PII: S0022-510X(02)00204-6

Abstract

We thank Dr. Gilmore for his interest in our article [ [1] Pieri V. Diederich N.J. Raman R. Goetz C.G. Decreased color discrimination and contrast sensitivity in Parkinson's disease. J. Neurol. Sci. 2000; 172: 7-11 Abstract Full Text Full Text PDF PubMed Scopus (126) Google Scholar ]. He contested the way we calculated the contrast sensitivity scores of the Vis-Tech tests. In fact, we applied the same method as Price et al. [ [2] Price M.J. Feldman R.G. Adelberg D. Kayne H. Abnormalities in color vision and contrast sensitivity in Parkinson's disease. Neurology. 1992; 42: 887-890 Crossref PubMed Google Scholar ], and used the number of the last discernible patch to define contrast sensitivity (CS). Using similar methodology, we were therefore able to show that the numeric results in our study were comparable to those described by Price et al. We agree, however, with Dr, Gilmore that operative definitions of CS vary. In the physiological sense, CS should be correctly defined as the reciprocal of contrast threshold for a particular spatial frequency. Similarly, contrast sensitivity function is determined by log–log plotting of CS for different frequencies [ [3] Hutton J.T. Morris J.L. Elias J.W. Varma R. et al. Spatial contrast sensitivity is reduced in bilateral Parkinson's disease. Neurology. 1991; 41: 1200-1203 Crossref PubMed Google Scholar ]. Consequently and as proposed by Dr. Gilmore, some authors have performed a logarithmic transformation of the data [ [4] Struck L.K. Rodnitzki R.L. Dobson J.K. Circadian fluctuations of contrast sensitivity in Parkinson's disease. Neurology. 1990; 40: 467-470 Crossref PubMed Google Scholar ]. Still others have proposed that altered CS be expressed in terms of decibel (dB) changes related to the normal CS curve or 0 line [ [5] Tagliati M. Brannan J.R. Bodis-Wollner I. Contrast sensitivity in PD. Neurology. 1992; 42: 1126-1127 Crossref PubMed Google Scholar ]. No universally accepted method has been established and even the guidelines for data presentation by the manufacturer [ [6] Vistech Consultants, Inc: Instructions for VCTS∴ 6500, 1988. Google Scholar ] are confusing, with CS on one side of the diagram, contrast threshold on the other, and the numerically defined patches (chosen by us) in-between.