Quantitative electroretinogram measures of phototransduction in cone and rod photoreceptors: normal aging, progression with disease, and test-retest variability

Arch Ophthalmol. 2002 Aug;120(8):1045-51. doi: 10.1001/archopht.120.8.1045.


Objectives: To determine (1) reference values for cone and rod phototransduction variables derived from the a-wave of the electroretinogram, (2) their dependence on age, (3) the progression in cone and rod variables in patients with X-linked retinitis pigmentosa (XLRP), and (4) the test-retest variability in these a-wave measures compared with the variability in cone and rod b-wave measures.

Participants: One hundred control subjects aged 5 to 75 years and 24 patients with XLRP aged 5 to 38 years.

Methods: High-intensity stimuli were used to elicit electroretinograms in the dark and in the presence of a rod-saturating background. Computer averaging and computer subtraction of cone components from mixed rod-cone responses were used to derive rod-only and cone a-waves. Rod and cone phototransduction variables were derived by computer fitting physiologically based computational models to the leading edges of a-wave ensembles.

Results: Phototransduction efficiency, as indexed by the sensitivity variable (S), decreased with age for cone and rod-only responses, whereas maximum cone and rod photoresponses (Rm(P3)) remained constant. In patients with XLRP tested annually for 4 years, Rm(P3) for rods and, to a lesser extent, cones declined with disease progression, whereas S remained stable. The test-retest variability in the a-wave Rm(P3) is lower than previously reported measures of the variability in b-wave peak-to-peak amplitude.

Conclusion: The leading edge of the a-wave of the electroretinogram can be related to rod and cone phototransduction variables through quantitative models. Rm(P3), rather than S, should be the outcome measure of choice when using the a-wave to follow photoreceptor function in prospective studies and treatment trials.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Aging / physiology*
  • Child
  • Child, Preschool
  • Dark Adaptation
  • Disease Progression
  • Electroretinography*
  • Female
  • Genetic Linkage
  • Humans
  • Male
  • Middle Aged
  • Photoreceptor Cells, Vertebrate / physiology*
  • Reference Values
  • Reproducibility of Results
  • Retinitis Pigmentosa / genetics
  • Retinitis Pigmentosa / physiopathology*
  • Vision, Ocular / physiology*
  • X Chromosome