of flicker modulation depth. Reduced response gain and phase delays, with normal thresholds, are associated with early lesions. Increased response thresholds, in addition to gain and phase abnormalities, may reflect more advanced lesions. Evaluating CFS by FERG may directly document different stages of macular dysfunction in ARM.
authors.affiliation: Istituto di Oftalmologia, Università Cattolica del S. Cuore, Rome, Italy. md0571@mclink.it
authors.forename: B
authors.initials: B
authors.lastname: Falsini
authors.forename: A
authors.initials: A
authors.lastname: Fadda
authors.forename: G
authors.initials: G
authors.lastname: Iarossi
authors.forename: M
authors.initials: M
authors.lastname: Piccardi
authors.forename: D
authors.initials: D
authors.lastname: Canu
authors.forename: A
authors.initials: A
authors.lastname: Minnella
authors.forename: S
authors.initials: S
authors.lastname: Serrao
authors.forename: L
authors.initials: L
authors.lastname: Scullica
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D003117:Color Vision Defects / Q000503:physiopathology*; D004596:Electroretinography / Q000379:methods; D005260:Female; D005425:Flicker Fusion; D006801:Humans; D008268:Macular Degeneration / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D017949:Retinal Cone Photoreceptor Cells / Q000503:physiopathology*; D014792:Visual Acuity