December 1987
Volume 28, Issue 12
Free
Articles  |   December 1987
Diurnal rhythm in the human rod ERG: retinitis pigmentosa.
Author Affiliations
  • D G Birch
    Retina Foundation of the Southwest, Presbyterian Medical Center, Dallas, Texas 75231.
Investigative Ophthalmology & Visual Science December 1987, Vol.28, 2042-2048. doi:
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      D G Birch; Diurnal rhythm in the human rod ERG: retinitis pigmentosa.. Invest. Ophthalmol. Vis. Sci. 1987;28(12):2042-2048.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Rod ERGs were measured at three times of day over an extensive range of retinal illuminances in six light-entrained patients with autosomal recessive or isolate forms of retinitis pigmentosa and at five times of day in six light-entrained normal volunteers. B-wave amplitude versus retinal illuminance functions from each time of day were described by determining the parameters of the best-fit Naka-Rushton function. Results from normal subjects showed that rod ERG threshold (defined as the log retinal illuminance necessary to elicit a 2.0 microV response) was elevated 1 1/2 hr after daily light-onset due to both an increase in log k (semi-saturation constant) and a decrease in log Vmax (maximum rod amplitude). The magnitude of the threshold elevation 1 1/2 hr after light-onset was comparable in patients with retinitis pigmentosa and normal subjects. Whereas thresholds returned to pre-light exposure levels rapidly during the light-phase of the daily cycle in normal subjects, thresholds continued to rise in patients with retinitis pigmentosa due primarily to a further increase in log k. These findings are consistent with abnormal rod photoreceptor disc renewal mechanisms in retinitis pigmentosa.

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