May 1992
Volume 33, Issue 6
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Articles  |   May 1992
Contrast thresholds for letter identification in retinitis pigmentosa.
Author Affiliations
  • K R Alexander
    Department of Ophthalmology and Visual Sciences, Chicago College of Medicine, University of Illinois 60612.
  • D J Derlacki
    Department of Ophthalmology and Visual Sciences, Chicago College of Medicine, University of Illinois 60612.
  • G A Fishman
    Department of Ophthalmology and Visual Sciences, Chicago College of Medicine, University of Illinois 60612.
Investigative Ophthalmology & Visual Science May 1992, Vol.33, 1846-1852. doi:
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      K R Alexander, D J Derlacki, G A Fishman; Contrast thresholds for letter identification in retinitis pigmentosa.. Invest. Ophthalmol. Vis. Sci. 1992;33(6):1846-1852.

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

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Abstract

To assess mechanisms of foveal vision loss in retinitis pigmentosa (RP), contrast thresholds were measured for the identification of Sloan letters at four adapting field luminances (0.4, 1.4, 2.4, and 3.4 log td) in a group of 16 patients with RP who had best-corrected Snellen visual acuities of 20/30 or better, minimal or no posterior subcapsular cataracts, and no atrophic or cystic-appearing foveal lesions. Letter contrast sensitivities of the patients with RP were reduced below those of a group of ten subjects with normal vision for all letter sizes and at all adapting field luminances. The overall pattern of these results indicated that neither a reduced quantal absorption by foveal cones nor spatial undersampling from a loss of foveal cones accounted for the reductions in letter contrast sensitivities. The findings were most consistent with a uniform increase in intercone spacing in the foveas of this group of patients with RP and mild visual acuity loss.

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